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A newborn becomes lethargic with metabolic acidosis, hyperammonemia, and ketosis. Urine organic acids show markedly elevated methylmalonic acid.
AR
- MUT (methylmalonyl-CoA mutase): mut0 or mut-
- MMAA, MMAB (B12 metabolism): some B12-responsive
- Metabolic acidosis with high anion gap
- Hyperammonemia, hypoglycemia, ketosis
- Neutropenia, thrombocytopenia
- Long-term: renal failure, basal ganglia injury
- On RUSP
- Detected on newborn screening: elevated C3 (propionylcarnitine), often with elevated C3/C2 ratio
- Urine organic acids: markedly elevated methylmalonic acid (with methylcitrate); plasma homocysteine distinguishes combined cobalamin defects
- Confirmation: molecular testing (MUT, MMAA, MMAB); cobalamin-responsiveness assessed by B12 trial
- Protein restriction, B12 (cobalamin) trial, carnitine, liver/kidney transplant
"Micturition in Methylmalonic": MMA patients develop renal failure (kidney = "micturition" = peeing). Contrast with propionic acidemia, where patients develop issues with the Pump (cardiac disease).
NBS: High C3 (propionylcarnitine): elevated C3 on newborn screening acylcarnitine profile (same marker as propionic acidemia).
VoMIT amino acids: Valine, Methionine, Isoleucine, Threonine are the precursors that feed into the propionyl-CoA/methylmalonyl-CoA pathway. Restrict these in the diet.