Learn / FMK
Every FMK condition
299 diseases, deficiencies, toxicities and drug mechanisms harvested from every FMK deck — the ones sprinkled through a single bullet as much as the ones with their own slide. Pick what you're given and what you have to name, or let it cycle; distractors come from the same category so you have to discriminate (hypoketotic vs. ketotic hypoglycemia, which GSD, which urea-cycle enzyme…). Every answer shows the whole card with the lecture and slide.
Amino acid · FMK 07.1
Cystathioninuria Autosomal recessive
Defect / target: Cystathioninase (cystathionine γ-lyase, downstream of CBS; B6-dependent)
Mechanism: Cystathionine cannot be hydrolyzed to cysteine + α-ketobutyrate, so it accumulates and spills into urine.
↑ Accumulates: Cystathionine (urine)· ↓ Deficient: Cysteine (mild)
Presentation: Generally benign — often an incidental finding
Labs: Cystathionine in urine
Cystathioninuria = enzyme defect, benign
Learn the mechanism: Methionine cycle & homocysteine's two fates →
FMK 07.1 Amino Acid Metabolism I · slide 28, 31, 32