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Biochemistry — Metabolic Maps — USMLE Step 2 CK Notes
Free, high-yield revision notes for USMLE Step 2 CK. Read here, or drill the same material as questions and flashcards in the app.
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Enzyme-deficiency diseases the exam returns to
- Von Gierke (I): glucose-6-phosphatase → severe fasting hypoglycaemia, lactic acidosis, hepatomegaly
- Pompe (II): lysosomal acid alpha-glucosidase → cardiomegaly, hypotonia
- McArdle (V): myophosphorylase → exercise intolerance, no lactate rise on exertion
- Classic galactosemia: GALT → cataracts, jaundice, hepatomegaly with lactose feeding
- PKU: phenylalanine hydroxylase → musty odour, intellectual disability; restrict phenylalanine
Urea cycle
- OTC deficiency: X-linked, high ammonia, high orotic acid, low BUN
- Orotic acid HIGH + ammonia HIGH → OTC; orotic acid high + ammonia NORMAL → hereditary orotic aciduria
Vitamins as cofactors
- B1 (thiamine): pyruvate dehydrogenase, transketolase → Wernicke; give before glucose
- B6 (pyridoxine): transaminases, neurotransmitters → depleted by isoniazid
- B12 and folate: methylation and DNA synthesis → megaloblastic anaemia
- B12 uniquely also causes subacute combined degeneration; folate does not
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