Analysis of genotypes and biochemical phenotypes of neonates with abnormal metabolism of butyrylcarnitine.

Objectives: To investigate the genotypes and biochemical phenotypes of neonates with abnormal metabolism of butyrylcarnitine (C4).

Methods: One hundred and twenty neonates with increased C4 levels detected by tandem mass spectrometry in the neonatal screening at Children's Hospital, Zhejiang University School of Medicine from January 2018 to June 2023 were included. The initial screening data and recalled data of C4 and C4/C3 were collected and converted into multiples of C4 reference range. Next generation sequencing was performed and the exons with adjacent 50 bp regions of and genes were captured by liquid phase capture technique. Variant information was obtained by bioinformatic analysis and the pathogenicity were classified according to the American College of Medical Genetics and Genomics criteria. The Wilcoxon rank sum test was used to analyze the differences in C4 levels among neonates with different variation types.

Results: In total, 32 variants in gene were detected, of which 7 variants were reported for the first time; while 41 variants of gene were detected, of which 17 variants have not been previously reported. There were 39 cases with biallelic variations and 3 cases with monoallelic variations; 34 cases with biallelic variations and 36 cases with monoallelic variations. Furthermore, 5 cases were detected with both and gene variations. Inter group comparison showed that the multiples of C4 reference range in initial screening and re-examination of the biallelic variations and biallelic variations groups were significantly higher than those of the monoallelic variations group (all <0.01), while the multiples in the biallelic variations group were significantly higher than those in the biallelic variations group (all <0.01). The multiples of C4 reference range in the initial screening greater than 1.5 times were observed in all neonates carrying or biallelic variations, while only 25% (9/36) in neonates carrying monoallelic variations.

Conclusions: and/or gene variants are the main genetic causes for elevated C4 in newborns in Zhejiang region with high genotypic heterogeneity. The C4 levels of neonates with biallelic variations are significantly higher than those of neonates with monoallelic variations. The cut-off value for C4 level could be modestly elevated, which could reduce the false positive rate in tandem mass spectrometry neonatal screening.