Detection of COL4A5 gene mutations in Chinese patients with Alport's syndrome

Nephrol Dial Transplant 2004; 19(5):     

Detection of COL4A5 gene mutations in Chinese patients with Alport's syndrome.

BACKGROUND: Mutations in the COL4A5 gene, encoding the alpha 5 chain of type IV collagen, are responsible for X-linked Alport's syndrome (XLAS), a progressive nephropathy characterized by glomerular basement membrane abnormalities and usually associated with progressive hearing loss and ocular lesions. METHODS: In this study, we analysed all 51 exons of the COL4A5 gene in 20 Chinese patients with XLAS or suspected XLAS from 16 families by using polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) DNA sequencing. RESULTS: Five gene mutations identified in five families were considered to be pathogenic, including one nonsense mutation in exon 1 (266C-->T, Gln22Term), two missense mutations in exons 31 (2757G-->T, Gly852Val) and 43 (4142C-->T, Pro1314Ser), and two splice site mutations in introns 1 and 25 just next to the 3' end of their respective exons (283+1G-->T, 2150+1G-->T). According to GenBank, these five mutations have not been reported previously. All male patients have typical clinical manifestations and pathological findings that closely correspond to the effects of the mutations. Furthermore, seven gene polymorphisms were detected in introns 18 and 10 and exons 20, 27, 29, 39 and 46. Only the substitution in intron 18 (1234+25G-->A) had a gene frequency significantly higher in patients than in normal individuals. CONCLUSION: Our study demonstrated the critical role of COL4A5 gene mutations in the pathogenesis of XLAS. The linkage of the polymorphism to AS is still unknown.     

Mutational analysis of COL4A5 gene in Korean Alport syndrome

Mutational analysis of the COL4A5 gene in X-linked Alport syndrome (AS) requires an expensive and time-consuming procedure with a detection rate of 50%, at best. There have been three multicenter collaborative studies of mutation analysis in the COL4A5 gene using systematic screening of entire coding regions of the gene. This is a similar study executed in a single center in Korea. Twenty-five unrelated Korean patients with AS in whom the diagnosis was confirmed pathologically were included in the study. By systematic screening of all 51 exons of the gene using polymerase chain reaction/single-strand conformation polymorphism analysis, ten mutations were detected in 10 unrelated patients. These included one medium-sized deletion involving exon 49–51, one single base pair deletion, one nonsense point mutation, one splice site mutation, and six missense point mutations. Of the six missense mutations, four involved a glycine residue and disrupted the Gly-X-Y repeats in the collagenous domain. The overall detection rate of mutations was 40%. Although DNA analysis in AS is currently not applicable to routine clinical diagnosis due to several practical and technical problems, it is likely to replace morphological diagnosis in the near future. Received: 22 March 1999 / Revised: 21 May 1999 / Accepted: 21 May 1999     

Improved genetic counseling in Alport syndrome by new variants of COL4A5 gene

There are current requirements of using genetic databases for offering a better genetic assistance to patients of some syndromes, especially those with X‐linked heredity patterns (like Alport Syndrome) for the high probability of having descendants affected by the disease. We describe the first reported case of COL4A5 gene missense c.1499 G > T mutation in a 16‐year‐old girl confirmed to be affected by Alport Syndrome after genetic counseling. Next Generation Sequencing procedures let discover this mutation and offer an accurate clinical treatment to this patient. Current scientific understanding of genetic syndromes suggests the high importance of updated databases and the inclusion of Variant of Unknown Significance related to clinical cases. All of this updating could enable patients to have a better opportunity of diagnosis and having genetic and clinical counseling. This event is even more important in women planning to start a family to have correct genetic counseling regarding the risk posed to offspring, and allowing the decision to undergo prenatal testing.     

Sixteen novel mutations identified in COL4A3, COL4A4, and COL4A5 genes in Slovenian families with Alport syndrome and benign familial hematuria

Alport syndrome (ATS) and benign familial hematuria (BFH) are type IV collagen inherited disorders. Mutations in COL4A5 are generally believed to cause X-linked ATS, whereas mutations in COL4A3 and COL4A4 genes can be associated with the autosomal-recessive and -dominant type of ATS or BFH. In view of the wide spectrum of phenotypes, an exact diagnosis is sometimes difficult to achieve. This study involved screening each exon with boundary intronic sequences of COL4A3, COL4A4, and COL4A5 genes by optimized polymerase chain reaction-single-stranded conformational polymorphism analysis in 17 families with ATS and in 40 families diagnosed as having BFH. Twelve different mutations were found in the COL4A5 gene in ATS patients, comprising nine missense mutations, a splice site mutation, a mutation causing frameshift, and a nonsense mutation. One of the missense mutations (p.G624D) was present not only in one family with ATS but also in five families with suspected BFH. Three heterozygous mutations in the COL4A3 gene (two missense and one frameshift) and four heterozygous mutations in COL4A4 (two splice site, one in-frame deletion, and one missense) were identified in patients with BFH. Sixteen mutations are to the best of our knowledge new and private.     

