Enzymes affected (a mitochondrial enzymes):
(1) methylmalonyl-CoA mutase (MCM)
(2) methylmalonyl-CoA epimerase (MCE)
(3) cobalamin A, cobalamin B, or cobalamin D, resulting in a deficiency of 5'-deoxyadenosylcobalamin
Genes affected:
(1) MUT
(2) MCEE
(3) MMAA, MMAB or MMADHC
Chemicals that accumulate: methylmalonic acid, methylmalonylcarnitine, propionyl-CoA, propionic acid, 3-hydroxypropionic acid, propionylcarnitine, propionylglycine or 2-methylcitrate
Onset: usually during early childhood due to a metabolic decompensation
Triggers for a metabolic decompensation:
(1) acute trauma
(2) infection or fever
(3) excessive exercise
(4) any physiologic stress
(5) fasting
(6) vomiting
(7) relatively high protein intake
(8) medication
An episode of metabolic decompensation may involve:
(1) vomiting
(2) anorexia
(3) dehydration
(4) lethargy
(5) hypotonia
(6) convulsions
(7) coma
(8) multi-organ failure
Clinical manifestations may include:
(1) hepatomegaly and/or hyperechoic liver
(2) cognitive deficits
(3) psychomotor retardation
(4) muscular hypotonia and/or movement disorders
(5) CNS lesions (white matter, basal ganglia)
(6) epilepsy
(7) joint hypermobility
(8) pes planus
(9) enamel defects in teeth
(10) renal failure
(11) stroke-like episodes
(12) growth retardation and short stature
Less common findings may include:
(1) cardiomyopathy
(2) pancreatitis
(3) optic atrophy
(4) sensorineural hearing loss
(5) acrodermatitis dysmetabolica
Laboratory findings during an acute exacerbation:
(1) metabolic acidosis
(2) lactic acidosis
(3) hyperammonemia
