Objective: Methylmalonic acidemia (MMA) is one of the most common disorders of congenital organic acid metabolism. This study aimed at exploring the clinical characteristics and treatment of the disease to help improve our understanding of it.
Methods: The clinical data of 14 patients with MMA admitted to our hospital between January 2002 and July 2003 were analyzed and the diagnoses were confirmed by gas chromatography/mass spectrometry (GC/MS). The patients consisted of 4 males and 10 females, whose age of onset ranged from birth to 9 years with 7 cases younger than 1 month (50%) and 10 cases younger than 1 year (71%).
Results: The main clinical manifestations were lethargy (6 cases), developmental retardation or regradation (7 cases), convulsion (6 cases), recurrent vomiting (4 cases), difficulty with feeding (4 cases), muscular dystonia (5 cases with hypotonia, 3 with hypertonia) and yellowish hair (4 cases), etc. Some cases were also presented with hair loss, hepatomegaly, ataxic or stiff gait, and motor weakness with muscular atrophy. The laboratory findings showed metabolic acidosis in 6 cases, hyperammonemia in 5 cases, ketonuria in 4 cases and remarkable elevation of urinary methylmalonic acid concentration in all cases. Some abnormalities in globus pallidus and cerebral white matter as well as diffuse cerebral atrophy were noted by the brain CT and MRI in 5 respective cases, while 4 cases did not receive neuroradiological examinations. Peripheral neuropathies were found by electromyography in 2 patients and bilateral optic nerve atrophy was detected by eyeground examination in 1 child. Three patients died before the diagnoses were made. Of the 11 survivals, 10 children have received therapy of vitamin B12 (VitB12) and supplementation of L-carnitine with restricted-protein diet. The follow-up for a period ranging from 3 months to 1.5 year (mean 8.5 months) of 7 cases with medical therapy showed a favorable outcome without any symptoms in 1 case and apparent improvement in 4 cases (the diffuse cerebral atrophy in MRI completely recovered in one case), however, 2 patients died from severe metabolic acidosis.
Conclusions: The main clinical features of MMA include lethargy, developmental retardation or regradation, convulsion, recurrent vomiting, difficulty with feeding, muscular dystonia, yellowish hair, metabolic acidosis, hyperammonemia and ketonuria, etc. Urine organic acids analysis with GC/MS is critical to the early diagnosis of MMA. Early diagnosis and appropriate long-term treatment are essential to improve the prognosis of the disease.