四例Prader-Willi综合征患儿的分子遗传缺陷分析

目的 观察Pradet-Willi综合征(PWS)患者的分子遗传基础及临床筛查策略,为进一步的遗传咨询提供信息。方法 应用甲基化特异性PCR(MSPCR)及荧光原位杂交(FISH)技术对4例临床诊断PWS患者进行基因分析研究。结果 4例患者MSPCR结果均显示缺乏父源的相关片段,而仅为母源DNA,即第15号染色体母源单亲二体(matUPD15);FISH检测发现2例15q近端SNRPN基因片段的微小缺失。结论 父源15q11-13特异区带缺失及matUPD15亦与我国PWS患者致病的分子病理缺陷有关。临床开展相关的细胞分子遗传学实验诊断对PWS临床诊断及遗传咨询、产前诊断都具有积极的作用。

Prader-Willi syndrome and genomic imprinting

Objective Prader Willi syndrome (PWS) is an example of a human genetic disorder that involves imprinting genes on the proximal long arm of chromosome 15 and SNRPN gene as a candidate gene for this syndrome. The purpose of this study was to show the molecular genetic defects and genomic imprinting basis in Chinese PWS patients and to evaluate the clinical applications of a differential diagnostic test for PWS. Methods Fluorescence in situ hybridiezation (FISH) and methylation specific PCR (MSPCR) techniques were applied for 4 clinically suspected PWS patients. Using three probes, including SNRPN probe for identification of the critical locus in PWS region, D15Z1 and PML control probes for identification of the 15p arm and 15q arm, the authors detected the deletions 15q in PWS. MSPCR was based on sodium bisulfite treatment of DNA and PCR primers specific for the maternal and paternal allele. Results When hybridized with mixed probes, it was found in 2 patients that the central specific signal was absent, but both the flanking control signals were retained, indicating SNRPN gene deletion of chromosome 15q11 13. Bisulfite modified DNA from all PWS children amplified with methylated allele specific primer pair showed only maternal 131bp PCR product, indicating the maternal uniparental disomy (UPD15). Conclusion Genomic imprinting plays an important role in the molecular pathogenesis of PWS that caused by paternal microdeletions of 15q11 q13 or maternal UPD of chromosome 15. The basic defect seemed to be an absence of function of PWS genes that are normally expressed only from the paternal chromosome 15. MSPCR is a rapid and simple PCR based assay compared with other cyto molecular tests and its results were consistent with the clinical diagnosis of PWS, so it seems to be a reliable diagnostic method for PWS patients who show abnormal methylation at SNRPN. The genetic differential tests for PWS are important in determining familial recurrence risk.