Advances in understanding of pathogenesis of aHUS and HELLP

Advances in understanding of pathogenesis of aHUS and HELLP

Celia J. Fang,1 Anna Richards,2 M. Kathryn Liszewski,1 David Kavanagh3 and John P. Atkinson1

1Department of Medicine, Division of Rheumatology, Washington University School of Medicine, St Louis, MO, USA, 2Department of

Renal Medicine, Royal Infirmary, Little France, Edinburgh, UK, and 3The Institute of Human Genetics, Newcastle University, Newcastle

upon Tyne, UK

Summary

Both atypical haemolytic uraemic syndrome (aHUS) and

the HELLP syndrome (haemolytic anaemia, elevated liver

enzymes, and low platelets) are thrombotic microangiopathies

characterized by microvascular endothelial activation, cell

injury and thrombosis. aHUS is a disease of complement

dysregulation, specifically a gain of function of the alternative

pathway, due to mutations in complement regulatory proteins

and activating components. Recently, the same complement

mutation identified in multiple patients with aHUS was found

in a patient with the HELLP syndrome. The pathogeneses of

both diseases are reviewed focusing on the role of the

complement system and how its dysfunction could result in

a thrombotic microangiopathy in the kidney in the case of

aHUS and in the liver in the case of the HELLP syndrome.

Keywords: thrombotic microangiopathy (TMA), aHUS, pre-

eclampsia, HELLP, alternative pathway of complement.

The thrombotic microangiopathy (TMA) disorders represent

clinically diverse entities featuring a disruption of the micro-

vascular endothelium. Atypical haemolytic uraemic syndrome

(aHUS) and HELLP (haemolytic anaemia, elevated liver

enzymes, and low platelets) syndrome belong to this group.

They are characterized by microvascular endothelial injury

events that lead to microthrombi. Fragmented red blood cells

result from the abnormally high levels of shear stress produced

as blood flows through turbulent areas of the microcirculation

(e.g. kidneys and liver) that are partially occluded by platelet

and fibrin thrombi. Thrombocytopenia occurs secondary to

platelet activation and accelerated consumption. Elevated

serum enzymes, e.g. alanine transaminase, are derived from

ischemic or necrotic tissue and from the lysed red cells.

Disorders that are listed under the umbrella of TMA share

clinical and serological characteristics. Correct diagnosis may

be difficult but desirable as distinct therapeutic strategies may

be mandated. For example, the clinical syndrome of HUS

commonly comprises part of the diagnostic pentad of throm-

botic thrombocytopenic purpura (TTP): thrombocytopenia,

microangiopathic haemolytic anaemia (MAHA), renal dys-

function, neurological symptoms and signs, and fever. Overlap

occurs as renal abnormalities are encountered in TTP patients

and extra-renal manifestations may be present in patients with

HUS. However, HUS is often considered to be primarily a renal

disease with limited systemic complications while TTP is a

systemic disease with a relatively low frequency of renal disease.

Thrombotic thrombocytopenic purpura is now understood

to result in most cases from a hereditary (including congenital)

or acquired severe deficiency of the metalloprotease enzyme,

ADAMTS13 (a disintegrin and metalloproteinase with a

thrombospondin type 1 motif, member 13) (Veyradier et al,

2003; Tsai, 2006). This protease cleaves the high molecular

weight von Willebrand factor (VWF) oligomers secreted by

endothelial cells, resulting in unusually large multimers of

circulating VWF. They can aggregate to form microvascular

platelet thrombi at intravascular sites with high shear stress.

Plasma exchange therapy reduces the mortality from 85–100%

to 10–30% (Rock et al, 1991). There are two main subtypes of

HUS: diarrhoeal-associated/epidemic (D+ HUS) or non-

diarrhoeal/atypical HUS (D) or aHUS). D+ HUS accounts

for a majority of cases and is commonly caused by a preceding

illness with verocytotoxin-producing bacteria, usually Escher-

ichia coli O157:H7. The vero- or shiga-toxin mediates the

damage to glomerular endothelial cells of the kidney (Tarr

et al, 2005). aHUS is rare, may be familial, and has a poorer

prognosis with death rates up to 25% in the acute phase and

50% of patients require ongoing renal replacement (Richards

et al, 2007a). A defect in the regulation of the complement

cascade accounts for about half of cases of aHUS and will be

discussed further in this review.

The HELLP syndrome is not the only TMA that complicates

pregnancy. Pregnancy may also be a precipitant for aHUS

(Noris & Remuzzi, 2005) and TTP (Zheng & Sadler, 2008).

Temporal association may help to identify which disease

process is occurring. HELLP occurs in the third trimester in

70% of patients, although cases in the second trimester and

postpartum period, usually in the first 1–2 d, are well

recognized (Mihu et al, 2007). TTP mostly presents in the

Correspondence: John P. Atkinson, Division of Rheumatology,

Washington University School of Medicine, 660 South Euclid Avenue,

Campus Box 8045, St Louis, MO 63110, USA.

E-mail: [email protected]

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First published online 4 August 2008 ª 2008 The Authorsdoi:10.1111/j.1365-2141.2008.07324.x Journal Compilation ª 2008 Blackwell Publishing Ltd, British Journal of Haematology, 143, 336–348

third trimester or postpartum (George, 2003). aHUS is rare

and almost all cases have been described in the postpartum

period (within 48 h up to 10 weeks) (Sibai, 2007). Recently,

the same complement mutation was found in patients with

aHUS and in a patient with the HELLP syndrome (Fang et al,

2008). However, we are aware of several series of patients with

severe pre-eclampsia or HELLP syndrome in which approx-

imately one-third of patients appear to have mutations in

complement regulatory proteins (J. Salmon, V. Fremeaux-

Bacchi and J.P. Atkinson, unpublished observations). This

review focuses on our current understanding of the pathogen-

esis, especially with respect to the complement system, of

aHUS and the HELLP syndrome.

aHUS

Haemolytic uraemic syndrome is a triad of a MAHA,

thrombocytopenia and renal impairment and is characterized

by endothelial cell injury and activation in the microvascula-

ture of the kidney. The major advance in the past decade has

been the realization that the host’s innate immune response to

the damaged tissue is a key player in disease development

(Kavanagh et al, 2007). The reported annual incidence of

aHUS is approximately two cases/1 000 000 total population

while the incidence of D+ HUS is approximately 10 times that

of aHUS (Constantinescu et al, 2004).

Complement dysregulation causes defectiveprotection of endothelial cells

Recent advances have shown that aHUS is a disease of

excessive complement activation on host tissue, particularly

along the renal glomerular and arteriolar endothelial and

basement membranes. An injury or trigger leads to the loss of

endothelial cell integrity, the activation of pro-coagulation

pathways and development of the TMA (Fig 1A and B). Over

(A)

(B)

Fig 1. Effects of the alternative pathway on endothelial cells. (A) Initially, C3b is deposited on injured or stressed endothelial cells secondary to

natural Ab (classical pathway), lectin (lectin pathway) or spontaneous tickover (alternative pathway or AP) due to recognition of altered self. C3b

formed as shown is inactivated under normal circumstances to prevent excessive amplification through the AP. Factor D (FD), factor B (FB) and

properdin (P) are components of the AP and feedback or amplification loop. However, in the setting of a deficiency in a plasma or membrane

regulator of C3b, undesirable amounts of C3b may be engineered to the further detriment of the cell. Also, if the AP is inadequately regulated,

concomitant with the products of C3b is the release of anaphylatoxin C3a and more cleavage of C5. C5a is also an anaphylatoxin and potent

chemotactic factor while C5b leads to the membrane attack complex (MAC; C5b-9). (B) The sequelae of this poorly controlled AP activation is

thrombus formation at the site of injury that is promoted by (1) opsonins that promotes phagocytosis and thus attracts inflammatory cells, (2)

anaphylatoxins that also promote inflammatory cell recruitment as well as produce cytokines and upregulate procoagulants and adhesins through

C3aR and C5aR signalling, and (3) both lytic destruction by MAC and nonlytic membrane perturbation may lead to thrombosis.

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ª 2008 The AuthorsJournal Compilation ª 2008 Blackwell Publishing Ltd, British Journal of Haematology, 143, 336–348 337

50% of reported cases involve mutations in complement genes

that control the regulation or activation of the alternative

complement pathway (AP) (Table I). Excessive complement

activation may be due to either a failure to adequately prevent

complement activation on host tissue, due to mutations in the

complement regulatory genes, Complement Factor H (CFH),

Membrane Cofactor Protein (CD46, previously known as MCP)

and Complement Factor I (CFI), that control the amplification

or feedback loop of the AP (Fig 1A) or excessive complement

activation on glomerular endothelium due to gain of function

mutations in complement activating genes, Complement Factor

B (CFB) and Complement Component 3 (C3). Furthermore,

single nucleotide polymorphisms involving CFH, CD46, and

C4 binding protein (C4BPA/B), deletion haplotypes of Com-

plement Factor H related proteins 1 (CFHR1) and 3 (CFHR3)

and autoantibodies to factor H (FH) are now recognised to

play a role in the pathogenesis of aHUS. Consideration of the

mechanisms by which each of these mutations predisposes to

the development of TMA has been informative. Schematic

diagrams of each of the regulatory proteins and the site of the

mutations have been noted in three recent reviews (Richards

et al, 2007b; Kavanagh et al, 2008a; Zheng & Sadler, 2008) and

are available at the FH aHUS Mutation Database� website

(http://www.fh-hus.org).

