线粒体tRNA Thr T15943C突变可能是影响耳聋相关12s rRNA A1555G突变表型表达的新突变位点

Mitochondrial tRNAThr T15943C mutation may be a new position that affects the phenotypic expression of deafness associated 12s rRNA A1555G mutation

目的通过对一个中国汉族耳聋塞系进行分析研究，探索与耳聋相关的新的继发突变位点。方法对一个中国汉族耳聋家系进行临床和分子遗传学特征分析，然后建立永生化淋巴母细胞系，从细胞倍增时间和活性氧等部分功能实验方面进行验证。结果家系内听力下降的母系成员在听力损失程度和听力曲线方面存在差异。该家系耳聋外显率较高，包括药物致聋的耳聋外显率为66．7％，而非药物致聋的外显率为44．4％。对先证者及母系成员进行线粒体DNA全序列分析，发现除了12s rRNA A1555G和tRNA Thr T15943C突变位点外，其余33个均为已报道的多态性位点。进一步的单体型进化树分析发现，该家系属于东亚线粒体单体型F。15943位点位于tRNA Thr茎结构上，该位点发生T-C碱基变化时会破坏tRNAn Thr 二级结构上十分保守的T-A碱基对。细胞功能实验表明，与相同F单体型的正常对照组和仅携带12s rRNA A1555G单突变家系相比，该双突变耳聋家系永生细胞系的细胞倍增时间均较其他两个对照组延长，活性氧水平则增高。结论线粒体tRNA Thr T15943C突变可能作为潜在的修饰因子与12s rRNA A1555G突变相互作用，从而增强耳聋外显率和表现度。

Objective To identify secondary mutations associated with deafness in a Chinese family affected with deafness. Methods The family has been subjected to clinical and molecular analyses, in addition with measurement of reactive oxygen species and doubling time after establishment of immortalized lymphocyte cell lines. Results The results showed that the hearing loss level and audiometric configuration were discrepant among the family members with maternally transmitted hearing loss. The penetrance of hearing loss in this family was respectively 66.7% and 44. 4% when aminoglycoside-induced hearing loss was included or excluded. Analysis of whole mitochondrial genome has found 33 variants as previously reported polymorphisms, except for a 12s rRNA A1555G mutation and a tRNAThr T15943C mutation. Haplotype evolutionary tree has verified that this family belonged to East-Asian haplogroup F. 15943 position was located on the T-stem of the tRNAThr , which has destroyed the extremely conserved T-A base pair when T changed to C at this position. However, functional experiments indicated that the population doubling time in special galactose and glucose were longer, whilst the level of reactive oxygen species has increased. Compared with the control cell line groups and a family only carrying the 12s rRNA A1555G mutation, all of the three groups belonged to the same haplogroup. Conclusion Mitochondrial tRNAThr T15943C mutation may act as a potential modifying factor and interact with 12s rRNA A1555G mutation, and thereby enhance the penetrance and expression of deafness.