Disorders of Platelet Adhesion

8/11/2019 Disorders of Platelet Adhesion

1/42

DISORDERS OF PLATELET ADHESION

PRESENTED BY

Dr. KHADIJA HABIB

M.Phil HAEMATOLOGY

1stSEMESTER


2/42

INTRODUCTION

Clinical bleeding results from disturbance in haemostasis.

The term haemostasis applies to myriad of physiological

processes that are involved in maintaining vascular integrity

and keeping the blood in fluid form.

Normal haemostasis involves interaction between 3 forces :

1. Vessel wall

2. Circulatory blood platelets

3. Co-agulation proteins


3/42


4/42

ROLEOFPLATELETSINNORMAL

HAEMOSTASIS

Normal haemostasis involves two stages

1. Primary stage : platelet plug formation

2. Secondary stage : strengthening of the plug by coagulation proteins

Platelets are responsible for primary haemostasis and carried

out in 4 steps:

1. Adhesion

2. Activation

3. Secretion4. Aggregation


5/42

ADHESION

Collagen

vWF

Dense granules (activation)= ADP, serotonin

Alpha granules (adhesion) = PF4, PDGF, vWF,fibrinogen

Gp Ib/IX/V


6/42

ACTIVATION

Collagen

vWF

Dense granules = ADP, serotonin

Alpha granules = PF4, PDGF, vWF, etcGp Ib/IX/VGpIa/IIa

GpIIb/IIa

Fibrinogen

GpIIb/IIIa conformational change

Induced with epinephrin, ADP, serotonin,

Arachidonic acid, thrombin


7/42

AGGREGATION

Collagen

vWF

Gp Ib/IX/VGpIa/IIaGpIIb/IIa

FibrinogenGpIIb/IIa

Fibrinogen

GpIIb/IIa

Fibrinogen

GpIIb/IIaFibrinogen

GpIIb/IIa

Fibrinogen

GpIIb/IIa

Fibrinogen

GpIIb/IIa

Fibrinogen


8/42

CLASSIFICATIONOFPLATELETDISORDERS

Disorders of Platelet number:

thrombocytopenia

thrombocytosis

Disorders of platelet functions


9/42

DISORDEROFPLATELETSFUNCTION

defects of platelet adhesion inherited: Bernard- Soulier syndrome , pseudo - VWD

acquired: uremia

defects of platelet aggregation inherited: Glantzmanns thrombasthenia

acquired: dysproteinemia, drug ingestion (ticlopidin)

defects of platelet release inherited: grey-platelet, Hermansky- Pudlak, Chediac-Higashi

syndrome.

acquired: cardiopulmonary bypass, myeloproliferative disorders,

drugs


10/42

THROMBOCYTOPATHIES

Platelets have a complex ultrastructure comprising amultitude of molecules and the malfunctioning of any of

these give rise to a specific disease.


11/42


12/42

DISORDERS OF PLATELET ADHESION


13/42

CLASSIFICATION

INHERITED

BernardSoulier syndrome

Platelet type VWD

ACQUIRED

uremia


14/42

MAJORPLATELETMEMBRANERECEPTORS

ANDTHEIRLIGANDS

Glycoprotein (GP)Receptor

Structure Function / Ligand

GP IIb / IIIa IntegrinIIb 3 Receptor forfibrinogen , vWF ,

fibronectin , vitronectin

and thrombospondin.

GP Ia / IIa Integrin 21 Receptor for collagen

GP Ib / IX / V Leucine rich repeatreceptors Receptor for insolubleVWF

GP VI Non-integrin receptor,

immunoglobulin

superfamily receptor.

Receptor for collagen


15/42

BERNARD

SOULIER SYNDROME


16/42

BSS

Is a bleeding disorder characterized by :

Abnormally large platelets ( giant platelet syndrome)

80% of platelets are usually larger than 2.5 um and often upto 8um

in diameter seen on PB film.

