Inborn errors of metabolism detectable by tandem mass spectrometry in Beijing

Background Individual inborn errors of metabolism (IEMs) are rare disorders. Expanded newborn screening for IEMs by tandem mass spectrometry (TMS) is an efficient approach for early diagnosis. Here we provide the newborn screening program for the application of this approach (between July 2014 and March 2019) to the identification of newborns in Beijing at risk of developing a potentially fatal disease. Methods The amino acids and acylcarnitines in dried blood spots were analyzed by TMS. Diagnoses of newborns with elevated metabolites were confirmed by gas chromatography-mass spectrometry, biochemical studies, and genetic analysis. Results Among the healthy newborns, 16 metabolic disorder cases were confirmed, giving a total birth prevalence of 1:3666 live births. Organic acidemia (OA) was the most common (9/16 patients; 56%), and methylmalonic acidemia was the most frequently observed OA (7/9 patients; 89%). Five infants were diagnosed with methylmalonic acidemia with homocystinuria type CblC, two with isolated methylmalonic acidemia, one with propionic acidemia, and one with isovaleric acidemia. Four patients (4/16, 25%) were diagnosed with hyperphenylalaninemia. One suffered with medium-chain acyl CoA dehydrogenase deficiency, one with carnitine uptake deficiency, and one with citrin deficiency. Eleven cases underwent genetic analysis. Seventeen mutations in eight IEM-associated genes were identified in 11 confirmed cases. Symptoms were already present within 2 days after birth in 44% (7/16) cases. The infant with propionic acidemia died at 7 days after birth. The other cases received timely diagnosis and treatment, and most of them grew well. Conclusions The results illustrate challenges encountered in disease management highlighting the importance of newborn screening for inherited metabolic disorders, which is not yet nationally available in our country. Regional newborn screening programs will provide a better estimation of the incidence of IEM.