Table I. Mutant proteins in aHUS.

Complement

protein Location

Plasma

concentration

Size

(kDa) Function

Mutation

frequency

in aHUS (%)

% of patients

with reduced

protein level�

Factor H (FH) Plasma 200–600 lg/ml 150 Major regulator

of AP in plasma; CA and DAA

15–30 25

Membrane cofactor

protein (MCP)

Cell surface * 65 Major regulator of

AP on cells; CA

10–13 75

Factor I (FI) Plasma 20–50 lg/ml 88 Serine protease whose

catalytic domain cleaves C3

5–12 40

Factor B (FB) Plasma 100–300 lg/ml 100 Zymogen that carries catalytic

unit of the AP convertases

c. 5� N/A

C3 Plasma 1–1Æ5 mg/ml 190 Central component of the

complement cascade

c. 10� N/A

aHUS, atypical haemolytic uraemic syndrome; AP, alternative pathway; CA, cofactor activity; DAA, decay accelerating activity; N/A, not available.

*Membrane protein.

�Numbers of patients screened are insufficient to be more accurate.

�If a component is low, this becomes the top candidate protein for a mutation, but normal levels do not rule out a mutation.

(A)

(B)

Fig 2. Regulation of the alternative pathway by cofactor activity and decay accelerating activity. The alternative complement pathway is controlled by

regulatory proteins such as factor H (FH) and membrane cofactor protein (MCP; CD46). (A) Both FH and MCP are cofactors for serine protease

factor I (FI) that cleaves C3b to its inactivated form iC3b. (B) FH decays the C3 convertase C3bBb by dissociating the Bb catalytic domain from C3b

that can reform a convertase if not inactivated by cofactor activity. These processes keep the alternative pathway in check.

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ª 2008 The Authors338 Journal Compilation ª 2008 Blackwell Publishing Ltd, British Journal of Haematology, 143, 336–348

Defective regulation of the complement system

Factor H, factor H autoantibodies and factor H-related

proteins. Factor H is an abundant 150-kDa plasma

glycoprotein predominantly synthesized by the liver, but also

by endothelial cells, platelets and fibroblasts (Vik et al, 1990).

FH is the most important fluid-phase regulator of the AP. FH

has cofactor activity (Fig 2A), decay accelerating activity

(Fig 2B) and competes with factor B (FB) for C3b binding

(Richards et al, 2007b). The amino-terminal four repeats of

FH possess the major C3b binding site and the complement

regulatory functions (Alexander & Quigg, 2007; Hocking et al,

2008). FH can also down-regulate complement activation on

host cells and exposed basement membranes in the setting of

trauma, apoptosis or necrosis by binding to

glycosaminoglycans (GAGs) through the carboxyl-terminal

end of FH (Jokiranta et al, 2005).

Complement Factor H mutations were initially shown to

predispose to aHUS by Warwicker et al (1998). Since this

initial description, mutations in CFH have been described in

many large cohorts of aHUS patients and account for between

15% and 30% of cases (Caprioli et al, 2001; Perez-Caballero

et al, 2001; Richards et al, 2001; Neumann et al, 2003; Dragon-

Durey et al, 2004; Venables et al, 2006) (Table I). The vast

majority of CFH mutations are heterozygous and cause either

premature stop codons or single amino acid changes. Incom-

plete penetrance of the reported mutations has been described

in all series, suggesting that the mutants are predisposing

factors for aHUS, requiring an endothelial cell insult to

become manifest (Kavanagh et al, 2008a). Approximately 60%

of the independent mutational events cluster in carboxyl-

terminal region of FH, Complement Control Proteins (CCPs)

19–20, and another 20% are in CCPs 15–18. Other patients

have mutations throughout the gene that often lead to FH

haploinsufficiency, as evidenced by them having c. 50% of the

normal level in plasma.

Functional studies of FH mutants associated with aHUS

have defined defects in binding of mutant FH to GAGs (usually

using heparin), C3b, and endothelial cells (Sanchez-Corral

et al, 2002, 2004; Manuelin et al, 2003; Jokiranta et al, 2005;

Heinen et al, 2006; Jozsi et al, 2006; Vaziri-Sani et al, 2006).

This suggests that mutations in CCPs 19 and 20 interfere with

ligand binding to host cell surfaces and basement membranes.

This reduces the efficiency of control of the AP amplification at

these sites while fluid phase regulation remains relatively

unimpaired.

Nuclear magnetic resonance (NMR) and crystal structures

of CCPs 19 and 20 have recently been published (Herbert et al,

2006; Jokiranta et al, 2006). Structure-based interpretation of

the aHUS-associated mutations demonstrated the likely dis-

ruption of a polyanion binding site in the NMR structure

(Herbert et al, 2006). However, analysis of the crystal structure

suggested that it is binding affinity for C3d and C3b which is

the critical activity perturbed by aHUS-linked mutations

(Jokiranta et al, 2006). These data can perhaps be reconciled

by proposing multiple binding sites within FH interacting with

clusters of C3b and polyanions as being key to its regulatory

activity on membranes.

A transgenic mouse model lacking the terminal five CCP

domains of FH has been developed (Pickering et al, 2007). The

mutant FH produced in these mice failed to bind to

endothelial cells in a manner analogous to the mutations seen

in aHUS individuals. This mouse regulated C3 activation in

plasma normally but spontaneously developed aHUS (Kava-

nagh et al, 2008a). This is an informative mouse model but

does not mimic the typical haploinsufficiency situation in

human aHUS.

Thus, information derived from functional studies, NMR

and crystal structures, and the mouse model suggest that

mutations in CFH observed in aHUS interfere with FH’s

binding to host cell surfaces/basement membranes. In addition

to mutations in CFH, single nucleotide polymorphisms (SNPs)

in CFH have also been associated with aHUS (Caprioli et al,

2003; Esparza-Gordillo et al, 2005; Fremeaux-Bacchi et al,

2005).

Factor H autoantibodies that modulate regulatory activity

are a mechanism for the development of aHUS in 6–11% of

cases (Dragon-Durey et al, 2005; Jozsi et al, 2007, 2008). These

autoantibodies bind to the carboxyl-terminus of FH, inhibit

FH interacting with C3b and possibly heparin binding sites

and thereby decrease regulatory activity (Jozsi et al, 2007).

Subsequently (see next paragraph), a group of patients

producing FH autoantibodies were shown to carry deletions

in the CFH cluster (Jozsi et al, 2008).

In addition to the CFH mutations and polymorphisms, a

haplotype containing a deletion of two of the FH related genes,

CFHR1 and CFHR3, increases the risk of aHUS (Zipfel et al,

2007). Although these proteins bind C3b and heparin, neither

factor H related protein 1 (FHR1) nor factor H related protein

3 (FHR3) has intrinsic cofactor or decay accelerating activity;

however, FHR3 does possess a cofactor-enhancing activity

(Hellwage et al, 1999). Serum from aHUS patients lacking

FHR1 and FHR3 showed an impaired ability to protect

erythrocytes from complement activation (Zipfel et al, 2007).

However, it is as yet unclear whether it is the absence of FHR1

and FHR3 that is responsible for the increased risk of aHUS

per se, or whether this deletion is in linkage disequilibrium

with other susceptibility alleles in CFH. Recently, Jozsi et al

(2008), showed the generation of FH autoantibodies correlates

with deficiency of FHR1 and FHR3. The mechanism by which

a deficiency of FHR1 and FHR3 leads to the generation of FH

autoantibodies is unknown.

Membrane cofactor protein (MCP). Membrane cofactor protein

is a widely expressed C3b/C4b-binding membrane glycoprotein

that serves as an inhibitor of complement activation on host cells

(Liszewski et al, 2005). MCP is expressed by almost every cell

examined with the notable exception of erythrocytes.

Additionally, it is highly expressed in the kidney, particularly

by the endothelium (Kavanagh et al, 2008a). MCP is an

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‘intrinsic’ regulator of the host cell on which it is attached in that

it is a cofactor for the serine protease factor I (FI) to degrade C3b

and C4b deposited on the cell surface on which MCP is expressed

(Fig 2A). Similar to CFH, it is a member of the regulators of

complement activation (RCA) family/gene cluster at 1q32

(Liszewski et al, 2005).

Utilizing the candidate gene approach, a genomic region

containing the RCA cluster on 1q32, was implicated in the

pathogenesis of aHUS (Warwicker et al, 1998). Subsequently,

mutations in the gene encoding MCP (CD46) were identified

in three families (Richards et al, 2003). Since then, more than

20 additional mutations in MCP have been described in aHUS

(Noris et al, 2003; Esparza-Gordillo et al, 2005; Caprioli et al,

2006; Fremeaux-Bacchi et al, 2006; Richards et al, 2007a).

Mutations in MCP are present in 10–13% of aHUS patients

(Caprioli et al, 2006) (Table I). A majority of the mutations

are heterozygous, with c. 25% being either homozygous or

compound heterozygotes (Richards et al, 2007a). Most muta-

tions occur within the extracellular four repeating CCP

modules that house the sites for complement regulation

(Liszewski et al, 2005).

