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 07.2
BH₄-deficient hyperphenylalaninemia (dihydropteridine reductase / DHPR deficiency, variant PKU) Autosomal recessive
Defect / target: Dihydropteridine reductase (DHPR), which regenerates tetrahydrobiopterin (BH₄) from BH₂
Mechanism: BH₄ cannot be recycled, starving phenylalanine hydroxylase AND tyrosine hydroxylase AND tryptophan hydroxylase, so dopamine/norepinephrine/epinephrine and serotonin synthesis fail even when dietary Phe control normalizes phenylalanine.
↑ Accumulates: Phenylalanine (unless diet-restricted); BH₂· ↓ Deficient: BH₄; dopamine, norepinephrine, epinephrine, serotonin
Presentation: Infant on a perfect low-Phe diet with normal Phe still develops truncal hypotonia, stiff limbs, movement disorder, difficulty swallowing, seizures — progressive neurologic decline despite biochemical improvement
Labs: Phe falls on diet yet neurologic symptoms progress
Treatment: Poor response to low-Phe diet alone
One cofactor, three hydroxylases: diet controls one, this defect silences three
Learn the mechanism: Catecholamines, serotonin & the tyrosine tree →
FMK 07.2 Amino Acid Metabolism II · slide 07.2: 2, 6, 8, 12, 27; 07.1: 25, 26