USMLE step 1 – biochemistry Exam Questions & Answers 2023/2024

USMLE step 1 – biochemistry Exam Questions & Answers 2023/2024 infant with somnolence, vomiting, cerebral edema, decreased BUN, hyperammonemia - ANSWER-ornithine transcarbamoylase deficiency infantile cataracts, doesn't track objects, absent social smile - ANSWER-galactokinase deficiency infantile cataracts, hepatomegaly, jaundice, failure to thrive - ANSWER-uridyltransferase deficiency causes of Down syndrome - ANSWER-1) meiotic nondisjunction (95%) 2) unbalanced robertsonian translocation (extra arm on Ch 21) 3) mosaic trisomy 21 treatment of hyperammonemia (HCV, urea cycle deficiency) - ANSWER-limit protein in diet benzoate, phenylbutarate (bind a.a.'s, increased aa exretion) actulose (acidify GI tract, trap NH4 for excretion) effect of hyperammonemia on metabolism - ANSWER-decreased alpha ketoglutarate, inhibiting TCA cycle Tay-Sach's (enzyme, accumulated substance) - ANSWER-hexosaminidase, GM2 ganglioside metachromatic leukodystrophy (enzyme, accumulated substance) - ANSWER-arylsulfatase, cerebroside sulfate fabry's (enzyme, accumulated substance) - ANSWER-alpha-galactosidase, ceramide trihexoside