Mild or moderate thrombocytopeniaFrom as low as 20109/L to near normal

Number of BM megakaryocytes is usually normal.

Prolongation of skin bleeding time disproportionate to

thrombocytopenia

Number of BM megakaryocytes is usually normal.


17/42

Autosomal recessive disorder

Male : female = same

Parental history of similar bleeding problem is

absent

Consanguinity is common in reported kindreds

Rare disorder = 1 in 1 million population

Bleeding may be severe and fatal hemorrhages

may occur.


18/42

PATHOPHYSIOLOGY

The underlying biochemical defect is theabsence or decreased

expression of the glycoprotein Ib/IX/V complex on the surface

of the platelets. This complex is the receptor for vWF and the

result of decreased expression is deficient binding of vWF to the

platelet membrane at sites of vascular injury , resulting in

defective platelet adhesion. This is demonstrated by lack of

aggregation of platelets in response to Ristocetin. The end result

is lack of formation of primary platelet plug and increased bleeding

tendency. The cause of thrombocytopenia is not clearly known but

it is probably related to a decreased platelet life span.


19/42

MOLECULARBASISOFSYNDROME

The GPIbIXV receptor complex provides the principal site

mediating the interaction of platelets with the adhesive VWF.

This complex consists of four proteins:

the disulphide-linked - chain (135 kDa) and chain (25 kDa) of

GPIb

the non-covalently associated subunits GPIX (22 kDa) and GPV (82kDa).

They all share structural and functional features suggesting a

common evolutionary origin. Different transcripts encode the

four polypeptide chains and, with the exception of that of GPIb , genes show continuous (intron - depleted) open reading

frames.


20/42

All four genes encoding the complex have been cloned and 17

forms of BSS have to date been characterized at the

functional, immunological and molecular levels.

The mutations can be divided into two main groups.

Firstly, mutations located in Leucine rich repeats (LRR),

responsible for conformational modifications of the molecule, in

some cases higher sensitivity to proteases and loss of adhesive

function of the receptor, which is expressed at lower than normal

levels at the platelet membrane. When mutations affect the LRRof GPIba, the presence of the other chains varies from normal to

residual amounts. When mutations affect the LRR of GPIX,

expression of the other chains is strongly diminished, suggesting

that GPIX plays a major role in the stability of the complex

A second type of mutations leads to synthesis of a truncated

moleculelacking the transmembrane domain and absence of its

expression at the platelet surface, while the other chains are

present in residual amounts.

(Source : INSERM Unite 311, Etablissement de Transfusion Sanguine de

Strasbourg, France)


21/42

CLINICALPRESENTATION

Symptoms of BSS vary from 1 individual to other. Signs of the disorder

are usually first noticed during childhood.

Generally BSS manifest itself as :

Cutaneous hemorrhagesPurpura

Bruises

Epistaxis (may be difficult to control)

Bleeding from gums Heavy prolonged menstural bleeding (menorrhagia)

Bleeding after child birth

Haemarthrosis


22/42

Abnormal bleeding after

surgery

circumcision

dental work

Rarely vomiting blood / passing blood in stool due to

bleeding from gut

BSS cause more problem for women than for men

because of mensturation and child birth.


23/42

DIAGNOSTICAPPROACH


24/42

LABORATORYSTUDIES

CBC count:

Thrombocytopenia frequent finding but does vary

Giant platelets seen on peripheral smear

BT / PFA-100 closure time:

Neither BT nor PFA are good screening tests for platelet

function disorders as each has limited sensitivity (~40%)

even in symptomatic patient

BT & PFA-100 closure time is prolonged

Platelet Aggregation studies:

Platelets donot aggregate in response to ristocetin

Platelets have normal aggregation response to other

agonists like ADP, epinephrine, collagen, arachidonic

acid.


25/42


26/42


27/42

FLOW CYTOMETRY:

It is a technique used to measure protein expression on

the cell using monoclonal antibodies.

