Objective: To investigate the genetic characterization of 3-hydroxyisovalerylcarnitine (C5-OH) metabolic abnormality in neonates.
Methods: Fifty two newborns with increased C5-OH, C5-OH/C3 and C5-OH/C8 detected by tandem mass spectrometry during neonatal screening were enrolled in the study. Genomic DNA was extracted from the whole blood samples of 52 cases and their parents. Seventy-nine genes associated with genetic and metabolic diseases including MCCC1, MCCC2 were targeted by liquid capture technique. Variation information of these genes was examined by high-throughput sequencing and bioinformatic analysis, and then was classified based on the American College of Medical Genetics and Genomics (ACMG) standards and guidelines. The genetic types were classified as wild-type, MCCC1-maternal-mutation, MCCC1-paternal-mutation and MCCC2-mutation. Wilcoxon rank-sum test was performed for the increased multiples of C5-OH calculated in neonatal screening.
Results: Twenty one MCCC1 variants (14 novel) were identified in 37 cases, 6 MCCC2 variants (5 novel) in 4 cases. The increased multiple of C5-OH calculated in MCCC1-maternal-mutation and MCCC2-mutation groups were significantly higher than that in wild-type group (all P<0.05), while there was no significant difference between MCCC1-paternal-mutation group and wild-type group (P>0.05).
Conclusions: Mutations on MCCC1 and MCCC2 genes are the major genetic causes for the increased C5-OH in neonates, and maternal single heterozygous mutation can contribute to the moderately to severely increased C5-OH.
目的: 探讨新生儿3-羟基异戊酰基肉碱（C5-OH）代谢异常的遗传学原因。
方法: 收集2018年1月至12月在浙江省新生儿遗传代谢病筛查中心经串联质谱法筛查结果为C5-OH增高的52例新生儿的资料，包括新生儿筛查与复查随访的C5-OH、C5-OH/C3、C5-OH/C8检测数据，并换算成C5-OH增高倍数。采用液相捕获技术靶向捕获 MCCC1、 MCCC2等79个遗传代谢病相关基因，通过高通量测序和生物信息学分析获取基因的突变信息，参考美国医学遗传学与基因组学学会（ACMG）分类标准进行分级。依据基因检测情况，将C5-OH增高新生儿分为未检出突变组、 MCCC1母源突变组、 MCCC1父源突变组、 MCCC2突变组，采用威尔科克森秩和检验分析不同组间C5-OH增高倍数的差异。
结果: 37例检出 MCCC1突变，涉及21种突变型，其中14种为新发现的突变型；4例检出 MCCC2突变，涉及6种突变型，其中5种为新发现的突变型。 MCCC1母源突变组、 MCCC2突变组的C5-OH增高倍数均高于未检出突变组（均 P < 0.05）， MCCC1父源突变组的C5-OH增高倍数与未检出突变组差异无统计学意义（ P>0.05）。
结论: MCCC1、 MCCC2基因突变是导致新生儿血C5-OH增高的主要遗传学原因，其中母源性单杂合突变可导致中重度C5-OH增高。