To explore the diagnostic features of mthylmalonic acidemia.

The clinical data of a 4-months-old infantile combined with methylmalonic acidemia and homocysteinemia who was diagnosed in the first People’s Hospital of Jining was retrospectively analyzed, the relevant literatures were reviewed.

The boy mainly presented with global developmental delay, drowsiness, feeding difficulties, binocular gaze and repeated skin rash.The ambulatory electroencephalogram (AEEG) was negative.The cerebral magnetic resonance imaging(MRI) showed cerebral hypoplasia.The neurological development was moderate mental retardation.The blood homocysteine was 117.60 μmol/L.The result of blood tandem mass spectrometry was abnormal, the concentrations of methionine and carnitine were 3.40 μmol/L and 4.96 μmol/L, respectively.The ratios of C3/C2 and C3/C0 were elevated.Urine organic acid analysis showed that the level of methylmalonic acid was elevated obviously which was 303.19 μmol/L, with elevated 3 hydroxy propionic acid and methyl citrate, which were 21.07 μmol/L and 5.43 μmol/L, respectively.The diagnosis was confirmed by molecular genetic study of the gene MMACHC, and there were two nonsense mutations (c.217C>T, p.R73X and c. 609G>A, p.W203X). The compound heterozygous mutations were from his parents respectively.He was diagnosed with cb1C-type methylmalonic acidemia and homocysteinemia.

The clinical features of methylmalonic acidemia are nonspecific.Diagnosis relies on analysis of organic acids in plasma and/or urine by gas-liquid chromatography and mass spectrometry.Establishing the specific subtype of methylmalonic acidemia requires molecular genetic testing.