一个中国汉族人家族性激素耐药型肾病综合征家系NPHS2基因新突变

目的　分析中国汉族人家族性激素耐药型肾病综合征 (SRNS)家系NPHS2基因及突变特点。方法　研究对象为一个中国汉族人家族性SRNS家系中的先证者及其兄和父母 ,对照人群为 5 3例尿检正常成年人。取肾组织做常规光镜检查和 podocin、nephrin、α actinin、WT1表达的检查。提取外周血白细胞基因组DNA ,PCR扩增NPHS2基因 8个外显子 ;应用变性高效液相色谱(DHPLC)分析PCR产物 ,对DHPLC洗脱曲线异常者进行DNA序列测定。结果　先证者及其兄肾脏病理示 :局灶节段性肾小球硬化。先证者肾组织 podocin重组蛋白P35染色弱阳性 ,P2 1染色阴性 ;nephrin、α actinin和WT1染色的范围、定位、分布和荧光强度与对照组无差异。DHPLC示先证者及其父母洗脱曲线异常 ;DNA测序证实先证者为 4 6 7_4 6 8insT与 5 0 3G >A复合杂合突变 ,其父为 5 0 3G >A杂合突变 ,其母为 4 6 7_4 6 8insT杂合突变。结论　首次发现了一中国汉族人家族性SRNS家系中NPHS2基因突变——— 4 6 7_4 6 8insT与 5 0 3G >A复合杂合突变 ,且 5 0 3G >A突变为新发现的突变 ;同时还发现该复合杂合突变引起肾组织中抗 podocin重组蛋白P35的染色明显减弱 ,抗 podocin重组蛋白P2 1的染色阴性。

A novel mutation of NPHS2 identified in a Chinese family with steroid-resistant nephrotic syndrome

OBJECTIVE: Autosomal recessive steroid-resistant nephrotic syndrome (SRNS) is a subgroup of familial nephrotic syndrome. A causative gene has been identified, that is NPHS2, in chromosome 1q25-31, which encodes podocin. This study aimed to detect NPHS2 mutation in a Chinese family with SRNS. METHODS: Renal biopsy was performed on the proband and her sibling for routine histologic and immunohistochemical investigation and electron microscopic examination. The expressions of podocin, nephrin, alpha-actinin and WT1 in glomeruli of the proband were detected by indirect immunofluorescence. Peripheral blood samples were collected for genetic analysis from the proband and her parents, and 53 adults with normal urinalysis. Genomic DNA was isolated from peripheral blood leucocytes. Eight exons of NPHS2 were amplified by polymerase chain reaction. Mutational analysis was performed using denaturing high-performance liquid chromatography (DHPLC) and DNA fragments with aberrant elution profiles of both strands revealed by DHPLC were re-amplified and sequenced directly. RESULTS: The histologic findings on kidney biopsies were focal segmental glomerulosclerosis. In controls, the distribution of staining with P35, rabbit against a human podocin recombinant protein (amino acids 135 - 383 = all the C-terminal part of the protein downstream the transmembrane domain), and P21, rabbit against a human podocin recombinant protein (amino acids 15 - 89 = all the N-terminal part of the protein upstream the transmembrane domain) showed a linear pattern along glomerular capillary walls on glomeruli, and the fluorescent intensity of the staining with P35 was intensely positive. The fluorescent intensity of the staining with P21 was positive. In the proband, the distribution of the staining with P35 showed uneven and nonlinear, and the fluorescent intensity of the staining with P35 was weakly positive. The staining with P21 was negative. The area, location, distribution and fluorescent intensity of the staining with nephrin, alpha-actinin and WT1 on glomeruli of the proband were the same as those in the controls. The DHPLC elution profiles of exon 4 of NPHS2 from the proband and her parent were aberrant. The chromatograms by sequencing detected in the exon 4 of NPHS2 showed a composite heterozygous mutation of both 467_468insT and 503G > A in the proband, a heterozygous mutation of 503G > A in her father, and a heterozygous mutation of 467_468insT in her mother, respectively. CONCLUSION: The study demonstrated for the first time a novel mutation, 503G > A, of NPHS2 in Chinese kindred with autosomal recessive SRNS. A significantly decreased or negative expression was also revealed in glomeruli of the proband stained with two kinds of anti-podocin antibodies.