基底膜α(Ⅳ)链染色正常的Alport综合征基因突变特点

COL4A5 mutation in an Alport syndrome boy with normal α(Ⅳ) chains of basement membranes

目的 检测、分析编码基底膜Ⅳ型胶原α5链基因COL4A5突变及其特点 ,正确理解α5 (Ⅳ )链免疫荧光学检查结果及意义。方法 报告 1例 7岁男性患儿 ,血尿半年 ,肾功能、听力及眼部检查均正常 ;肾脏病理电镜示基底膜大部分均匀变薄 ;有血尿、肾功能不全家族史。应用间接免疫荧光学方法检测该患儿肾脏基底膜α3(Ⅳ )、α4 (Ⅳ )和α5 (Ⅳ )链以及皮肤基底膜α5 (Ⅳ )链。应用逆转录 聚合酶链反应和直接测序的方法分析α5 (Ⅳ )链mR NA ,应用PCR和直接测序方法分析COL4A5基因。结果 患儿肾小球基底膜α3(Ⅳ )、α4 (Ⅳ )和α5 (Ⅳ )链以及皮肤基底膜α5 (Ⅳ )链染色均正常。mRNA和基因组DNA分析均证实碱基替代突变 (917G >A) ,导致α5链第 2 39位甘氨酸被精氨酸取代 ,为新发现的突变。结论 首次报道了皮肤和肾小球基底膜α5 (Ⅳ )链染色正常 (阳性 )的我国X连锁型Alport综合征男性患者COL4A5基因突变及特点。提示应正确应用和理解基底膜α5 (Ⅳ )链免疫荧光学检查结果 ,X连锁型Alport综合征男性患者皮肤和肾小球基底膜α5 (Ⅳ )链染色即便正常 (阳性 ) ,当家族史及其它临床资料仍怀疑Alport综合征时 ,应进行COL4A5基因的检测和分析。

Objective To understand the result and interpretation of α5(Ⅳ) chain staining by immunofluorescence.Methods A 7 year old boy with a familial history of hematuria presented persistent microscopic hematuria and normal renal function,but was normal in audiogram and ophthalmologic examination.Electron microscopy revealed diffuse glomerular basement membrane thinning.Immunofluorescent staining with anti α(Ⅳ) chains antibodies was performed on the epidermal and glomerular basement membranes.The α5(Ⅳ) chain mRNA was isolated from the cultured skin fibroblasts and analyzed by reverse transcription reaction and direct sequencing.Meanwhile,mutation analysis of the COL4A5 gene was performed by PCR and direct sequencing.Results Immunofluorescent disclosed continuous linear staining along epidermal basement membrane with anti α5(Ⅳ) antibody,and the continuous linear staining along glomerular basement membrane with anti α3(Ⅳ),α4(Ⅳ) and α5(Ⅳ) antibodies.A noval mutation (917G>A) in the COL4A5 gene was detected both at the RNA level and the genomic DNA level,and was confirmed to be causative by its absence in 100 control chromosomes.Conclusion For the first time in China,a COL4A5 gene mutation was detected in an X linked Alport syndrome boy with normal immunohistochemical distribution of type IV collagen α3～5 chains in epidermal and glomerular basement membranes.The findings indicate that the results of skin biopsy should be clearly delineated;and when a family history and clinical findings suggest having X linked Alport syndrome,mutation analysis of COL4A5 gene is advisable in male patients with normal expression of type Ⅳ collagen chains in basement membranes.