Objective: To investigate the clinical manifestations, biochemical abnormalities and pathogenic variants among children with Short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency detected by neonatal screening.
Methods: A total of 2 730 852 newborns were screened from January 2016 to December 2021 with liquid chromatography tandem mass spectrometry. Suspected SBCAD deficiency patients were diagnosed by urine organic acid analysis and high-throughput gene sequencing analysis. The clinical, biochemical and genetic changes of the confirmed cases were analyzed, in addition with guidance for diet and life management, L-carnitine supplement, and survey of growth and intellectual development.
Results: Twelve cases of SBCAD deficiency were diagnosed, which yielded a prevalence of 1/227 571. The lsovaleryl carnitine (C5) of primary screening blood samples was between 0.6 and 2.1 µmol/L, all exceeded the normal range. C5/acety1 carnitine (C2) was between 0.02 and 0.12, with 6 cases exceeding the normal range. C5/propionyl carnitine (C3) was between 0.1 and 1.16, with 5 cases exceeding the normal range. Free carnitine (C0) was between 18.89 and 58.12 µmol, with 1 case exceeding the normal range. Three neonates with abnormal screening results were recommended to have appropriate restriction for protein intake and two were given L-carnitine. During follow-up, their C5 has ranged from 0.22 to 2.32 µmol/L, C5/C2 has ranged from 0.01 to 0.31, C5/C3 has ranged from 0.14 to 1.7. C5 or C5/C2 and C5/C3 were transiently normal in all patients except for case 8 during the neonatal screening and follow-up. C0 was 17.42 ∼ 76.83 µmol/L Urine organic acid analysis was carried out in 9 of the 12 cases, and 2-methylbutyroglycine was elevated in 8 cases. Urine organic acid analysis was carried out in 9 cases, and 2-methylbutyrylglycine was increased in 8 cases. Genetic analysis was carried out for 11 children, and in total 6 ACADSB gene variants were identified, which included 4 missense variants (c.655G>A, c.923G>A, c.461G>A, c.1165A>G), 1 frameshift variant (c.746del) and 1 nonsense variant (c.275C>G). Among these, the C.461G>A variant was unreported previously. The most common variants were c.1165A>G (40.9%) and C.275C>G (22.7%). The patients were followed up for 18 days to 55 months. Only one patient had mental retardation, with the remainders having normal physical and mental development.
Conclusion: SBCAD deficiency is a rare disease. The detection rate of newborn screening in this study was 1/227 571. Early intervention can be attained in most asymptomatic patients through neonatal screening. In this study, the common gene variants are c.1165A>G and c.275C>G.