Further analysis was performed by IEM panel, and 2 of the lost to follow-up subgroup were identified biallelic mutations in CPS1 and ACADSB gene in two subjects with clinical diagnosis of carbamoyl phosphate synthetase I deficiency and 2-methylbutyryl-CoA dehydrogenase deficiency respectively (Additional file 1: Table S4). The gene discussed is ACADSB; the disease is hyperinsulinemic hypoglycemia, familial, 4.