Two types of MCP mutations have been described (Richards

et al, 2007a; Saunders et al, 2007). The majority of mutants

(c. 75%) are type I mutants that have reduced cell surface

expression (Table I). The remaining c. 25% are type II

mutants in which MCP is expressed normally but has reduced

or absent complement regulatory activity. The functional

defect is therefore a decreased ability to inhibit the AP of

complement.

A characteristic feature of aHUS is reduced penetrance and

variable inheritance, suggesting that complement regulatory

proteins possess additional contributing genetic factors or may

act as modifiers (Esparza-Gordillo et al, 2005, 2006; Fremeaux-

Bacchi et al, 2005). A susceptibility factor in CD46, termed the

CD46ggaac SNP haplotype, contains SNPs in the CD46

promoter region that may reduce transcriptional activity in

reporter gene assays (Esparza-Gordillo et al, 2005).

Factor I. Factor I is a serum glycoprotein that provides

cofactor activity by cleaving the a¢ chains of C3b and C4b in

the presence of a cofactor protein, such as FH, MCP or C4bp

(Fig 2A). Mutations in CFI account for 3–13% of the

mutations in aHUS (Fremeaux-Bacchi et al, 2004; Esparza-

Gordillo et al, 2005; Kavanagh et al, 2005, 2008b; Caprioli

et al, 2006; Geelen et al, 2007; Goicoechea de Jorge et al,

2007; Sellier-Leclerc et al, 2007) (Table I). The CFI mutations

in aHUS are all heterozygous and are located throughout the

CFI gene. As in CD46- and CFH-associated aHUS,

incomplete penetrance is common (Esparza-Gordillo et al,

2006). Around 40% of these mutations result in low serum

levels of FI and a quantitative defect in complement

regulation (Kavanagh et al, 2007) (Table I). Functional

analyses of mutations residing in the serine protease

domain of FI have demonstrated a loss of cofactor activity

for C3b and C4b (Nilsson et al, 2007; Kavanagh et al, 2008b).

C4 binding protein (C4bp). Like FH, C4bp is an abundant

plasma complement regulatory protein. C4bp principally

controls C4b-mediated reactions (Blom et al, 2004),

however, in addition, C4bp acts as a cofactor for the

cleavage of C3b and therefore may contribute to regulation

of the AP, although not as strongly as FH (Blom et al, 2003). A

polymorphism in C4BPA/B which is a risk factor for the

development of aHUS has recently been described (Blom et al,

2008). This non-synonymous polymorphism (R240H)

demonstrated normal activity for C4b but reduced C3b

cofactor activity, particularly on the cell surface. This again

points to the importance of the AP in the pathogenesis of

aHUS.

Excessive complement activation

In addition to the loss of function mutations in the comple-

ment regulators described in aHUS above, gain of function

mutations have been shown to predispose to aHUS.

Factor B. Goicoechea de Jorge et al (2007) described mutations

in FB, the zymogen that carries the catalytic site of the

complement AP C3 convertase (C3bBb). Mutations in CFB are

rare, accounting for between 0% and 3% of the panels so far

examined (Kavanagh et al, 2006; Goicoechea de Jorge et al,

2007). As with the loss of function mutations in aHUS, the CFB

mutations exhibit incomplete penetrance. Functional analyses

of the two FB mutations described point to increased enzyme

activity in vivo in keeping with the low C3 serum levels seen in

these patients. The F286L mutant shows enhanced formation of

the C3bB proenzyme, while the K323E mutant forms a C3bBb

enzyme more resistant to decay by the complement regulators

DAF and FH (Goicoechea de Jorge et al, 2007).

C3. C3 is the central component of the complement pathways.

Activation of the classical, lectin or alternative pathway results

in cleavage of C3 to generate C3b and the anaphylatoxin C3a.

During generation of C3b, a highly reactive thioester bond is

broken, allowing this transiently reactive C3 fragment to attach

to any nearby target and serve as a nidus for complement

activation. When the target is a pathogen, amplification is, of

course, desirable. However, in the setting of impaired

regulation of C3, the outcome may be damaging to the

human cell on which it is deposited.

The clinical importance of a polymorphism in C3 has been

highlighted by several recent studies. A common non-

synonymous coding change in C3 (SNP rs2230199, Arg80Gly,

corresponding to allotypes C3S and C3F) was associated with

development of age-related macular degeneration (Maller et al,

2007; Yates et al, 2007) and with renal allograft survival

(Brown et al, 2006). The allelic frequency of these two

common variants is 0Æ80 (C3S) and 0Æ20 (C3F).

Heterozygous mutations in C3 have now been identified in

aHUS patients (Fremeaux-Bacchi et al, in press, 2008). In two

cohorts, patients with low C3 levels but without mutations in

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CFH, CFI, MCP or CFB (representing �10% of the patients)

were screened for mutations in C3. In 14 of 26 such patients,

nine distinct mutations (not observed in 200 controls) were

identified. Five of these mutations in C3 (R570Q, R570W,

A1072V, D1093N and Q1139K) led to impaired binding and

regulation by the native regulators MCP and, to a lesser degree,

CFH. Because these mutations prevent appropriate C3b

regulation, they result in a secondary gain of function. More

extensive screening for C3 mutations in aHUS patients is in

progress.

Clinical course and prognosis follow specificcomplement mutations

The elucidation of the genetic basis of aHUS has allowed the

classification of disease according to the predisposing muta-

tion. This reveals that those individuals with a CFH mutation

have a poor prognosis, with 70–80% developing end stage

renal failure (ESRF) or dying (Caprioli et al, 2006; Sellier-

Leclerc et al, 2007). Individuals with CFI mutations also have a

poor outlook, with 75% of published cases developing ESRF or

dying (Fremeaux-Bacchi et al, 2004; Kavanagh et al, 2005,

2008b; Caprioli et al, 2006; Geelen et al, 2007; Nilsson et al,

2007; Sellier-Leclerc et al, 2007). The few patients with CFB

mutations have developed ESRF (Goicoechea de Jorge et al,

2007). In contrast, MCP-aHUS tends to follow a more

relapsing/remitting course (one patient had 10 distinct

episodes) (Fremeaux-Bacchi et al, 2006). Even in the long

term, 70–80% of patients remain dialysis-free (Caprioli et al,

2006; Sellier-Leclerc et al, 2007).

Genotype–phenotype correlations are also observed after

renal transplantation. In those with mutations in the serum

complement regulators (CFH/CFI), disease recurrence and graft

failure are high (Bresin et al, 2006; Sellier-Leclerc et al, 2007). In

the only patient with a CFB mutation to undergo renal

transplantation, there was also recurrence of aHUS (Goicoechea

de Jorge et al, 2007). In patients with mutations in CD46, the

recurrence rate is lower, as MCP is a transmembrane regulator

and renal allografts will therefore be protected by wild-type MCP

from the donor (Bresin et al, 2006; Richards et al, 2007a; Sellier-

Leclerc et al, 2007). These differences in outcome following

transplantation have resulted in the European Working Party on

the Genetics of HUS recommending screening for mutations

prior to listing for renal transplantation (Kavanagh et al, 2007).

The HELLP syndrome

The HELLP syndrome complicates pregnancy. The early

diagnosis of HELLP is based on the detection of haemolysis,

altered liver function tests, and thrombocytopenia. It occurs

with an incidence of 0Æ2–0Æ6% of all pregnancies (Stella et al,

2008). The HELLP syndrome is characterized by prominent

endothelial cell damage within the liver instead of the kidney as

in aHUS. Hypovolemia is suggested with a decrease in the liver

blood flow on Doppler examination in patients with pre-

eclampsia, who have subsequently developed HELLP syn-

drome (Kawabata et al, 2006). Hepatic ischemia may cause

infarction, subcapsular haematomas and intraparenchymatous

haemorrhage, resulting in hepatic rupture, a rare but severe

complication that is associated with haemoperitoneum (O’Brien

& Barton, 2005). Recurrent episodes of hepatic haematoma and

rupture in subsequent pregnancies have been reported,

suggesting that there may be a specific predisposition to this

condition (Wust et al, 2004).

On liver biopsy, periportal haemorrhage, focal parenchy-

matous necrosis and macrovesicular steatosis may be observed

in up to 1/3 of patients. There is little correlation between the

histological findings and clinical presentation, however. Fibrin

and hyaline deposits are seen by immunofluorescence at the

level of liver sinusoids (Mihu et al, 2007).

Current hypotheses of HELLP pathogenesis

The pathogenesis of HELLP syndrome is not understood. One

hypothesis is an alteration in the maternal–fetal immune

balance induces platelet aggregation, endothelial dysfunction

and arterial hypertension. Because trophoblast invasion invari-

ably brings the fetus in contact with the immunocompetent

maternal cells, the HELLP syndrome can be considered an

acute maternal immune rejection of the genetically foreign

fetus (Mihu et al, 2007). Alternatively, increased platelet

plasminogen activation may play a role, as the levels of

plasminogen activator and plasminogen activator inhibitor-1

are increased in HELLP syndrome compared to normal

pregnancy (Zhou et al, 2002).