Alport综合征一家系中新的COL4A5基因突变

目的了解我国Ｘ伴性显性（ＸＤ）遗传Ａｌｐｏｒｔ综合征（ＡＳ）中ＣＯＬ４Ａ５基因突变特点。方法应用聚合酶链反应（ＰＣＲ）－变性梯度凝胶电泳（ＤＧＧＥ）和直接测序的方法，对来自７个ＸＤ－ＡＳ家系１０个成员和１００个正常人外周血ＤＮＡ标本进行了ＣＯＬ４Ａ５基因４３号外显子的检测。结果在一个家系中发现４１４２Ｃ→Ｔ（Ｐｒｏ１３１４Ｓｅｒ）的转换突变，先证者与其弟、其母均发现有此异常。结论表明该突变为一遗传     

Deletions of the COL4A5 gene in patients with Alport syndrome.

Mutations in the COL4A5 gene encoding the alpha 5 chain of type IV collagen have been found in linkage with X-chromosomal Alport syndrome (AS). To identify COL4A5 mutations in patients from Germany with clinically defined AS, DNA from 20 unrelated patients was analyzed by conventional Southern blotting. By using full length alpha 5(IV) cDNA probes, large COL4A5 deletions could be detected in two patients. In one case, a 34 kb deletion affecting the 14 most 3' exons of the gene was observed. The second patient harbored a complete COL4A5 deletion. In both cases, functional alpha 5(IV) mRNA was unlikely to be present. Clinically, both patients developed end-stage renal failure before age 30. Furthermore, they had characteristic retinal flecks, and sensorineural hearing loss with typical changes on the audiogram. The patient with the complete deletion of COL4A5 lost the renal allograft due to an anti-GBM mediated glomerulonephritis.     

A female with X-linked Alport syndrome and compound heterozygous COL4A5 mutations

Background

Female subjects with X-linked Alport syndrome have a single COL4A5 mutation, germ cell mosaicism in affected tissues and typically develop renal failure later or less often than male subjects. Women with two mutations are exceedingly rare, and usually have consanguineous parents or uniparental disomy. We describe here a 20-year-old woman who inherited two different COL4A5 variants, one from her father (c.2677G>C) and one from her mother (c.384 +1 G>A).

Case-diagnosis/treatment

The index case had normal renal function, proteinuria and no clinically detectable hearing loss, or ocular abnormalities. Her father and paternal uncle developed end-stage renal disease at 37 and 28 years respectively, together with hearing loss, but not lenticonus or central retinopathy. Her mother had mildly impaired renal function, proteinuria, hearing loss, but no ocular abnormalities. Her maternal grandfather and 22-year-old brother, both with this mutation, developed renal failure by 28 years with hearing loss, or had proteinuria and hearing loss respectively.

Conclusion

The index case has clinical features consistent with germ cell mosaicism of two COL45A mutations associated with adult-onset renal failure, but no ocular abnormalities. Her risk of renal failure is high, but the rate of progression to end-stage disease depends on the underlying mutations, and disease modification with renin–angiotensin blockade.     

常染色体隐性遗传Alport 综合征一家系COL4A3及COL4A4基因突变分析

目的 通过对有近亲婚配史的Alport综合征一家系Ⅳ型胶原α3和α4链的 COL4A3/COL4A4 基因分析，明确常染色体隐性遗传Alport综合征的基因突变,为该病的基因诊断和家系遗传咨询提供更为全面的理论基础｡ 方法 PCR扩增先证者DNA COL4A3/COL4A4 基因的共98个外显子，经直接测序，寻找突变位点，对有意义的突变经限制性内切酶AvaⅡ酶切在家系中分析验证｡ 结果 在该患者中共发现1个错义突变和10个序列变异｡其中在COL4A3 基因上发现一个位于42号外显子上的错义突变 G3725A,导致蛋白质Gly1242Asp的突变｡错义突变在患者中是纯合子，携带者中是杂合子，其他正常家系成员及筛查100条正常人染色体，未发现该突变｡10个序列变异为单核苷酸多态性改变｡ 结论 报道了一个国内较少见的常染色体隐性遗传Alport 综合征家系，同时经基因突变筛查发现Ⅳ型胶原α3链的一个新的致病性的基因突变｡     

