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
Ornithine transcarbamylase (OTC) deficiency X-linked recessive
Defect / target: Ornithine transcarbamylase (mitochondrial urea cycle enzyme, carbamoyl phosphate + ornithine → citrulline)
Mechanism: Carbamoyl phosphate made by CPS-I cannot combine with ornithine, backs up, leaks to the cytosol and feeds aspartate transcarbamylase in pyrimidine synthesis, overproducing orotic acid while ammonia accumulates.
↑ Accumulates: Ammonia, carbamoyl phosphate, orotic acid (orotic aciduria)· ↓ Deficient: Citrulline (low), urea
Presentation: Most common urea cycle disorder; full-term newborn normal at birth (maternal clearance in utero), then at 24–48 h lethargy, refusal to feed, tachypnea, seizures, vomiting → coma
Labs: Elevated serum ammonia AND elevated urinary orotic acid (distinguishes from hereditary orotic aciduria, where ammonia is normal); low BUN
Treatment: Protein restriction + nitrogen-scavenger drugs (phenylbutyrate, benzoate) that bypass the enzyme
Orotic aciduria WITH hyperammonemia = OTC; X-linked is 'unique' among UCDs; citrulline is your compass
Learn the mechanism: Pyrimidine synthesis (& thymidylate) →
FMK 07.1 Amino Acid Metabolism I; FMK 08.1 Nucleic Acid Metabolism · slide 07.1: 2, 15, 18, 19, 32; 08.1: 23, 26, 28, 29