Eric Niederhoffer, Ph.D.

SIU-SOM

Year Two ReviewPart 2

Outline

• Pyrimidine and purine synthesisincluding salvage and degradation

• Glycogen storage disorders

• Lysosomal storage disorders

• Heme synthesis and degradationincluding oxygen binding/unloading of heme

• Integration of metabolismincluding lipid synthesis/degradation, glycolysis/gluconeogenesis, TCA cycle and glycogenolysis/glycogen synthesis

Pyrimidine and Purine SynthesisHCO3

- + Gln

CP

CPSII

Asp

Oro

R5P

PRPP

RPK

UTP

TSN5,N10-mTHF

dTMP

DNARNA

dGTP dATPRR

GDP ADP

IMP

Gln

Gly

CO2

Asp

N10fTHFUMP

UMPS

CDP

dCDP

dUMP

Pyrimidine and Purine Salvage

U TPRPP

UMP TMP

RR

UTPT

GPRPP

HGPT

A

APT

X

XO

adenosine

inosineADA

HX

PNP

urateXO

UTP

CDP

dCDP

dUMP

TSN5,N10-mTHF

dTMP

RNA DNA

IMP

GDP ADP

dGTP dATPRR

Pathway Disorders

Rare autosomal recessive disorders• UMP synthase – deficiency in either orotate

phosphoribosyltransferase or OMP decarboxylase leads to hereditary orotic aciduria, megaloblastic anemia appearing weeks to months after birth that does not respond to cobalamin, folic acid, or iron, orotic crystalluria and nephropathy, cardiac malformations, strabismus, and recurrent infection. Urine orotic acid overexcretion. Enzyme assay of RBC. Treatment with oral uridine.

• Adenosine deaminase – (Severe combined immunodeficiency disorder) variety of clinical phenotypes, history of infections, diarrhea, dermatitis, and failure to thrive, ribs and vertebrae abnormalities (defects in cartilaginous structures). Lymphopenia, B and T cell production affected. Enzyme assay of RBC/WBC. Treatment by bone marrow/stem cell transplantation or enzyme replacement.

• Purine nucleotide phosphorylase – (Immunodeficiency) lymphopenia, thymic deficiency, recurrent infections, and hypouricemia, developmental delay, ataxia, or spasticity. T cell production affected. Enzyme assay of RBC, lymphocytes, fibroblasts. Treatment by bone marrow/stem cell transplantation.

• Adenine phosphoribosyl transferase – frequent infections, renal colic, renal failure. Elevated urine levels of 2,8-dihydroxyadenine, 8-hyroxyadenine, and adenine; serum uric acid normal. Enzyme assay. Treated with dietary purine restriction, high fluid intake, and avoidance of urine alkalinization, Allopurinol to prevent oxidation of adenine.

Pathway Disorders

X-linked recessive disorder• Hypoxanthine-guanine phosphoribosyl transferase –

(Lesch-Nyhan syndrome) usually presents at 3 to 12 months with orange sandy urine precipitate, dystonia, intellectual disability, self-mutilation (lips, tongue, fingers), and gout. Elevated serum and urine uric acid levels. Enzyme assay on RBC, lymphocytes, fibroblasts. Molecular genetics of gene. Treated supportively with low-purine diet, allopurinol, and plenty of hydration.

Glycogen Storage Disorders

hPPGSDVI

hG6PaseGSDI

mPPGSDV

debranching enzymeGSDIII

PFK-1GSDVII

transglycosylasebranching enzyme

GSDIV

GSGSD0

Glycogen

G1P

G6PGlc

UDP-Glc

F6P

F16BP

acid maltaseGSDII

ls

Pathway Disorders

Rare autosomal recessive disorders• Glycogen synthase –.(GSD type 0) fasting hypoglycemia,

ketosis, especially before feeding. Periodic acid-Schiff stain shows decreased hepatic glycogen stores, muscle is normal. Treatment is appropriate diet to avoid hypoglycemia.

