We have initiated clinical selective screening for inborn errors of metabolism in China by analysing amino acids and acylcarnitines in a dried blood filter-paper samples using tandem mass spectrometry. Samples from a total of 3070 children suspected of inborn errors of metabolism were collected through a study network which covered most provinces of China. The diagnoses were further confirmed through clinical symptoms, by gas chromatography-mass spectrometry and other biochemistry studies, and in a few cases by DNA analysis. In all, 212 cases were diagnosed (6.6%) including 92 (43.4%) with amino acids disorders (48 with phenylketonuria, 12 with ornithine carbamoyltransferase deficiency, 7 with tyrosinaemia type I, 9 with maple syrup urine disease, 5 with citrullinaemia type I, 8 with citrullinaemia type II, 2 with homocystinuria, and 1 with argininaemia); 107 (50.5%) with organic acid disorders (including 58 with methylmalonic acidaemia, 13 with propionic acidaemia, 6 with isovaleric acidaemia, 7 with glutaric acidaemia type I, 6 with 3-methylcrotonyl-CoA carboxylase deficiency, 2 with 3-hydroxy-3-methylglutaryl-CoA lyase deficiency, 10 with multiple carboxylase deficiency, and 5 with beta-ketothiolase deficiency); and 13 (6.1%) with fatty acid oxidation disorders (including 1 with carnitine palmitoyltransferase deficiency type I, 1 with carnitine palmitoyltransferase deficiency type II, 1 with short-chain acyl-CoA dehydrogenase deficiency, 5 with medium-chain acyl-CoA dehydrogenase deficiency, 3 with very long-chain acyl-CoA dehydrogenase deficiency, and 2 with multiple acyl-CoA dehydrogenase deficiency). It is suggested that tandem mass spectrometry is useful for selective screening of clinically suspected patients. The majority of diseases (94%) in this study were amino acid disorders and organic acid disorders. Fatty acid oxidation disorders are relatively rare in the Chinese, but medium-chain acyl-CoA dehydrogenase deficiency should be further investigated.

Early recognition of biotinidase deficiency is crucial to avoid permanent damage. Determination of biotinidase activity should be included in neonatal screening in China. Exon 4 may be a hot-spot for biotinidase gene mutations in Chinese patients. Four novel gene variations may be disease-causing mutations and should be confirmed by expression studies.

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