A Study of Maternal Patients Diagnosed with Inborn Errors of Metabolism Due to Positive Newborn Mass Screening in Their Newborns

Background: There are reports of mothers being diagnosed with inborn errors of metabolism (IEM) via positive newborn screening (NBS) of their newborns. Mothers with IEM are often considered to have mild cases of little pathological significance. Based in Niigata Prefecture, this study aimed to investigate mothers newly diagnosed with IEM via positive NBS in their newborns using tandem mass spectrometry, and to clarify the disease frequency and severity. Methods: This was a single-institution, population-based, retrospective study. The subjects were mothers whose newborns had false-positive NBS, among 80,410 newborns who underwent NBS between April 2016 and May 2021. Result: there were 3 new mothers were diagnosed with IEM (2 with primary systemic carnitine deficiency (PCD) and 1 with 3-methylcrotonyl-CoA carboxylase deficiency) out of 5 who underwent examination among 18 false positives. The opportunity for diagnosis was low C0 and high C5-OH acylcarnitine levels in their newborn. Two novel SLC22A5 variants (c.1063T > C/c.1266A > G) were identified in patients with PCD. None of the patients had any complications at the time of diagnosis, but two patients showed improvement in fatigue and headache after taking oral carnitine. Conclusion: New mothers with IEM cannot be considered as mild cases and need to be treated when necessary. The two novel SLC22A5 variants further expand the variant spectrum of PCD.