3-Methylcrotonyl-CoA carboxylase deficiency newborn screening in a population of 536,008: is routine screening necessary?

Objective: To evaluate whether 3-methylcrotonyl-CoA carboxylase deficiency (3-MCCD) should be routinely screened in newborns. Methods: Dried blood spots (DBS) were collected and analyzed by tandem mass spectrometry (TMS). Blood samples were collected from infants with positive 3-MCCD results. Targeted sequencing was performed using the extended panel for inherited metabolic diseases to detect 306 genes. The sequencing libraries were quantified and used for massively parallel sequencing on the Illumina HiSeq 2500 platform. Results: A total of 536,008 infants underwent newborn screening (NBS) and 14 cases of 3-MCCD were diagnosed. The incidence of 3-MCCD in Jiangsu province was 1:38,286. During the last 3 years of follow-up, none of the subjects with 3-MCCD exhibited obvious clinical symptoms. Only two children had mild feeding difficulties and vomiting. Eleven patients had complex variants of the MCCC1 gene, and three patients had mutations in MCCC2. In total, 17 types of MCCC1 or MCCC2 variants were found, and c.639 + 2t > a was the most common mutation. Conclusions: As far as the current results are concerned, 3-MCCD may be benign in Jiangsu province. However, additional investigations and a longer follow-up period are necessary to decide whether NBS of 3-MCCD is necessary or not.