An inborn error of fatty acid oxidative metabolism may

occur in fetuses born in context of HELLP syndrome (Ibdah

et al, 1999). A mutation allows a long chain fatty acid, i.e. a

3-hydroxyacyl metabolite that is produced by the fetus and/or

the placenta, to accumulate at maternal level due to a long

chain 3-hydroxy-acyl coenzyme A dehydrogenase deficiency.

This results in an insufficient mitochondrial oxidation of fatty

acids required for ketogenesis, once the liver as a glycogen

source has been exhausted. An association with medium-chain

acyl-CoA dehydrogenase deficiency has also been reported

(Nelson et al, 2000).

Some believe that the HELLP syndrome is a placenta-

instigated, liver-targeted acute inflammatory condition. The

liver occupies a central role in the disorder of HELLP

syndrome and a major pathogenic mechanism for liver disease

is CD95 (APO-1, Fas)-mediated apoptosis of hepatocytes

(Martin et al, 2006). CD95 ligand was found to be produced in

the placenta. Extracts of placenta were cytotoxic for human

hepatocytes and cytotoxic activity increased as HELLP syn-

drome developed. Blocking of CD95 signalling reduced the

cytotoxic activity of HELLP serum and liver cell apoptosis

(Strand et al, 2004).

Controversy surrounds the issue of HELLP being a

separate disorder or a severe form of pre-eclampsia. As

many as 15–20% of HELLP patients do not have antecedent

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hypertension or proteinuria, the defining signs of pre-

eclampsia (Sibai, 2004). HELLP has been described as a

systemic inflammatory response syndrome (SIRS)-like

inflammatory form of severe pre-eclampsia (Martin et al,

2006). Pre-eclampsia complicates c. 3–5% of pregnancies

(Lynch et al, 2008). HELLP in turn develops in 4–14% of

women with severe pre-eclampsia (Sibai et al, 1995). If the

HELLP syndrome is a form of severe pre-eclampsia, it

probably has its origins in aberrant placental development

and ischemia-producing oxidative stress may trigger release

of factors that injure the systemic endothelium via activation

of platelets, vasoconstrictors, and loss of the normal

pregnancy vascular relaxation (Martin et al, 2006). These

changes induce platelet aggregation, microvascular narrow-

ing, endothelial dysfunction and arterial hypertension.

Complement and the HELLP syndrome

We recently reported on a 30-year-old Caucasian patient who

developed HELLP during her second pregnancy and then

chronic renal failure one year later (Fang et al, 2008). She had

a mutation in CD46 that corresponded to an alanine to valine

change at position 304 that is in the transmembrane region of

the protein. Only upon testing the mutation on the cell surface

(in situ) was a defect found (Fig 3). In enzyme-linked

immunosorbent assay and fluid phase experiments, no defect

in C3b binding or complement regulatory activity could be

detected (Fang et al, 2008).

Unfortunately, additional clinical details were not available

for this patient with a CD46 mutation and HELLP. Interest-

ingly, in contrast with the renal outcome of the patient just

described, renal dysfunction in the HELLP syndrome usually

recovers completely, responding to measures short of dialysis

or after a brief course of dialysis. The incidence of acute renal

dysfunction and/or failure in the HELLP syndrome has been

described in 8% to as high as 54% of cases (Abraham et al,

2001; Zhang et al, 2003). Significant renal injury is infre-

quently encountered in patients with HELLP syndrome unless

placental abruption or a major haemorrhage also occurs. Two

studies provide some long-term follow-up data of HELLP

syndrome patients. At a mean of 4Æ6 years of follow-up (range

0Æ5–11 years), renal function was not permanently impaired in

23 patients whose pregnancies were complicated with HELLP

syndrome and acute renal failure (Sibai & Ramadan, 1993). A

similar normalization of renal function after the HELLP

syndrome was reported by another group (Jacquemyn et al,

2004). In this series of 10 patients, renal function was

compared 5 years later to 22 patients with previous normo-

tensive gestation. There were no differences in renal function

tests between the two groups.

Other evidence supports a role for the complement system

in pre-eclampsia/HELLP. Elevated levels of the AP comple-

ment activation fragment Bb in the first 20 weeks of pregnancy

were independently associated with pre-eclampsia later in

pregnancy (Lynch et al, 2008). Women with severe pre-

eclampsia had increased levels of the anaphylatoxin C5a and

terminal C5b-9 as compared with uneventful pregnancies

(Haeger et al, 1990). More recently, complement activation

was shown to induce dysregulation of angiogenic factors in a

murine model of spontaneous miscarriage and intrauterine

growth restriction (Girardi et al, 2006). The soluble receptor

for vascular endothelial growth factor (VEGF)-1, also known

as sVEGFR-1 and sFlt1 (soluble fms-like tyrosine kinase 1),

binds vascular endothelial growth factors and placental growth

factor. Pre-eclamptic women have higher circulating sVEGFR-1

concentrations in their placenta and blood than do normal

pregnant control women (Levine et al, 2004). Placental

trophoblasts exposed to hypoxia release large amounts of

sVEGFR-1 into the maternal circulation (Maynard et al, 2003).

This trophoblast-derived factor has been shown to inhibit

placental cytotrophoblast differentiation and invasion and is

thought to play a direct role in the pathogenesis of abnormal

placental development associated with pre-eclampsia

(Charnock-Jones & Burton, 2000). Complement activation

products, particularly C5a, stimulate monocytes to produce

sVEGFR-1 and thereby sequester VEGF (Girardi et al, 2006).

The incidence of HELLP syndrome in the antiphospholipid

syndrome (APS)/catastrophic antiphospholipid syndrome

(CAPS) is difficult to estimate although approximately 50

cases have been documented (Gomez-Puerta et al, 2007).

HELLP appears in a more severe form in early stages of

Fig 3. A304V is defective in its capacity to control alternative com-

plement activation on the cell surface. The MCP mutation, A304V in

the transmembrane domain, is shared by multiple aHUS patients and a

HELLP syndrome patient. Using a model system, a functional defect in

A304V was observed on the cell surface when compared to wild type

(WT) in situ. Using conditions to activate the alternative pathway

(high levels of sensitizing anti-Chinese hamster ovary (CHO) antibody

and 10% serum), the A304V mutant (MFI 47) allowed more C3b

deposition than WT (MFI 24) and thus showed a reduced ability to

regulate complement activation. CHO cells without MCP (CHO MFI

310) are not protected from C3b deposition and used as a control.

Using a model system, a functional defect in A304V was observed on

the cell surface when compared to wild type (WT) in situ (Fang et al,

2008).

Review


pregnancy in patients with APS than in the general population

(Tsirigotis et al, 2007). Also, HELLP, when associated with

antiphospholipid (aPL) antibodies (Abs), may be more severe

as well as being refractory to standard treatment leading to the

development of hepatic infarcts (Asherson et al, 2008).

The role of the complement system in APS has been

investigated in murine models and recently reviewed (Salmon

& Girardi, 2008). A key observation is that inhibition of the

complement system protects against tissue damage and that

loss of complement regulatory activity enhances damage.

Using a mouse model of APS induced by passive transfer of

human aPL Abs, aPL Abs activate complement in the placenta,

generating split products that probably mediate placental

injury and lead to fetal loss and growth restriction (Holers

et al, 2002; Girardi et al, 2006). The complement activation by

aPL Abs in other vascular areas may cause inflammation and

thrombophilia. Mice deficient in C3 or C5 are less susceptible

to aPL Ab-induced thrombosis and endothelial cell activation.

Inhibiting C5 activation with an anti-C5 monoclonal antibody

prevents the thrombocytopenia that is induced by aPL Abs and

mice treated with other inhibitors of complement activation

are protected from fetal loss (Salmon & Girardi, 2008).

Complement and coagulation

If inadequately controlled, complement activation occurs in

aHUS and possibly HELLP. How does this lead to micro-

thrombi formation? The complement and coagulation systems

are linked through both direct and indirect interactions. The

endothelium itself and the vascular bed on which it resides

probably play an important role in this interaction.

The complement system contributes to thrombosis by

directly enhancing blood clotting properties. Incorporation

of the C5b-9 complex into the cell membrane activates

platelets and results in the exposure of procoagulant lipids

(Sims & Wiedmer, 1995). C3a and C5a induce platelet

activation and aggregation. Treating mast cells in vitro with

C5a causes an upregulation in PA inhibitor-1 that shifts the

balance in favour of procoagulant factors (Wojta et al, 2003).

C5a and the cytolytically inactive form of the MAC (sC5b-9)

induce tissue factor (TF) expression by leucocytes and human

endothelial cells (Markiewski et al, 2007).

Complement effectors contribute to changes in the endo-

thelium that augment the clotting properties of blood. C1q

binding and C5b-9 attachment induce upregulation of adhe-

sion molecules for platelets on endothelial cells (Tedesco et al,

1999). C5b-9 attachment induces the release of microparticles

that provide an extra surface for the assembly of a procoag-

ulant enzyme and acts as an inhibitor of endothelium-derived

vasorelaxing activity. Sublytic attack by C5b-9 induces release

of VWF, which favours platelet adherence to the vessel wall

(Tedesco et al, 1999). C5a causes release of heparan sulfate and

other GAGs from the plasma membranes of endothelial cells,

reducing the anticoagulant property of the endothelial surface

(Platt et al, 1991).

