Newborn Screening of Primary Carnitine Deficiency and Prenatal Genetic Diagnosis for a Recurrence-Risk Family.

Background: Primary carnitine deficiency (PCD) is a treatable autosomal recessive disorder caused by SLC22A5 gene variants and included in newborn screening widely. However, its prevalence and variant spectrum vary greatly, and prenatal diagnosis for recurrence-risk families remains rare. This study assessed tandem mass spectrometry (MS/MS) combined with genetic testing in NBS and prenatal diagnosis of PCD in Yancheng, China, and described the local prevalence and variant characteristics.

Methods: From 2015 to 2024, free carnitine (C0) levels were measured in neonatal dried blood spot (DBS) samples by MS/MS for PCD screening. Newborns with persistently low C0 levels were recalled for diagnostic evaluation. At diagnosis, the C0 levels in both neonatal and maternal blood were measured, and next-generation sequencing was performed for SLC22A5 variants in the newborns. For the recurrence-risk family with a previous proband, Sanger sequencing was used to confirm the parental origin of the proband's variants, and prenatal diagnosis with amniotic fluid was performed in the subsequent pregnancy.

Results: Combined MS/MS and genetic testing led to the diagnosis of 17 newborns with PCD (15 molecularly confirmed with biochemical results, two clinically inferred) and three newborns with maternal carnitine deficiency among the 152 newborns with persistently low C0 levels on re-screening. In these 17 PCD newborns, 10 distinct variant sites were detected, of which missense variants predominated, with c.1400C>G (p.S467C) being the most frequent (13/32, 40.63%). For the proband in this recurrence-risk family, the two pathogenic variants were inherited from each parent. The fetus carried only the maternal variant, without postnatal anomalies.

Conclusion: NBS using MS/MS combined with genetic testing facilitates early diagnosis and classification of PCD. The screening-detected prevalence of PCD in Yancheng was 1:25,852, with c.1400C>G (p.S467C) as the hotspot variant. Genetic testing of SLC22A5 provided effective prenatal diagnosis for the recurrence-risk family.