• Glucose-6-phosphatase – (GSD type Ia, Von Gierke) history hypoglycemic seizures, hypotonia, hepatomegaly, xanthomas, manifestations of gout, hypertension, renal failure, and short stature. Fasting glucose, ischemic forearm test (negative), Enzyme assay. Treatment by high-protein diet, uncooked corn starch.

• Lysosomal acid maltase – (GSD type II, Pompe, a-1,4-glucosidase); infantile - feeding and breathing difficulties, hypotonia, cardiomegaly; adult – limb-girdle weakness, respiratory muscle involvement. Hyperlipidemia, fasting ketonemia. Ischemic forearm test normal. Enzyme assay of fibroblasts. Periodic acid-Schiff stain is positive for lysosomal glycogen inclusions. Treatment by enzyme relacement, high protein diet.

• Debranching enzyme – (GSD type III, Forbes-Cori, amylo-1,6-glucosidase), infantile seizures, hepatomegaly, growth retardation, progressive muscle weakness. Ischemic forearm test positive. Enzyme assay of fibroblasts. Periodic acid-Schiff stain is positive for basophilic glycogen deposits in all tissues. Treatment is supportive by corn starch, liver transplantation.

Pathway DisordersRare autosomal recessive disorders• Branching enzyme – (GSD type IV, Andersen,

transglucosidase) history not specific, hepatic failure, cirrhosis, hepatosplenomegaly, failure to thrive. Prenatal PCR and DNA analysis. Enzyme assay. Diffuse amylopectin-like deposits in the heart, liver, muscle, spinal cord, and peripheral nerves. Treatment is supportive with liver transplantation and diet.

• Myophosphorylase – (GSD type V, McArdle) cramps, fatigue, and pain after exercise (depends on severity of deficiency), unique "second-wind" phenomenon. Ischemic forearm test positive. Enzyme assay. Periodic acid-Schiff stain gives subsarcolemmal blebs. Treatment by avoiding intense exercise, provide high protein diet.

• Hepatic phosphorylase – (GSD type VI, Hers) most common among Mennonite religious group, also X-linked form, history of bulging abdomen, growth retardation, and slight delay in motor milestones, hepatomegaly. Enzyme assay on liver biopsy, RBC, WBC; molecular genetics of gene. Glycogen-distended hepatocytes, muscle normal. Treatment with dietary management as appropriate for clinical presentation.

• Phosphofructokinase-1 – (GSD type VII, Tarui, M form, classic) history of exertional fatigue, nausea and vomiting, muscle cramps, hyperuricemia, myoglobinuria following high-intensity exercise. Ischemic forearm test positive. Enzyme assay on muscle biopsy. Periodic acid-Schiff diastase-negative stain gives subsarcolemmal blebs. Treatment to avoid high carbohydrate diet especially before exercise.

Lysosomal Storage Disorders

Lipid metabolism• Landing, Sandhoff, Tay-Sachs, Krabbe,

Gaucher, Niemann Pick (A,B), Wolman, metachromatic leukodystrophy, Fabry

Glycoprotein metabolism• Schindler

Mucopolysaccharide metabolism• Hurler/Scheie, Hunter, Sanfilippo (A,B,C,D),

Morquio (A,B), Maroteaux–Lamy, Sly

Other lysosomal enzymes• Pompe, Niemann-Pick (C)

Oligosaccharidoses

NANA Gal GlcNAcMan

Man

NANA Gal GlcNAc

NANA Gal GlcNAc

NANA Gal GlcNAcMan GlcNAc

GlcNAc GlcNAc

Fuc

Asn12

3

456

7

8

a

a

a

a

a

a

b

b

b

b

bb b b3

4

4

4

5

5

56

6

6

Typical Asn-GlcNAc OS structure

Aspartylglycosylaminuria

4-L-Aspartylglycosylamine amidohydrolase

a-Mannosidosisa-MannosidaseGM2 gangliosidosis variant O

(Sandhoff-Jatzkewitz disease)b-N-Acetylhexosaminidases A&B

GM1 gangliosidosisb-Galactosidase

Mucolipidosis I (Sialidosis)