Complement also augments the thrombogenic properties of

blood by an indirect interaction. C4bp forms a complex with

Protein S (PS). This results in a loss of PS activity and decrease

in its anticoagulant effects. Binding of PS-C4bp complexes to

negatively charged phospholipids of cell membranes, mediated

through PS, localizes this complement inhibitor to the sites at

which coagulation is initiated (Rezende et al, 2004). C3a and

C5a contribute to the regulation of the cytokine response,

influencing production and secretion of tumour necrosis

factor-a (TNF-a) and interleukin-6 (IL-6) by macrophages

(Markiewski et al, 2007). In turn, TNF-a is a potent enhancer

of tissue factor (TF) expression by monocytes while IL-6

increases the production and thrombogenicity of platelets.

Inflammatory cytokines also decrease the level of several

anticoagulants (Shebuski & Kilgore, 2002).

A disruption of the endothelial cell lining by mechanical

or chemical stimuli may activate the complement system and

clotting. The focal nature of haemostatic control and thus

the thrombotic tendency of each organ varies depending on

the distribution of the anticoagulant and procoagulant

factors throughout its vascular tree (Rosenberg & Aird,

1999). This uneven distribution of such factors in the

coagulation system perhaps explains the tissue-specificity of

the kidney for aHUS and the liver for HELLP. For example,

the levels of VWF mRNA and VWF protein vary from

one vascular bed to another and there is heterogeneity in

the expression of components of the fibrinolytic pathway.

Endothelial cells from various vascular beds may also have

different responses to the same signals (Rosenberg & Aird,

1999). In patients with TTP, plasma has different effects on

endothelial cells from different organs. Apoptosis is increased

in endothelial cells from renal and cerebral vessels but not in

endothelial cells from the lungs or the liver (Mitra et al,

1997). These findings closely correlate with the distribution

of microthrombi in patients with TTP and suggest that the

phenotype is governed by individualistic responses of

endothelial cells to a stimulus.

The endothelium protects itself from complement attack by

releasing soluble complement regulators, such as FH and FI,

that inhibit the fluid phase complement activation and by

expressing surface molecules with complement inhibitory

activity. The expression of the membrane-bound complement

regulators DAF, MCP and CD59 protect endothelial cells.

Reduced control of complement activation (due to mutations

in FH, MCP and FI or gain of function mutations in FB and

C3) is thought to be responsible for the damage of the renal

endothelium in aHUS. Whether these mechanisms apply to the

liver injury seen in the HELLP syndrome remains to be

established.

Conclusion

Complement is a central mechanism contributing to aHUS

and possibly to HELLP. Although the cause of tissue injury

in these diseases is multifactorial, excessive activation or

Review


defective regulation of the complement system is important

in pathogenesis. Based on findings in aHUS, we propose a

similar mechanism for a pathogenetic role of complement in

pre-eclampsia/HELLP. In this scenario, the underlying

problem is defective complement regulation that allows for

excessive activation for a given degree of endothelial cell

injury. The susceptibility of the renal endothelium in aHUS

and the hepatic vessels in HELLP to damage, in the setting

of tendency to excessive complement activation, suggests

unique predisposing features and responses to injury.

Complement activation fragments induce procoagulant

activity that leads to thrombosis. Depending on the trigger-

ing stimuli and vascular bed involved, aHUS or the HELLP

syndrome may develop.

Acknowledgements

The authors thank our many collaborators in the HUS field,

especially Timothy H.J. Goodship, Veronique Fremeaux-

Bacchi, Marina Noris, Giuseppe Remuzzi and Howard Tracht-

man. This work was supported by National Institutes of Health

(NIH) grant no. T32 AR07279 (C.J.F.) and NIH grant RO1

AI37618 (M.K.L. and J.P.A.).

References

Abraham, K.A., Connolly, G., Farrell, J. & Walshe, J.J. (2001) The

HELLP syndrome, a prospective study. Renal Failure, 23, 705–713.

Alexander, J.J. & Quigg, R.J. (2007) The simple design of complement

factor H: looks can be deceiving. Molecular Immunology, 44, 123–

132.

Asherson, R.A., Glarza-Maldonado, C. & Sanin-Blair, J. (2008) The

HELLP syndrome, antiphospholipid antibodies, and syndromes.

Clinical Rheumatology, 27, 1–4.

Blom, A.M., Kask, L. & Dahlback, B. (2003) CCP1-4 of the C4b-

binding protein alpha-chain are required for factor I mediated

cleavage of complement factor C3b. Molecular Immunology, 39, 547–

556.

Blom, A.M., Villoutreix, B.O. & Dahlback, B. (2004) Functions of

human complement inhibitor C4b-binding protein in relation to its

structure. Archivum Immunologiae et Therapiae Experimentalis

(Warszawa), 52, 83–95.

Blom, A., Bergstrom, F., Edey, M., Diaz-Torres, M., Kavanagh, D.,

Lampe, A., Goodship, J.A., Strain, L., Moghal, N., McHugh, M.,

Inward, C., Tomson, C., Fremeaux-Bacchi, V. & Goodship, T.

(2008) A novel non-synonymous polymorphism (p.Arg240His) in

C4b-binding protein is associated with atypical hemolytic uremic

syndrome and leads to impaired alternative pathway cofactor

activity. Journal of Immunology, 180, 6385–6391.

Bresin, E., Daina, E., Noris, M., Castelletti, F., Stefanov, R., Hill, P.,

Goodship, T.H. & Remuzzi, G. (2006) Outcome of renal trans-

plantation in patients with non-Shiga toxin-associated haemolytic

syndrome: prognostic significance of genetic background. Clinical

Journal of the American Society of Nephrology, 1, 88–99.

Brown, K.M., Kondeatis, E., Vaughan, R.W., Kon, S.P., Farmer, C.K.,

Taylor, J.D., He, X., Johnston, A., Horsfield, C., Janssen, B.J., Gros,

P., Zhou, W., Sacks, S.H. & Sheerin, N.S. (2006) Influence of donor

C3 allotype on late renal-transplantation outcome. New England

Journal of Medicine, 354, 2014–2023.

Caprioli, J., Bettinaglio, P., Zipfel, P., Amadei, B., Daina, E., Gamba, S.,

Skerka, C., Marziliano, N., Remuzzi, G. & Noris, M. (2001) The

molecular basis of familial hemolytic uremic syndrome: mutation

analysis of factor H gene reveals a hot spot in short consensus repeat

20. Journal of the American Society of Nephrology, 12, 297–307.

Caprioli, J., Castelletti, F., Bucchioni, S., Bettinaglio, P., Bresin, E.,

Pianetti, G., Gamba, S., Brioschi, S., Daina, E., Remuzzi, G. & Noris,

M. (2003) Complement factor H mutations and gene polymor-

phisms in haemolytic uraemic syndrome: the C-257T, the A2089G

and the G2881T polymorphisms are strongly associated with disease.

Human Molecular Genetics, 12, 3385–3395.

Caprioli, J., Noris, M., Brioschi, S., Pianetti, G., Castelletti, F., Betti-

naglio, P., Mele, C., Bresin, E., Cassis, L., Gamba, S., Porrati, F.,

Bucchioni, S., Monteferrante, G., Fang, C.J., Liszewski, M.K., Kav-

anagh, D., Atkinson, J.P. & Remuzzi, G. (2006) Genetics of HUS: the

impact of MCP, CFH and IF mutations on clinical presentation,

response to treatment, and outcome. Blood, 108, 1267–1279.

Charnock-Jones, D.S. & Burton, G.J. (2000) Placental vascular mor-

phogenesis. Bailliere’s Best Practice and Research. Clinical Obstetrics

and Gynaecology, 14, 953–968.

Constantinescu, A.R., Bitzan, M., Weiss, L.S., Christen, E., Kaplan,

B.S., Cnaan, A. & Trachtman, H. (2004) Non-enteropathic hemo-

lytic uremic syndrome: causes and short-term course. American

Journal of Kidney Diseases, 43, 976–982.

Dragon-Durey, M.-A., Fremeaux-Bacchi, V., Loirat, C., Blouin, J.,

Niaudet, P., Deschenes, G., Coppo, P., Fridman, W. & Weiss, L.

(2004) Heterozygous and homozygous Factor H deficiencies asso-

ciated with hemolytic uremic syndrome or membranoproliferative

glomerulonephritis: report and genetic analysis of 16 cases. Journal

of the American Society of Nephrology, 15, 787–795.

Dragon-Durey, M., Loirat, C., Cloarec, S., Macher, M.A., Blouin, J.,

Nivet, H., Weiss, L., Fridman, W.H. & Fremeaux-Bacchi, V. (2005)

Anti-Factor H autoantibodies associated with atypical hemolytic

uremic syndrome. Journal of the American Society of Nephrology, 16,

555–563.

Esparza-Gordillo, J., Goicoechea de Jorge, E., Buil, A., Carreras Berges,

L., Lopez-Trascasa, M., Sanchez-Corral, P. & Rodriguez de Cordoba,

S. (2005) Predisposition to atypical hemolytic uremic syndrome

involves the concurrence of different susceptibility alleles in the

regulators of complement activation gene cluster in 1q32. Human

Molecular Genetics, 14, 703–712. [CORRIGENDUM. Human

Molecular Genetics, 14, 1107].

