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.
Carbohydrate · FMK 03.4
Hereditary fructose intolerance (HFI) Autosomal recessive
Defect / target: Aldolase B (fructose-1-phosphate aldolase) deficiency
Mechanism: Fructokinase still traps fructose as fructose-1-phosphate, but aldolase B cannot cleave it. F1P accumulates, sequestering inorganic phosphate and depleting ATP; the falling ATP blocks gluconeogenesis and glycogenolysis (hypoglycemia) and the AMP that builds up is degraded to uric acid (secondary hyperuricemia).
↑ Accumulates: Fructose-1-phosphate, uric acid· ↓ Deficient: Intracellular phosphate and ATP
Presentation: Well until fructose/sucrose/sorbitol enters the diet — classically at weaning onto fruit or sweetened food. Vomiting, hypoglycemia, hepatomegaly, jaundice and failure to thrive after feeds; children develop a strong aversion to sweets and are strikingly caries-free. Untreated it causes liver and renal tubular damage.
Labs: Reducing sugar positive in urine but glucose oxidase dipstick negative (fructose is a reducing sugar the dipstick misses); hypoglycemia after a fructose load, elevated LFTs, hyperuricemia. Confirm by ALDOB gene testing — the fructose tolerance test is dangerous and no longer used.
Treatment: Lifelong exclusion of fructose, sucrose and sorbitol (check medications and IV fluids); treat acute hypoglycemia with glucose
Contrast with essential fructosuria: fructoKINASE deficiency is benign because fructose is never trapped, whereas HFI traps it as F1P and does the damage. 08.1 revisits HFI beside von Gierke as an 'unrelated metabolic disease with secondary purine overproduction'.
Learn the mechanism: Fructose metabolism →Reasoning case →
FMK 03.4 Fructose, Galactose & Ethanol Metabolism · slide 03.4: 6, 8, 23, 24, 25, 26; 08.1: 19 · also mentioned in FMK 08.1 Nucleic Acid Metabolism