Sialidase

b-Mannosidosis

b-Mannosidase

Fucosidosisa-Fucosidase

Glycosaminoglycoses(mucopolysaccharidoses)

HS IdUA GlcN GlcUA GlcNAc

OSO3H OSO3H OSO3H

DS IdUA GalNAc GlcUA GalNAc

OSO3H OSO3H OSO3H

a aa

a

b

b b b

1

2

3

5

5

6

7,9

8

9

1

2 4

KS Gal GlcNAc Gal GlcNAc

OSO3H OSO3H OSO3H

b b b10

11

8

4

b

Aldurazyme®(laronidase)

Maroteaux-Lamy

N-acetylgalactosamine sulfatase

Sandhoff/Tay-Sachs

b-hexosaminidase A,B,S

Hunter’siduronate sulfatase

Hurler-Scheie

a-L-iduronidase

Mucolipodosis VII

b-glucuronidaseSanfilippo’s A

heparan N-sulfatase

Sanfilippo’s C

Acetyl-CoA: a-glucosaminide acetyltransferase

Sanfilippo’s D

N-acetylglucosamine-6-sulfatase

Sanfilippo’s BN-acetylglucosaminidase

Morquio’s A

N-acetylgalactose-6-sulfatase

Morquio’s B

-b galactosidase

Gangliosidoses

Cer PC

S + FA

Cer

neuraminidase(sialidase)

GD1Cer GalGlu

NANA

NANA

GalNAc Galbbbb

GM1Cer GalGlu

NANA

GalNAc Galbbbb

GM2Cer GalGlu

NANA

GalNAcbbb

GM3Cer GalGlu

NANA

bb

Cer GalGlubb

Cer Glub

Cer Gal GalGluabb

Cer Galb

Cer Gal SO3Hb

Cer Gal GalGlu GalNAcabb b

Generalized gangliosidosisb-galactosidase

Tay-Sachs diseaseb-hexosaminidase A

GM2 activator

Sialidosisneuraminidase

(sialidase)SAP-B

b-galactosidaseSAP-B, SAP-C

Gaucher’s diseaseb-glucosylceramidase

SAP-C

Sandhoff’s diseaseb-hexosaminidase A&B

Fabry’s diseasea-galactosidase A

SAP-B

Niemann-Pick diseasesphingomyelinase

Metachromatic leukodystrophyarylsulfatase A

SAP-B

Krabbe’s diseaseb-galactosylceramidase

SAP-A, SAP-CCerezyme

General Physical Features

• Coarse facial features (sometimes with macroglossia)

• Corneal clouding or related ocular abnormalities

• Angiokeratoma• Umbilical/inguinal hernias• Short stature• Developmental delays• Joint or skeletal deformities• Organomegaly (especially liver and

spleen)• Muscle weakness or lack of control

(ataxia, seizures, etc.)• Neurologic failure/decline or loss of gained

development

mit

Heme Synthesis

SCoA + Gly

5AS

5ALAPBGPBGS

PBGD

HMB

UPGIIIS

UPGIII

UPGIIIDC

CPGIIICPGO

PPGIX

PPIX

PPGO

FC

Heme

Pathway Disorders• PBG synthase – (5-aminolevulinic acid dehydratase) extremely

rare autosomal recessive (hepatic porphyria) neurological findings, abdominal tenderness, neuropathy, not associated with cutaneous photosensitivity. Elevated urine ALA, coproporphyrin III and protoporphyrin IX, normal PBG, elevated RBC zinc protoporphyrin but decreased (80%) PBG synthase. DNA analysis. Treatment by avoiding precipitating factors, drugs that induce P450 induction, provide hematin, high carbohydrate diet (glucose inhibits 5-AS).

