Objectives: Primary carnitine deficiency (PCD) is a rare fatty acid metabolism disorder that can cause neonatal death. This study aims to analyze carnitine levels and detect SLC22A5 gene in newborns with carnitine deficiency, to provide a basis for early diagnosis of PCD, and to explore the relationship between carnitine in blood and SLC22A5 genotype.
Methods: A total of 40 neonates with low free carnitine (C0<10 μmol/L) in blood were the subjects of the study. SLC22A5 gene was detected by Sanger sequencing to analyze the value of carnitine, the results of gene test and their relationship.
Results: A total of 15 variants of SLC22A5 gene were detected, including 11 pathogenic or likely pathogenic variants and 4 variants of uncertain significance. There were 5 new mutations: c.288delG (p.G96fsX33), c.744_745insTCG (p.M258_L259insS), c.752A>G (p.Y251C), c.495 C>A (p.R165E), and c.1298T>C (p.M433T). We found 14 PCD patients including 2 homozygous mutations and 12 heterozygous mutations, 14 with 1 mutation, and 12 with no mutation among 40 children. The C0 concentration of children with SLC22A5 gene homozygous or complex heterozygous mutations was (4.95±1.62) μmol/L in the initial screening, and (3.90±1.33) μmol/L in the second screening. The C0 concentration of children with no mutation was (7.04±2.05) μmol/L in the initial screening, and (8.02±2.87) μmol/L in the second screening. There were significant differences between children with homozygous or compound heterozygous mutations and with no mutation in C0 concentration of the initial and the second screening (both P<0.05), as well as between children with truncated mutation and with untruncated mutation in C0 concentration of the initial screening (P=0.022).
Conclusions: There are 5 new mutations which enriched the mutation spectrum of SLC22A5 gene. C0<5 μmol/L is highly correlated with SLC22A5 gene homozygous or compound heterozygous mutations. Children with truncated mutation may have lower C0 concentration than that with untruncated mutation in the initial screening.
目的: 原发性肉碱缺乏症(primary carnitine deficiency，PCD)是一种罕见的可致新生儿死亡的脂肪酸代谢紊乱性疾病。本研究对新生儿足跟血行串联质谱分析筛查出的肉碱缺乏儿，进一步行血肉碱水平分析及SLC22A5基因检测，为PCD的早期诊断提供依据，同时探索血肉碱水平与SLC22A5基因型的关系。方法: 收集新生儿血串联质谱筛查游离肉碱(free carnitine，C0)值<10 μmol/L的40例患儿为研究对象，用Sanger测序方法对PCD的致病基因SLC22A5基因进行检测，分析肉碱水平、基因检测结果及两者的关系。结果: 共检出SLC22A5基因变异15种(42个)，包括11种致病或可能致病变异和4种意义不明变异。发现c.288delG(p.G96fsX33)，c.744_745insTCG(p.M258_L259insS)，c.752A>G(p.Y251C)，c.495C>A(p.R165E)，c.1298T>C(p.M433T)5种新突变。在40例串联质谱初筛肉碱缺乏的患儿中，14例被确诊为PCD，包括SLC22A5基因纯合突变2例，复合杂合突变12例；14例检出1个SLC22A5基因突变；12例未检出SLC22A5基因突变。确诊为PCD的患儿初筛C0值为(4.95±1.62) μmol/L，复查C0值为(3.90±1.33) μmol/L；未检出突变的患儿初筛C0值为(7.04±2.05) μmol/L，复查C0值为(8.02±2.87) μmol/L，确诊为PCD的患儿与未检出突变患儿的初筛及复查C0值差异均有统计学意义(均P<0.05)；检出截短突变的患儿与未检出截短突变的患儿初筛C0值差异有统计学意义(P=0.022)。结论: 发现的5种新突变丰富了SLC22A5基因突变谱；新生儿足跟血串联质谱初筛C0值<5 μmol/L与SLC22A5基因纯合或复合杂合突变型具有更强的相关性；具有截短突变的患儿较不含截短突变患儿的C0值可能更低。.
Keywords: SLC22A5; free carnitine in blood; gene mutation; neonatal blood screening with tandem mass spectrometry; primary carnitine deficiency.