In BSS= decreased expression of GPIb/IX/V (CD42b)

FC may be normal with qualitative defects of CD42b


28/42

MANAGEMENT

Prevention and local care

Specific treatment options


29/42

PREVENTIONANDLOCALCARE

Avoid antiplatelet medications such as aspirin and non-

steroidal analgesics are critical

Fastidious dental hygiene with regular teeth cleaning

Hormonal control of the menstural bleeding(contraceptives)

Pre-surgical treatment plans should be part of comprehensivecare

Patient education about need to avoid trauma

Nasal packing etc for epistaxis

Gingival bleeding can be controlled by application of gel foam

soaked in tropical thrombin

For patients with moderate to severe symptoms, some

restriction of activity may be necessary


30/42

SPECIFICTREATMENTOPTIONS

ANTI-FIBRINOLYTIC AGENTS: These medications are useful for control of menorrhagia and other

mild bleeding manifestations from mucous membranes such as

epistaxis.

Epsilon amino caproic acid (EACA. Amicar)

Tranexamic acid

These can be used as mouth wash for local oral bleeding such as

from tonsillectomy sites or from dental extract.

DESMOPRESSIN ACETATE(DDAVP) Has been shown to shorten the bleeding time in some but not all

patients with BSS. It may be useful for minor bleeding episodes.

Exact mechanism is unknown but it may relate to increased levels

VWF binding to some residual GP 1b in patients without an absolute

deficiency.


31/42

PLATELET TRANSFUSION: Should be preserved for surgery / potentially life threatening

bleeding / other agents have failed

Patient may develop anti-platelet antibodies because of GP

Ib/IX/V , which are present on transfused platelets but absent

from the patients own platelets.

rF VII a (recombinant activated factor VII) Has been used in patients with BSS but very limited experience

use Exact mechanism of action is unknown, but it may work by

increasing thrombin generation and the deposition of fibrin at site

of vascular injury.


32/42

PSEUDO-VON WILLIBRAND DISEASE

(PLATELETTYPEVWD)

PSEUDO VWD


33/42

PSEUDO-VWD

Very rare Autosomal Dominant disorder

DEFECT :

Gain of function of platelet GPIb/IX/V complexresembles VWD

type 2B (adhesion disorder)

To date, four mutations have been identified within the GPIba gene.

1. Gly 233 Val (Miller et al, 1991;Russel and Roth 1993)

2. Met 239 Val (Takahashi et al., 1995)

3. Gly 233 Ser (Matsubara et al. 2003;Nurden et al., 2007)

4. 27bp deletion (Othman et al., 2005)

The disease is characterized by abnormally high binding affinity of the

platelets to the VWF, leading to a characteristic platelet hyperresponsiveness as evidenced by the ristocetin- induced platelet

agglutination (RIPA) test

(Miller et al., 1991) (Weiss et al., 1982).


34/42

BLEEDINGDIATHESIS

Two main mechanisms which lead to bleeding

diathesis:

1. Loss of HMW multimers due to their deposition on the platelet

surface

2. Thrombocytopenia caused by an increased removal of the bound

platelets

CLINICAL PRESENTATION:

Epistaxisecchymoses

menorrhagia

gingival hemorrhage


35/42

Pseudo-vWD (platelet-type) has similar clinical and laboratory

features to type 2B vWD; they are differentiated by vWF:PB

(platelet binding) assay (also called type 2B binding) or

molecular studies

Methods of discrimination include

RIPA mixing studies

Cryoprecipitate challenge

DNA analysis:

A1 domain (exon 28) VWF gene

Platelet GPIba gene


36/42

TREATMENTOFPLATELETTYPEVWD

The hyper-responsiveness of the platelet receptor results in

increased interaction with VWF in response to minimal or no

stimulation in vivo. This leads to a fall in plasma VWF and

typically to a decreased or low normal platelet count.

Replacement therapy in the form of VIII/VWF preparations or

drugs aiming at increasing the release of endogenous VWF

will exacerbate the condition and lead to further reduction of

the platelet count.

