Objective: To establish a specific procedure for the high-risk screening and diagnosis of organic acidurias and other inherited metabolic diseases in China.
Methods: A nation-wide network for the high-risk screening and diagnosis of genetic metabolic diseases was formed to facilitate the collaboration. Urine samples were collected using filter paper from patients with clinical symptoms suspicious of inherited metabolic diseases. The samples were eluted with distilled water and internal standards were added. Samples were treated with hydroxylamine hydrochloride to form oximes to improve the recoveries of 2-ketoacids. Urinary organic acids were extracted with ethyl acetate and diethyl ether under acidic condition. After dehydration, the combined organic phase was evaporated to dryness with nitrogen. The residues were added with BSTFA + 1%TMCS and heat incubated to form the trimethylsilyl derivatives, and then were analyzed on an Agilent 5890/5973N gas chromatography-mass spectrometer (GC-MS), with a 7683 series auto-sampler. The peaks were identified by reference to a mass spectral library.
Results: Totally 352 samples were collected from the network collaborating hospitals since 2001. Thirty-four (9.66%) cases of various inherited metabolic diseases were diagnosed with an age range of 2 days to 14 years. The disease profile was consisted of methylmalonic acidemias (6), alpha-keto-glutaric aciduria (5), tyrosinemia type I (4), dicarboxylic aciduria (4), multiple carboxylase deficiency (3), phenylketonuria (3), lactic acidemia (3), propionic acidemia (2), ornithine transcarbamoylase deficiency (1), ethylmalonic-adipic aciduria (1), glutaric aciduria type II (1) and 3-methylcrotyl CoA carboxylase deficiency (1). The most common clinical symptoms and signs included mental and developmental retardation, convulsion, musculotonic abnormality and jaundice. Routine laboratory tests often revealed metabolic acidosis, hypoglycemia and hyperammonemia, etc.
Conclusion: Urine organic acids analysis by GC-MS remains to be the most important technique for the high-risk screening and diagnosis of inherited metabolic diseases. Use of urine filter paper for sample collection and analysis in advanced genetic metabolic centers is a practical approach to extend the diagnostic capacity and improve the management of such diseases in China. Collaborative network played a critical role in the success of the program.