多重竞争性荧光PCR检测X连锁Alport综合征大片段缺失突变

Detection of large deletions in X linked Alport syndrome using competitive multiplex fluorescence polymerase chain reaction

目的:探讨多重竞争性荧光PCR在X连锁Alport综合征分子诊断中的应用。方法:选择20例在北京大学第一医院确诊且未进行基因诊断的X连锁Alport综合征患者为研究对象,同时选择2例经多重连接依赖性探针扩增技术检测到COL4A5基因大片段缺失突变的患者作为阳性对照和1例经肾活检组织电子显微镜检查证实非Alport综合征的男性作为正常对照。首先应用多重竞争性荧光PCR技术扩增COL4A5基因53个外显子和4个参照基因,对于检测到COL4A5基因缺失第1外显子者,进而应用相同技术扩增COL4A5基因外显子1~4、COL4A6基因外显子1~4、两基因共用启动子以及3个参照基因;对于检测到拷贝数缺失者,应用琼脂糖凝胶电泳鉴定扩增后的PCR产物或直接测序。结果:两例阳性对照应用多重竞争性荧光PCR技术检测到的COL4A5基因缺失突变与应用多重连接依赖性探针扩增技术检测到的COL4A5基因缺失突变一致。20例患者中6例(30%)明确了基因型,其中2例患者具有累及COL4A5和COL4A6两个基因5'端的大片段缺失,2例患者具有累及COL4A5基因30个外显子以上的大片段缺失,1例患者具有累及COL4A5基因至少1个外显子的大片段缺失,1例患者具有COL4A5基因缺失13个碱基的小的缺失突变,未检测到重复突变。结论:多重竞争性荧光PCR技术可用于检测X连锁Alport综合征大片段缺失突变,是对该病分子诊断检测方法的重要补充。

Objective: To evaluate the ability of multiplex competitive fluorescence polymerase chain reaction in detection of large deletion and duplication genotypes of X-linked Alport syndrome. Methods:Clinical diagnosis of X-linked Alport syndrome was based on either abnormal staining of type Ⅳ collagenα5 chain in the epidermal basement membrane alone or with abnormal staining of type Ⅳ collagen α5chain in the glomerular basement membrane and Bowman's capsule/ultrastructural changes in the glomerular basement membrane typical of Alport syndrome. A total of 20 unrelated Chinese patients( 13 males and 7 females) clinically diagnosed as X-linked Alport syndrome were included in the study. Their genotypes were unknown. Control subjects included a male patient with other renal disease and two patients who had large deletions in COL4A5 gene detected by multiplex ligation-dependent probe amplification. Genomic DNA was isolated from peripheral blood leukocytes in all the participants. Multiplex competitive fluorescence polymerase chain reaction was used to coamplify 53 exons of COL4A5 gene and four reference genes in a single reaction. When a deletion removed exon 1 of COL4A5 gene was identified,the same method was used to coamplify the first 4 exons of COL4A5 and COL4A6 genes,a promoter shared by COL4A5 and COL4A6 genes,and three reference genes in a single reaction. Any copy number loss suggested by this method was verified by electrophoresis of corresponding polymerase chain reaction amplified products or DNA sequencing to exclude possible DNA variations in the primer regions. Results: Genotypes of two positive controls identified by multiplex competitive fluorescence polymerase chain reaction were consistent with those detected by multiplex ligation-dependent probe amplification. Deletions were identified in 6 of the 20 patients,including two large deletions removing the 5' part of both COL4A5 and COL4A6 genes with the breakpoint located in the second intron of COL4A6,two large deletions removing more than 30 exons of COL4A5 gene,one large deletion removing at least 1 exon of COL4A5 gene,and one small deletion involving 13 bps. No duplication was found. Conclusion: Our results show that multiplex competitive fluorescence polymerase chain reaction is a good alternative to classical techniques for large deletion genotyping in X-linked Alport syndrome.