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Reference Tables

1. Glycogen Storage Diseases (AR)

Mnemonic: Very Poor Carbohydrate Metabolism (Types I, II, III, V)

Type/Name	Enzyme	Key Findings
I: Von Gierke	Glucose-6-phosphatase	Severe fasting hypoglycemia, ↑ Lactate, ↑ Uric acid (Gout), Hepatomegaly. Tx: Cornstarch.
II: Pompe	Lysosomal α-1,4-glucosidase	"Pompe trashes the Pump" (Cardiomegaly), hypotonia. No hypoglycemia.
III: Cori	Debranching enzyme	Milder Type I. Normal blood lactate. Gluconeogenesis intact.
V: McArdle	Muscle glycogen phosphorylase	Muscle cramps, Myoglobinuria (red urine) with exercise. Flat venous lactate.

2. Lysosomal Storage Diseases

Disease	Enzyme	Accumulates	Key Findings
Tay-Sachs	Hexosaminidase A	GM2 ganglioside	Cherry-red spot, No hepatosplenomegaly, Onion skin lysosomes.
Fabry (XR)	α-galactosidase A	Ceramide trihexoside	Neuropathy, Angiokeratomas, Hypohidrosis. Late: Renal failure.
Metachromatic	Arylsulfatase A	Cerebroside sulfate	Demyelination, Ataxia, Dementia.
Krabbe	Galactocerebrosidase	Galactocerebroside	Globoid cells, Oligodendrocyte destruction, Optic atrophy.
Gaucher	Glucocerebrosidase	Glucocerebroside	Hepatosplenomegaly, Bone crises, Gaucher cells (tissue paper).
Niemann-Pick	Sphingomyelinase	Sphingomyelin	Hepatosplenomegaly, Cherry-red spot, Foam cells.
Hurler (MPS I)	α-L-iduronidase	Heparan/Dermatan	Gargoylism, Corneal clouding, Airway obstruction.
Hunter (MPS II)	Iduronate-2-sulfatase	Heparan/Dermatan	Mild Hurler + Aggression, No corneal clouding. (XR)

3. Amino Acid Disorders

Disease	Enzyme/Defect	Key Notes
PKU	Phenylalanine hydroxylase	Musty odor, Intellectual disability, Eczema. Can also be BH4 (Tetrahydrobiopterin) deficiency.
MSUD	Branched-chain α-ketoacid Dehydrogenase	Maple syrup urine odor. Blocks Ile, Leu, Val.
Alkaptonuria	Homogentisate oxidase	Ochronosis (black connective tissue), Black urine on standing.
Homocystinuria	Cystathionine synthase	Marfanoid habitus, Downward lens subluxation, Thrombosis.
Cystinuria	PCT Transporter (COLA)	Hexagonal stones. Poor reabsorption of Cystine, Ornithine, Lysine, Arginine.

4. Urea Cycle & Carbs

Disease	Defect	Key Notes
OTC Deficiency (XR)	Ornithine Transcarbamylase	↑ Orotic acid, ↓ BUN, Hyperammonemia. No megaloblastic anemia.
Classic Galactosemia	GALT (Uridyltransferase)	Cataracts, E. coli sepsis, Jaundice. Symptoms start with feeding.
Hereditary Fructose	Aldolase B	Hypoglycemia, Jaundice, Vomiting after fruit/juice.
Essential Fructosuria	Fructokinase	Benign, asymptomatic. Fructose in urine.

5. Lipids, Transport & Abbreviations

Abbrev	Full Name	Function / Disease Association
LPL	Lipoprotein Lipase	Degrades TG in circulating chylomicrons. Defect = Type I Hyperchylomicronemia.
LCAT	Lecithin-Cholesterol Acyltransferase	Esterifies cholesterol (nascent HDL -> mature HDL). Defect = Corneal arcus, hemolytic anemia.
CETP	Cholesteryl Ester Transfer Protein	Transfers cholesteryl esters from HDL to VLDL/LDL.
MTP	Microsomal Triglyceride Transfer Protein	Loads lipids onto ApoB-48/ApoB-100. Defect = Abetalipoproteinemia.
HMG-CoA	3-hydroxy-3-methylglutaryl-CoA	Rate-limiting enzyme for Cholesterol synthesis. Target of Statins.
ABCA1	ATP-binding cassette transporter A1	Cholesterol efflux pump. Defect = Tangier Disease (orange tonsils).
MCAD	Medium-Chain Acyl-CoA Dehydrogenase	Fatty acid oxidation enzyme. Defect = Hypoketotic hypoglycemia.

6. Porphyrias & Heme

Disease	Enzyme	Notes
AIP	Porphobilinogen (PBG) deaminase	Accumulates PBG & ALA. 5 P's (Pain, Psych, etc).
PCT	Uroporphyrinogen decarboxylase	Blistering photosensitivity. Tea-colored urine.
Lead Poisoning	ALA Dehydratase & Ferrochelatase	Basophilic stippling (ribosome aggregation).

7. Melanin & Others

Disease	Defect	Key Notes
Albinism	Tyrosinase	Normal melanocyte count, ↓ melanin production.
Chediak-Higashi	LYST (Traffic)	Giant granules, Partial albinism, Pyogenic infections.
Piebaldism	Migration	White forelock.
Lesch-Nyhan (XR)	HGPRT	Self-mutilation, Gout, Orange sand in diaper.
G6PD (XR)	G6PD	Heinz bodies, Bite cells. Hemolysis via oxidant stress.