Ideal treatment would be:1. Infuse platelet concentrates

2. if possible a VIII/VWF preparation in a low enough dosage to

increase the haemostatic activity to a limit that does not induce a fall

in the platelet count (VWF:RCo of 40-47u/dl) (Miller 1996).


37/42

UREMIA


38/42

INTRODUCTION:

The bleeding tendency of patients with uremia is characterized

by hemorrhagic symptoms and by abnormal prolongation ofbleeding time. This bleeding tendency has been attributed

classically to abnormalities of platelet function that include

impaired adhesion [1] and decreased aggregation [1,2].

However, reports on various platelet functions in uremic patientshave been conflicting.

(1. Zwaginga JJ, Ijsseldijk MJW, de Groot PG, Vos J, de Bos Kuil RLJ, Sixma JJ. Defects in

platelet adhesion and aggregate formation in uraemic bleeding disorder can be attributedto factors in plasma. Arteriosclerosis Thromb 1991; 11: 733744)

(2. Mezzano D, Tagle R, Panes O et al. Hemostatic disorder of uremia: the platelet defect,

main determinant of the prolonged bleeding time, is correlated with indices of activation

of coagulation and fibrinolysis. Thromb Haemost 1996; 76: 312321)

STUDY: IMPAIRED EXPRESSION OF GLYCOPROTEINS ON


39/42

STUDY: IMPAIREDEXPRESSIONOFGLYCOPROTEINSONRESTINGANDSTIMULATEDPLATELETSINURAEMIC

PATIENTS(VALE RIEMOAL1, PHILIPPEBRUNET1, LAETITIADOU2, SOPHIEMORANGE3, JOSE SAMPOL2ANDYVONBERLAND1,3)IN2002.

The aim of this study was to assess bleeding tendency and to analyze

platelet surface GPs in uraemic patients.

The main findings were that:

(i) several subjects in the CRF and HD groups had bleeding symptoms

(ii) the bleeding time was longer in CRF and HD patients than in controls(iii) GPIb expression on resting platelets was lower in CRF

subjects than in controls, and this reduction correlated

with severity of renal failure

(iv) GPIIbIIIa expression on resting platelets was similar in CRF, HD and

controls

(v) GPIb expression on stimulated platelet was higher in HD than in

controls and CRF

(vi) GPIIbIIIa and P-selectin expression on stimulated platelets was lower

in CRF and HD than in controls.


40/42

Expression of platelet membrane glycoproteins in the basal state and in response to ADP and

TRAP in controls, CRF (chronic renal failure) and HD (haemodialysed) patients.

Moal V et al. Nephrol. Dial. Transplant. 2003;18:1834-1841

European Renal AssociationEuropean Dialysis and Transplant Association


41/42

Basal state GPIb expression was lower in CRF than in controls.

According to the literature, this decrease may be explained by four

mechanisms

a defect in protein synthesis, which is supported by the low total GPIb platelet

content reported in CRF [2]

loss of membrane protein by proteolytic cleavage may be due to the increased

plasmin and thrombin seen in uraemia [2]

Platelet activation after stimulation is usually followed by decreases in GPIb

expression because of its translocation to the canalicular system [16]

Uraemic toxins represent the fourth mechanism. [13]

(13. Kozek-Langenecker SA, Masaki T, Mohammad H, Green W, Mohammad SF, Cheung AK. Fibrinogen

fragments and platelet dysfunction in uremia. Kidney Int 1999; 56: 299-305)(16. Hourdille P, Heilmann E, Combrie R, Winckler J, Clemetson KJ, Nurden AT. Thrombin induces a

rapid redistribution of glycoprotein IbIX complexes within the membrane systems of activated human

platelets. Blood 1990;76: 15031513)


42/42

THANK YOU

Date post:	03-Jun-2018
Category:	Documents
Upload:	khadija-habib
View:	226 times
Download:	0 times

Disorders of Platelet Adhesion

Documents