• PBG deaminase – (Acute intermittent porphyria) autosomal dominant, abdomen pain, psychiatric symptoms (hysteria), motor neuropathies (more commonly lower limbs), and constipation but no skin rash. Increased urinary porphobilinogen secretion, molecular genetic analysis. Treatment during attacks with high carbohydrate (glucose) diet and hematin, otherwise, balanced diet.

• Uroporphyrinogen III synthase – (Congenital erythropoetic porphyria, Gunther disease) rare autosomal recessive, photosensitivity, nail abnormalities, brown or pink teeth. Elevated urine and RBC levels of uroporphyrin I, hemolytic anemia. Enzyme assay, molecular genetic analysis, red porphyrin fluorescence in intact RBC and erythroid precursor cells. Treated with absolute avoidance of sun exposure, supportive/cosmetic care.

• Uroporphyrinogen III decarboxylase – (Porphia cutana tarda) 80% acquired/20% familial/autosomal dominant, acquired by ethanol abuse, estrogen therapies, hemochromatosis genes, hepatitis and human immunodeficiency viral infections, environmental toxins, photosensitivity, tea/wine colored urine. Carboxylated porphyrins in serum and urine. Enzyme assay of RBC, molecular genetic analysis. Treatment with avoidance of sunlight/environmental exposure.

Pathway Disorders

• Coproporphyrinogen oxidase – (Hereditary coproporphyria) autosomal dominant, abdominal pain, neuropathies (motor, lower limbs), constipation, and skin changes (photosensitivity). Excess secretion and levels of coproporphyrins in stool and urine. Treatment with high carbohydrate (glucose) diet and hematin.

• Protoporphyrinogen oxidase – (Variegate porphyria) autosomal dominant, photosensitivity, abdominal discomfort. Urinary aminolevulinic acid and porphobilinogen levels are greatly elevated during attacks, molecular genetic analysis. Treatment with avoidance of inducing drugs, providing high carbohydrate diet, hematin.

• Ferrochelatase – (Erythropoetic protoporphyria) autosomal dominant (X-linked, autosomal recessive), photosensitivity, heptabiliary disease, jaundice. Elevated protoporphyrin concentration in red blood cells, plasma, bile, and feces. Treatment with avoidance of sun exposure, maintain balanced diet.

Heme Degradation

BVRBR

indirectunconjugatedpre-hepatic

HOBVHeme

ER

hepatocyte

directconjugatedpost-hepatic

albumin

albumin-BR

ligandin

albumin

ligandin-BR

BR diglucuronide

UDP-GT

res

Pathway Disorders

Autosomal recessive disorders• UDP-glucuronyl transferase – mild deficiency (Gilbert

syndrome) most common inherited cause of unconjugated hyperbilirubinemia, intermittent jaundice without hemolysis or liver disease, precipitated by dehydration, fasting, menstrual periods, intercurrent illness, trauma, over exertion, nonspecific symptoms such as abdominal cramps, fatigue, and malaise, mild jaundice. Unconjugated hyperbilirubinemia (by definition [bilirubin] < 6 mg/dL, commonly < 3 mg/dL), normal complete blood count, reticulocyte count, and blood smear, normal liver function panel. Treatment is reassurance and avoiding precipitating factors.

• UDP-glucuronyl transferase – severe deficiency (Crigler-Najjar syndrome) rare, types 1 and 2 (Arias syndrome). Type 1 almost complete deficiency associated with neonatal unconjugated hyperbilirubinemia (17-50 mg/dL) and kernicterus, hypotonia, deafness, oculomotor palsy, lethargy. Type 2 deficiency unconjugated bilirubin (6-20 mg/dL), persistent jaundice at birth or after. Elevated unconjugated bilirubin with normal liver function panel. Phenobarbital treatment distiguished type 1 (no effect) from type 2 (lowers serum bilirubin 25%). Treatment of bilirubin encephalopathy with plasma exchange transfusion and long-term phototherapy.

Integration of Metabolism

SSB• metabolism in brain, nervous tissue and muscle• alcohol processing and effect on metabolic pathways• vitamins in neuromuscular metabolism

ERG• regulation of metabolism and diabetes