Methylmalonic acidemia: Current status and research priorities

Methylmalonic acidemia (MMA) is a lethal, severe heterogeneous disorder of methylmalonate and cobalamin (cbl; vitamin B12) metabolism with poor prognosis. Two main forms of the disease have been identified, isolated methylmalonic acidurias and combined methylmalonic aciduria and homocystinuria, which is respectively caused by different gene mutations. Here, we review the improvement of pathogenesis, diagnosis and treatment in MMA. Importantly, the reported epidemiological data of MMA patients in China and the hot mutation sites in Chinese patients are listed, which will aid in improving healthcare of Chinese patients in the future. c.729_730insTT was the most common mutation in Chinese isolated MMA patients, while c.609G>A and c.658_660delAAG were in Chinese cblC type patients according to unrelated studies. The estimated newborn screening incidence was reported to be 1:26,000, 1:3,920, 1:11,160, 1:6,032 respectively in Beijing and Shanghai, Shandong province, Taian district, and Henan province of China. Alternatively, when patients with suspected inherited metabolic diseases were used as the screened sample, the relatively high incidence 0.3% and 1.32% were respectively obtained in southern China and throughout all the provinces of mainland China and Macao with the exception of five provinces (Hainan, Neimenggu, Tibet, Ningxia, and Hong Kong).