Esparza-Gordillo, J., Goicoechea de Jorge, E., Garrido, C., Carreras, L.,

Lopez-Trascasa, M., Sanchez-Corral, P. & Rodriguez de Cordoba, S.

(2006) Insights into hemolytic uremic syndrome: segregation of

three independent predisposition factors in a large, multiple affected

pedigree. Molecular Immunology, 43, 1769–1775.

Fang, C.J., Fremeaux-Bacchi, V., Liszewski, M.K., Pianetti, G., Noris,

M., Goodship, T.H. & Atkinson, J.P. (2008) Membrane cofactor

protein mutations in atypical hemolytic uremic syndrome, fatal Stx-

HUS, C3 glomerulonephritis, and the HELLP syndrome. Blood, 111,

624–632.

Fremeaux-Bacchi, V., Dragon-Durey, M.-A., Blouin, J., Vigneau, C.,

Kuypers, D., Boudailliez, B., Loirat, C., Rondeau, E. & Fridman,

W. (2004) Complement factor I: a susceptibility gene for atypical

haemolytic uraemic syndrome. Journal of Medical Genetics, 41,

e84.

Review


Fremeaux-Bacchi, V., Kemp, E., Goodship, J., Dragon-Durey, M.,

Strain, L., Loirat, C., Deng, H. & Goodship, T. (2005) The

development of atypical HUS is influenced by susceptibility fac-

tors in factor H and membrane cofactor protein - evidence from

two independent cohorts. Journal of Medical Genetics, 42, 852–

856.

Fremeaux-Bacchi, V., Moulton, E.A., Kavanagh, D., Dragon-Durey,

M.A., Blouin, J., Caudy, A., Arzouk, N., Cleper, R., Francois, M.,

Guest, G., Pourrat, J., Seligman, R., Fridman, W.H., Loirat, C. &

Atkinson, J.P. (2006) Genetic and functional analyses of membrane

cofactor protein (CD46) mutations in atypical hemolytic uremic

syndrome. Journal of the American Society of Nephrology, 17, 2017–

2025.

Fremeaux-Bacchi, V., Miller, E., Liszewski, M.K., Strain, L., Blouin, J.,

Brown, A.L., Moghal, N., Kaplan, B.S., Weiss, R.A., Lhotta, K.,

Kapur, G., Mattoo, T., Nivet, H., Wong, W., Gie, S., de Ligny, B.H.,

Fischbach, M., Gupta, R., Hauhart, R., Meunier, V., Loirat, C.,

Dragon-Durey, M.-A., Fridman, W.H., Janssen, B.J.C., Goodship,

T.H.J. & Atkinson, J.P. (2008) Mutations in complement C3 pre-

dispose to development of atypical hemolytic uremic syndrome.

Blood, In press.

Geelen, J., van den Dries, K., Roos, A., van de Kar, N., de Kat Angelino,

C., Klasen, I., Monnens, L. & van den Heuvel, L. (2007) A missense

mutation in factor I (IF) predisposes to atypical haemolytic uraemic

syndrome. Pediatric Nephrology, 22, 371–375.

George, J.N. (2003) The association of pregnancy with thrombotic

thrombocytopenic purpura-hemolytic uremic syndrome. Current

Opinion in Hematology, 10, 339–344.

Girardi, G., Yarilin, D., Thurman, J.M., Holers, V.M. & Salmon, J.E.

(2006) Complement activation induces dysregulation of angiogenic

factors and causes fetal rejection and growth restriction. Journal of

Experimental Medicine, 203, 2165–2175.

Goicoechea de Jorge, E., Harris, C.L., Esparza-Gordillo, J., Carreras, L.,

Arranz, E.A., Garrido, C.A., Lopez-Trascasa, M., Sanchez-Corral, P.,

Morgan, B.P. & Rodriguez de Cordoba, S. (2007) Gain of function

mutations in complement factor B are associated with atypical

hemolytic uremic syndrome. Proceedings of the National Academy of

Sciences of the United States of America, 104, 240–245.

Gomez-Puerta, J.A., Cervera, R., Espinosa, G., Asherson, R.A., Garcia-

Carrasco, M., da Costa, I.P., Andrade, D.C.O., Borba, E.F., Mak-

atsaria, A., Bucciarelli, S., Ramos-Casals, M. & Font, S. (2007)

Catastrophic antiphospholipid syndrome during pregnancy and

puerperium: maternal and fetal characteristics of 15 cases. Annals of

the Rheumatic Diseases, 66, 740–746.

Haeger, M., Unander, M. & Bengtsson, A. (1990) Enhanced anaphy-

latoxin and terminal C5b-9 complement complex formation

in patients with the syndrome of hemolysis, elevated liver

enzymes, and low platelet count. Obstetrics and Gynecology, 76, 698–

702.

Heinen, S., Sanchez-Corral, P., Jackson, M., Strain, L., Goodship, J.,

Kemp, E., Skerka, C., Jokiranta, T., Meyers, K., Wagner, E., Robi-

taille, P., Esparza-Gordillo, J., Rodriguez de Cordoba, S., Zipfel, P. &

Goodship, T. (2006) De novo gene conversion in the RCA gene

cluster (1q32) causes mutations in complement factor H associated

with atypical hemolytic uremic syndrome. Human Mutation, 27,

292–293.

Hellwage, J., Jokiranta, T., Koistinen, V., Vaarala, O., Meri, S. &

Zipfel, P. (1999) Functional properties of complement factor

H-related proteins FHR3 and FHR4: binding to the C3d region of

C3b and differential regulation by heparin. FEBS Letters, 462,

345–352.

Herbert, A., Uhrin, D., Lyon, M., Pangburn, M. & Barlow, P. (2006)

Disease-associated sequence variations congregate in a polyanion-

recognition patch on human factor H revealed in 3D structure.

Journal of Biological Chemistry, 281, 16512–16520.

Hocking, H.G., Herbert, A.P., Kavanagh, D., Soares, D.C., Ferreira,

V.P., Pangburn, M.K., Uhrin, D. & Barlow, P.N. (2008) Structure of

the N-terminal region of complement factor H and conformational

implications of disease-linked sequence variations. Journal of Bio-

logical Chemistry, 283, 9475–9487.

Holers, V.M., Girardi, G., Mo, L., Guthridge, J.M., Molin, H., Pier-

angeli, S.S., Espinola, R., Xiaowei, L.E., Mao, D., Vialpando, C.G. &

Salmon, J.E. (2002) Complement C3 activation is required for

antiphospholipid antibody-induced fetal loss. Journal of Experi-

mental Medicine, 195, 211–220.

Ibdah, J.A., Bennet, M.J., Rinaldo, P., Zhao, Y., Gibson, B., Sims, H.F.

& Strauss, A.W. (1999) A fetal fatty-acid oxidation disorder as a

cause of liver disease in pregnant women. New England Journal of

Medicine, 340, 1723–1731.

Jacquemyn, Y., Jochems, L., Duiker, E., Bosmans, J.L., Van Hoof, V. &

Van Campenhout, C. (2004) Long-term renal function after

HELLP syndrome. Gynecologic and Obstetric Investigation, 57, 117–

120.

Jokiranta, T., Cheng, Z., Seeberger, H., Jozsi, M., Heinen, S., Noris, M.,

Remuzzi, G., Ormsby, R., Gordon, D., Meri, S., Hellwage, J. &

Zipfel, P. (2005) Binding of complement factor H to endothelial

cells is mediated by the carboxyl-terminal glycosaminoglycan

binding site. American Journal of Pathology, 167, 1171–1181.

Jokiranta, T.S., Jaakola, V.-P., Lehtinen, M., Parepalo, M., Meri, S. &

Goldman, A. (2006) Structure of complement factor H carboxyl-

terminus reveals molecular basis of atypical haemolytic uremic

syndrome. Embo Journal, 25, 1784–1794.

Jozsi, M., Heinen, S., Hartmann, M., Ostrowicz, C., Halbich, S.,

Richter, H., Kunert, A., Licht, C., Saunders, R., Perkins, S., Zipfel, P.

& Skerka, C. (2006) Factor H and atypical hemolytic uremic syn-

drome: mutations in the C-terminus cause structural changes and

defective recognition functions. Journal of the American Society of

Nephrology, 17, 170–177.

Jozsi, M., Strobel, S., Dahse, H.M., Liu, W.S., Hoyer, P.F., Oppermann,

M., Skerka, C. & Zipfel, P.F. (2007) Anti factor H autoantibodies

block C-terminal recognition function of factor H in hemolytic

uremic syndrome. Blood, 110, 1516–1518.

Jozsi, M., Licht, C., Strobel, S., Zipfel, S.L., Richter, H., Heinen, S.,

Zipfel, P.F. & Skerka, C. (2008) Factor H autoantibodies in atypical

hemolytic uremic syndrome correlate with CFHR1/CFHR3 defi-

ciency. Blood, 111, 1512–1514.

Kavanagh, D., Kemp, E., Mayland, E., Winney, R., Duffield, J., War-

wick, G., Richards, A., Ward, R., Goodship, J. & Goodship, T. (2005)

Mutations in complement factor I (IF) predispose to the develop-

ment of atypical HUS. Journal of the American Society of Nephrology,

16, 2150–2155.

