一例晚期婴儿型异染性脑白质营养不良病患儿的ARSA基因变异分析

目的分析1例晚期婴儿型异染性脑白质营养不良病(metachromatic leukodystrophy,MLD)患儿芳基硫酸酯酶A(arylsulfatase A,ARSA)编码基因的变异情况。方法应用Sanger测序方法检测ARSA基因第1~8共8个外显子序列。用PubMed Protein BLAST分析ARSA的跨种属保守性;应用Ucsf chimera软件对正常结构及变异结构的ARSA进行蛋白质3D结构建模及比对来分析变异所致的蛋白二级结构的丧失及蛋白空间结构的改变;应用PolyPhen-2、Mutation Taster及SIFT软件对新变异进行功能预测。结果患儿携带ARSA基因第3外显子c.467G>A(p.Gly156Asp)和第5外显子c.960G>A(p.Trp320*)复合杂合变异。c.467G>A(p.Gly156Asp)变异经PolyPhen-2、Mutation Taster、SIFT及PROVEAN预测软件预测为可能有害变异,同时经PubMed Protein BLAST分析ARSA第156位Gly在各种属间均高度保守,该氨基酸改变可导致编码的ARSA功能发生障碍;c.960G>A(p.Trp320*)变异经Ucsf chimera软件进行蛋白3D结构建模分析发现,该变异可导致编码蛋白空间结构严重变形,原有功能丧失。结论ARSA基因c.467G>A(p.Gly156Asp)和c.960G>A(p.Trp320*)复合杂合变异可能为该患儿罹患MLD的致病原因,基因变异检测结果可以为家系的遗传咨询和产前诊断提供依据。

Analysis of ARSA gene variant in an infant with late infantile metachromatic leukodystrophy

Objective To detect pathogenic variant of ARSA gene in an infant with late infantile metachromatic leukodystrophy(MLD).Methods The male proband had an onset of walking dysfunction and seizure at 28 months.Arylsulfatase A activity of his peripheral blood leucocytes was 26.9 nmol/mg.17h,and cranial MRI showed wild symmetrical demyelination.With genomic DNA extracted from his peripheral blood sample,all coding exons and splicing sites of the ARSA gene were subjected to Sanger sequencing.PubMed Protein BLAST system was employed to analyze cross-species conservation of the mutant amino acid.Ucsf chimera software was used to analyze the impact of candidate variants on the secondary structure of the protein product.Impact of potential variants was also analyzed with software including PolyPhen-2,Mutation Taster,SIFT and PROVEAN.Whole-exome sequencing was carried out to identify additional variants which may explain the patient’s condition.Results The proband was found to harbor compound heterozygous variants of the ARSA genec.467G>A(p.Gly156Asp)and c.960G>A(p.Trp320*)],neither of which was reported previously.As predicted by Ucsf chimera software,the c.960G>A(p.Trp320*)variant may demolish important secondary structures includingα-helix,β-strand and coil of the ARSA protein,causing serious damage to its structure and loss of function.The c.467G>A(p.Gly156Asp)variant was predicted to be"probably damaging"by PolyPhen-2,Mutation Taster and SIFT software.Conclusion The patient’s condition may be attributed to the compound heterozygous c.467G>A(p.Gly156Asp)and c.960G>A(p.Trp320*)variants of the ARSA gene.Above results have facilitated genetic counseling and prenatal diagnosis for this family.