一例Ia型先天性糖基化障碍病患儿的PMM2基因变异分析

Analysis of PMM2 gene variant in an infant with congenital disorders of glycosylation type 1a

目的鉴定1例Ia型先天性糖基化障碍病(congenital disorders of glycosylation type 1a,CDG-1a)患儿PMM2基因的致病性变异。方法应用PCR技术扩增其PMM2基因的编码区及相关剪切位点序列,并对PCR产物进行直接测序。参考ESP及SNP数据库对结果进行比对。利用protein BLAST系统分析突变氨基酸的跨种属保守性;利用PubMed BLAST CD-search系统分析PMM2蛋白结构缺失所丧失的蛋白功能域;用PolyPhen-2、SIFT及Mutation Taster软件对新变异进行功能预测。用全外显子基因组测序法明确患儿有无存在其他可疑变异。结果患儿携带PMM2基因c. 458_462delTAAGA(p. Ile153*)和c. 395T>C(p. Ile132Thr)复合杂合变异;患儿父亲携带c.458_462delTAAGA杂合变异,患儿母亲携带c.395T>C杂合变异。其中c. 458_462delTAAGA(p. Ile153*)为未报道过的新变异,经PubMed BLAST CD-search系统分析其编码的PMM2蛋白结构存在10个蛋白功能域的丧失,生物活性被严重破坏,预测为可能有害变异;c.395T>C(p.Ile132Thr)在SNP数据库有收录,经功能预测为可能有害变异。经全外显子基因组测序明确患儿除存在上述PMM2基因变异外不存在其他可疑变异。结论PMM2基因c. 458_462delTAAGA(p.Ile153*)和c.395T>C(p.Ile132Thr)复合杂合变异可能为患儿的致病原因,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。

Objective To identify potential mutation of PMM2 gene in an infant with congenital disorders of glycosylation type 1a (CDG-1a). Methods Genomic DNA was extracted from peripheral blood sample of the patient. All coding exons (exons 1-8) and splicing sites of the PMM2 gene were amplified with PCR. Potential variants were detected by direct sequencing of the PCR products and comparing the results against the ESP and SNP human gene databases. A protein BLAST system was employed to analyze cross-species conservation of the variants amino acid. A PubMed BLAST CD-search system was employed to identify functional domains damaged by variants of the PMM2 gene. Impact of potential variants was analyzed using software including PolyPhen-2 SIFT and Mutation Taster. Whole exome sequencing was used to identify additional variants of the PMM2 gene which may explain the condition of the patient. Results The child was found to carry compound heterozygous variants (c.458_462delTAAGA and c. 395T>C) of the PMM2 gene, which were inherited respectively from his father and mother. The c. 458_462delTAAGA has not been reported previously and may result in disruption of 10 functional domains within the PMM2 protein. The c. 395T>C mutation has been recorded by a SNP database with frequency unknown. Both mutations were predicted as "probably damaging". Whole exome sequencing has identified no additional disease-causing variant which can explain the patient’s condition. Conclusion The patient’s condition may be attributed to the compound heterozygous variants c. 458_462delTAAGA and c. 395T>C of the PMM2 gene. Above results has facilitated molecular diagnosis for the patient .