Kavanagh, D., Kemp, E., Richards, A., Burgess, R., Mayland, E.,

Goodship, J. & Goodship, T. (2006) Does complement factor B have

a role in the pathogenesis of atypical HUS? Molecular Immunology,

43, 856–859.

Kavanagh, D., Richards, A., Fremeaux-Bacchi, V., Noris, M., Good-

ship, J.A., Remuzzi, G. & Atkinson, J.P. (2007) Screening for com-

plement system abnormalities in patients with atypical hemolytic

Review


uremic syndrome. Clinical Journal of the American Society of

Nephrology, 2, 591–596.

Kavanagh, D., Richards, A. & Atkinson, J.P. (2008a) Complement

regulatory genes and hemolytic uremic syndromes. Annual Review of

Medicine, 59, 293–309.

Kavanagh, D., Richards, A., Noris, M., Hauhart, R., Liszewski, M.K.,

Karpman, D., Goodship, J.A., Fremeaux-Bacchi, V., Remuzzi, G.,

Goodship, T.H. & Atkinson, J.P. (2008b) Characterization of

mutations in complement factor I (CFI) associated with hemolytic

uremic syndrome. Molecular Immunology, 45, 95–105.

Kawabata, I., Nakai, A. & Takeshita, T. (2006) Prediction of HELLP

syndrome with assessment of maternal dual hepatic blood supply by

using Doppler ultrasound. Archives of Gynecology and Obstetrics,

274, 303–309.

Levine, R.J., Maynard, S.E., Qian, C., Lim, K.H., England, L.J., Yu, K.F.,

Schisterman, E.F., Thadhani, R., Sachs, B.P., Epstein, F.H., Sibai,

B.M., Sukhatme, V.P. & Karumanchi, S.A. (2004) Circulating

angiogenic factors and the risk of preeclampsia. New England

Journal of Medicine, 350, 672–683.

Liszewski, M.K., Kemper, C., Price, J.D. & Atkinson, J.P. (2005)

Emerging roles and new functions of CD46. Springer Seminars in

Immunopathology, 27, 345–358.

Lynch, A.M., Murphy, J.R., Byers, T., Gibbs, R.S., Neville, M.C., Giclas,

P.C., Salmon, J.E. & Holers, V.M.. (2008) Alternative complement

pathway activation fragment Bb in early pregnancy as a predictor of

preeclampsia. American Journal of Obstetrics and Gynecology, 198,

385 e1-385.e9.

Maller, J.B., Fagerness, J.A., Reynolds, R.C., Neale, B.M., Daly, M.J. &

Seddon, J.M. (2007) Variation in complement factor 3 is associated

with risk of age-related macular degeneration. Nature Genetics, 39,

1200–1201.

Manuelin, T., Hellwage, J., Meri, S., Capriolo, J., Noris, M., Heinen, S.,

Jozsi, M., Neumann, H., Remuzzi, G. & Zipfel, P. (2003) Mutations

in factor H reduce binding affinity to C3b and heparin and surface

attachment to endothelial cells in haemolytic uraemic syndrome.

Journal of Clinical Investigation, 111, 1181–1190.

Markiewski, M.M., Nilsson, B., Ekdahl, K.N., Mollnes, T.E. & Lambris,

J.D. (2007) Complement and coagulation: strangers or partners in

crime. TRENDS in Immunology, 28, 184–192.

Martin, J.N., Rose, C.H. & Briery, C.M. (2006) Understanding and

managing HELLP syndrome: the integral role of aggressive gluco-

corticoids for mother and child. American Journal of Obstetrics and

Gynecology, 195, 914–934.

Maynard, S.E., Min, J., Merchan, J., Lim, K.H., Li, J., Mondal, S.,

Libermann, T.A., Morgan, J.P., Sellke, F.W., Stillman, I.E., Epstein,

F.H., Sukhatme, V.P. & Karumanchi, S.A. (2003) Excess placental

soluble fms-like tyrosine kinase 1 (sFlt1) may contribute to endo-

thelial dysfunction, hypertension, and proteinuria in preeclampsia.

Journal of Clinical Investigation, 111, 649–658.

Mihu, D., Costin, M., Mihu, C.M., Seicean, A. & Ciortea, R. (2007)

HELLP Syndrome – a multisystemic disorder. Journal of Gastro-

intestinal and Liver Diseases, 16, 419–424.

Mitra, D., Jaffe, E.A., Weksler, B., Hajjar, K.A., Soderland, C. & Lau-

rence, J. (1997) TTP and sporadic HUS plasmas induce apoptosis in

restricted lineages of human microvascular endothelial cells. Blood,

89, 1224–1234.

Nelson, J., Lewis, B. & Walters, B. (2000) The HELLP syndrome

associated with fetal medium-chain acyl-CoA dehydrogenase defi-

ciency. Journal of Inherited Metabolic Diseases, 23, 518–519.

Neumann, H., Salzmann, H., Bohnert-Iwan, B., Manuelin, T., Skerka,

C., Lenk, D., Bender, B., Cybulla, M., Riegler, P., Konigsrainer, A.,

Neyer, U., Bock, A., Widmer, U., Franke, G. & Zipfel, P.F. (2003)

Haemolytic uraemic syndrome and mutations of the factor H gene:

a registry based study of German speaking countries. Journal of

Medical Genetics, 40, 676–681.

Nilsson, S., Karpman, D., Vaziri-Sani, F., Kristoffersson, A., Salomon,

R., Provot, F., Fremeaux-Bacchi, V., Trouw, L. & Blom, A. (2007) A

mutation in factor I that is associated with atypical haemolytic

uraemic syndrome does not affect the function of factor I in com-

plement regulation. Molecular Immunology, 44, 1845–1854.

Noris, M. & Remuzzi, G. (2005) Non-shiga toxin-associated hemolytic

uremic syndrome. In: Complement and Kidney Disease (ed. by P.

Zipfel), pp. 65–83. Birkhauser Verlag, Basel.

Noris, M., Brioschi, S., Caprioli, J., Todeschini, M., Bresin, E., Porrati,

F., Gamba, S. & Remuzzi, G. (2003) Familial haemolytic uraemic

syndrome and an MCP mutation. Lancet, 362, 1542–1547.

O’Brien, J.M. & Barton, J.R. (2005) Controversies with the diagnosis

and management of HELLP syndrome. Clinical Obstetrics and


Perez-Caballero, D., Gonzalez-Rubio, C., Gallardo, M., Vera, M.,

Lopez-Trascasa, M., Rodriguez de Cordoba, S. & Sanchez-Corral, P.

(2001) Clustering of missense mutations in the C-terminal region of

factor H in atypical hemolytic uremic syndrome. American Journal

of Human Genetics, 68, 478–484.

Pickering, M., Goicoechea de Jorge, E., Martinez-Barricarte, R.,

Recalde, S., Garcia-Layana, A., Rose, K., Moss, J., Walport, M.,

Cook, H.T., Rodriguez de Cordoba, S. & Botto, M. (2007) Spon-

taneous hemolytic uremic syndrome triggered by complement factor

H lacking surface recognition domains. Journal of Experimental

Medicine, 204, 1249–1256.

Platt, J.L., Dalmasso, A.P., Lindman, B.J., Ihrcke, N.S. & Bach, F.H.

(1991) The role of C5a and antibody in the release of heparan sulfate

from endothelial cells. European of Journal Immunology, 21, 2887–

2890.

Rezende, S.M., Simmonds, R.E. & Lane, D.A. (2004) Coagulation,

inflammation, and apoptosis: different role for protein S and the

protein S-C4b binding protein complex. Blood, 103, 1192–1201.

Richards, A., Buddles, M., Donne, R., Kaplan, B., Kirk, E., Venning,

M., Tielemans, C., Goodship, J. & Goodship, T. (2001) Factor H

mutations in hemolytic uremic syndrome cluster in exons 18-20, a

domain important for host cell recognition. American Journal of

Human Genetics, 68, 485–490.

Richards, A., Kemp, E.J., Liszewski, M.K., Goodship, J.A., Lampe, A.K.,

Decorte, R., Muslumanoglu, M.H., Kavukcu, S., Filler, G., Pirson, Y.,

Wen, L.S., Atkinson, J.P. & Goodship, T.H. (2003) Mutations in

human complement regulator, membrane cofactor protein (CD46),

predispose to development of familial hemolytic uremic syndrome.

Proceedings of the National Academy of Sciences of the United States of

America, 100, 12966–12971.

Richards, A., Liszewski, M.K., Kavanagh, D., Fang, C.J., Moulton, E.,

Fremeaux-Bacchi, V., Remuzzi, G., Noris, M., Goodship, T.H. &

Atkinson, J.P. (2007a) Implications of the initial mutations in

membrane cofactor protein (MCP; CD46) leading to atypical

hemolytic uremic syndrome. Molecular Immunology, 44, 111–122.

Richards, A., Kavanagh, D. & Atkinson, J. (2007b) Inherited comple-

ment regulatory protein deficiency predisposes to human diseases in

acute injury and chronic inflammatory states. Advances in Immu-

nology, 96, 139–175.

Review


Rock, G.A., Shumak, K.H., Buskard, N.A., Blanchette, V.S., Kelton,

J.G., Nair, R.C. & Spasoff, R.A. (1991) Comparison of plasma

exchange with plasma infusion in the treatment of thrombotic

thrombocytopenic purpura. Canadian Apheresis Study Group. New

England Journal of Medicine, 325, 393–397.

Rosenberg, R.D. & Aird, W.C. (1999) Vascular-bed-specific hemostasis

and hypercoagulable states. New England Journal of Medicine, 340,

1555–1564.

Salmon, J.E. & Girardi, G. (2008) Antiphospholipid antibodies and

pregnancy loss: a disorder of inflammation. Journal of Reproductive

Immunology, 77, 51–56.

Sanchez-Corral, P., Perez-Caballero, D., Huarte, O., Simckes, A.,

Goicoechea, E., Lopez-Trascasa, M. & Rodriguez de Cordoba, S.

(2002) Structural and functional characterization of factor H

mutations associated with atypical haemolytic uraemic syndrome.

American Journal of Human Genetics, 71, 1285–1295.

Sanchez-Corral, P., Gonzalez-Rubio, C., Rodriguez de Cordoba, S. &

Lopez-Trascasa, M. (2004) Functional analysis in serum from

atypical hemolytic uremic syndrome patients reveals impaired pro-

tection of host cells associated with mutations in factor H. Molecular

Immunology, 41, 81–84.

Saunders, R.E., Abarrategui-Garrido, C., Fremeaux-Bacchi, V., Goi-

coechea de Jorge, E., Goodship, T.H., Lopez Trascasa, M., Noris, M.,

Ponce Castro, I.M., Remuzzi, G., Rodriguez de Cordoba, S., San-

chez-Corral, P., Skerka, C., Zipfel, P.F. & Perkins, S.J. (2007) The

interactive factor H-atypical hemolytic uremic syndrome mutation

database and website: update and integration of membrane cofactor

protein and factor I mutations with structural models. Human

Mutation, 28, 222–234.

Sellier-Leclerc, A.L., Fremeaux-Bacchi, V., Dragon-Durey, M.A.,

Macher, M.A., Niaudet, P., Guest, G., Boudailliez, B., Bouissou, F.,

Deschenes, G., Gie, S., Tsimaratos, M., Fischbach, M., Morin, D.,

Nivet, H., Alberti, C. & Loirat, C. (2007) Differential impact of

complement mutations on clinical characteristics in atypical

hemolytic uremic syndrome. Journal of the American Society of

Nephrology, 18, 2392–2400.

Shebuski, R.J. & Kilgore, K.S. (2002) Role of inflammatory mediators

in thrombogenesis. Journal of Pharmacology and Experimental

Therapeutics, 300, 729–735.

Sibai, B.M. (2004) Diagnosis, controversies, and management of the

syndrome of hemolysis, elevated liver enzymes, and low platelet

count. Obstetrics and Gynecology, 103, 981–991.

Sibai, B.M. (2007) Imitators of severe preeclampsia. Obstetrics and


Sibai, B.M. & Ramadan, M.K. (1993) Acute renal failure in pregnancies

complicated by hemolysis, elevated liver enzymes, and low platelets.

American Journal of Obstetrics and Gynecology, 168, 1682–1687.

Sibai, B.M., Ramadan, M.K., Chari, R.S. & Friedman, S.A. (1995)

Pregnancies complicated by HELLP syndrome: subsequent preg-

nancy outcome and long-term prognosis. American Journal of

Obstetrics and Gynecology, 172, 125–129.

Sims, P.J. & Wiedmer, T. (1995) Induction of cellular procoagulant

activity by the membrane attack complex of complement. Seminars

in Cell Biology, 6, 275–282.

Stella, C.L., Malik, K.M. & Sibai, B.M. (2008) HELLP syndrome: an

atypical presentation. American Journal of Obstetrics and Gynecology,

198, e6–e8.

Strand, S., Strand, D., Seufert, R., Mann, A., Lotz, J., Blessing, M.,

Lahn, M., Wunsch, A., Broering, D.C., Hahn, U., Grischke, E.,

Rogiers, X., Otto, G., Gores, G.J. & Galle, P. (2004) Placenta-derived

CD95 ligand causes liver damage in hemolysis, elevated liver

enzymes, and low platelet count syndrome. Gastroenterology, 126,

849–858.

Tarr, P., Gordon, C. & Chandler, W. (2005) Shiga-toxin-producing

Escherichia coli and haemolytic uraemic syndrome. Lancet, 365,

1073–1086.

Tedesco, F., Fischetti, F., Pausa, M., Dobrina, A., Sim, R.B. & Daha,

M.R. (1999) Complement-endothelial cell interactions: pathophys-

iological implications. Molecular Immunology, 36, 261–268.

Tsai, H. (2006) Current concepts in thrombotic thrombocytopenic

purpura. Annual Review of Medicine, 57, 419–436.

Tsirigotis, P., Mantzios, G., Pappa, V., Girkas, K., Salamalekis, G.,

Koutras, A., Giannopoulou, V., Spirou, K., Balanika, A., Papageor-

giou, S., Travlou, A. & Dervenoulas, J. (2007) Antiphospholipid

syndrome: a predisposing factor for early onset HELLP syndrome.

Rheumatology International, 28, 171–174.

Vaziri-Sani, F., Holmberg, L., Sjoholm, A., Kristoffersson, A., Manea,

M., Fremeaux-Bacchi, V., Fehrman-Ekholm, I., Raafar, R. & Karp-

man, D. (2006) Phenotypic expression of factor H mutants in

patients with atypical hemolytic uremic syndrome. Kidney Interna-

tional, 69, 981–988.

Venables, J.P., Strain, L., Routledge, D., Bourn, D., Powell, H.M.,

Warwicker, P., Diaz-Torres, M.L., Sampson, A., Mead, P., Webb,

M., Pirson, Y., Jackson, M.S., Hughes, A., Wood, K.M., Goodship,

J.A. & Goodship, T.H. (2006) Atypical haemolytic syndrome

associated with a hybrid complement gene. PLoS Medicine, 3,

e431.

Veyradier, A., Obert, B., Haddad, E., Cloarec, S., Nivet, H., Foulard,

M., Lesure, F., Delattre, P., Lakhdari, M., Meyer, D., Girma, J. &

Loriat, C. (2003) Severe deficiency of the specific von willebrand

factor-cleaving protease (ADAMTS13) activity in a subgroup of

children with atypical hemolytic uremic syndrome. Journal of

Pediatrics, 142, 310–317.

Vik, D.P., Munoz-Canoves, P., Kozono, H., Martin, L.G., Tack, B.F. &

Chaplin, D.D. (1990) Identification and sequence analysis of four

complement factor H-related transcripts in mouse liver. Journal of

Biological Chemistry, 265, 3193–3201.

Warwicker, P., Goodship, T.H., Donne, R.L., Pirson, Y., Nicholls, A.,

Ward, R.M., Turnpenny, P. & Goodship, J.A. (1998) Genetic studies

into inherited and sporadic hemolytic uremic syndrome. Kidney

International, 53, 836–844.

Wojta, J., Huber, K. & Valent, P. (2003) New aspects in thrombotic

research: complement induced switch in mast cells from a profi-

brinolytic to a prothrombotic phenotype. Pathophysiology of Hae-

mostasis and Thrombosis, 33, 438–441.

Wust, M.D., Bolte, A.C., de Vries, J.I., Dekker, G.A., Cuesta, M.A. &

van Geijn, H.P. (2004) Pregnancy outcome after previous pregnancy

complicated by hepatic rupture. Hypertension in Pregnancy, 23, 29–

35.

Yates, J.R., Sepp, T., Matharu, B.K., Khan, J.C., Thurlby, D.A., Shahid,

H., Clayton, D.G., Hayward, C., Morgan, J., Wright, A.F., Armbr-

echt, A.M., Dhillon, B., Deary, I.J., Redmond, E., Bird, A.C. & Moor,

A.T. (2007) Complement C3 variant and the risk of age-related

macular degeneration. New England Journal of Medicine, 357, 553–

561.

Zhang, J., Meikle, S. & Trumble, A. (2003) Severe maternal morbidity

associated with hypertensive disorders in pregnancy in the United

States. Hypertension in Pregnancy, 22, 203–212.

Review


Zheng, X.L. & Sadler, J.E. (2008) Pathogenesis of thrombotic micro-

angiopathies. Annual Review of Pathology, 3, 249–277.

Zhou, Y., McMaster, M., Woo, K., Janatpour, M., Perry, J., Karpanen,

T., Alitalo, K., Damsky, C. & Fisher, S.J. (2002) Vascular endothelial

growth factor ligands and receptors that regulate human cyto-

trophoblast survival are dysregulated in severe preeclampsia and

hemolysis, elevated liver enzymes, and low platelets syndrome.

American Journal of Pathology, 160, 1405–1423.

Zipfel, P.F., Edey, M., Heinen, S., Jozsi, M., Richter, H., Misselwitz, J.,

Hoppe, B., Routledge, D., Strain, L., Hughes, A., Goodship, J.A.,

Licht, C., Goodship, T.H.J. & Skerka, C. (2007) Deletion of com-

plement factor H-related genes CFHR1 and CFHR3 is associated

with atypical hemolytic uremic syndrome. PLoS Genetics, 16, e41.

Review


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Advances in understanding of pathogenesis of aHUS and HELLP

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