COL4A3/COL4A4 mutations: from familial hematuria to autosomal-dominant or recessive Alport syndrome

COL4A3/COL4A4 mutations: From familial hematuria to autosomal-dominant or recessive Alport syndrome. BACKGROUND: Mutations of the type IV collagen COL4A5 gene cause X-linked Alport syndrome (ATS). Mutations of COL4A3 and COL4A4 have been reported both in autosomal-recessive and autosomal-dominant ATS, as well as in benign familial hematuria (BFH). In the latter conditions, however, clinical features are less defined, few mutations have been reported, and other genes and non-genetic factors may be involved. METHODS: We analyzed 36 ATS patients for COL4A3 and COL4A4 mutations by polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) and direct sequencing. Sporadic patients who had tested negative for COL4A5 mutations were included with typical cases of autosomal recessive ATS to secure a better definition of the phenotype spectrum. RESULTS: We identified seven previously undescribed COL4A3 mutations: in two genetic compounds and three heterozygotes, and one in COL4A4. In agreement with the literature, some of the mutations of compound heterozygotes were associated with microhematuria in healthy heterozygous relatives. The mutations of heterozygous patients are likely dominant, since no change was identified in the second allele even by sequencing, and they are predicted to result in shortened or abnormal chains with a possible dominant-negative effect. In addition, both genes showed rare variants of unclear pathogenicity, and common polymorphisms that are shared in part with other populations. CONCLUSIONS: This study extends the mutation spectrum of COL4A3 and COL4A4 genes, and suggests a possible relationship between production of abnormal COL IV chains and dominant expression of a continuous spectrum of phenotypes, from ATS to BFH.     

Autosomal-dominant Alport syndrome: natural history of a disease due to COL4A3 or COL4A4 gene

BACKGROUND: Alport syndrome is a clinically and genetically heterogeneous nephropathy. The majority of cases are transmitted as an X-linked semidominant condition due to COL4A5 mutations. In this form males are more severely affected than females. Less than 10% of cases are autosomal recessive due to mutation in either COL4A3 or COL4A4. In this rarer form, both males and females are severely affected. Only two cases of autosomal-dominant Alport syndrome have been reported, one due to a COL4A3 mutation and the other due to a COL4A4 mutation. Because of the paucity of the reported families, the natural history of autosomal-dominant Alport syndrome is mostly unknown. METHODS: Four families with likely autosomal-dominant Alport syndrome were investigated. COL4A3 and COL4A4 genes were analyzed by denaturing high-performance liquid chromatography (HPLC). Automated sequencing was performed to identify the underlying mutation. RESULTS: Two families had a mutation in the COL4A4 gene and two in the COL4A3. Accurate clinical evaluation of family members showed interesting results. Affected individuals (22 persons) had a wide range of phenotypes from end-stage renal disease (ESRD) in the fifth decade to a nonprogressive isolated microhematuria. Finally, three heterozygous individuals (90, 22 and 11 years old, respectively) were completely asymptomatic. CONCLUSION: This paper demonstrated that patients affected by autosomal-dominant Alport syndrome have a high clinical variability. Moreover, a reduced penetrance of about 90% (3 of 25) may be considered for the assessment of recurrence risk during genetic counseling of these families.     

Long-term effects of cyclosporine A in Alport's syndrome

BACKGROUND: In 1991, our initial results of cyclosporine A (CsA) administration in eight patients with Alport's syndrome were published. A significant decrease in or disappearance of proteinuria and apparently good tolerance to CsA were observed in all patients. METHODS: CsA administration has been maintained in these eight patients with the aim of obtaining further information about the clinical course of the disease. The ages of these eight patients currently range from 15 to 27 years, and the mean duration of treatment is from 7 to 10 years (x = 8.4 years). RESULTS: Renal function has remained stable, with no evaluable changes in serum creatinine levels compared with pre-CsA treatment values. Proteinuria in all patients has either remained negative or are values far lower than pretreatment levels. A second renal biopsy was performed in all patients after five years of CsA administration. No aggravation of the lesion present at the first biopsy or lesions typical of cyclosporine intoxication was observed. CONCLUSIONS: After a mean duration of 8.4 years and with no deterioration in renal function, we found possible beneficial effects of the continued treatment of CsA in patients with Alport's syndrome who present evidence of progression to renal insufficiency.     

遗传性肾炎一家系COL4A5基因微卫星遗传标记单倍体图研究

目的 通过分析COL4A5基因附近的12个微卫星遗传标记形成的单倍体图，排除性定位一个Alpon综合征家系的致病相关基因。方法应用聚合酶链反应(PCR)扩增COL4A5基因附近的微卫星遗传标记DXS993、DXS991、DXS986、DXS990、DXS1106、DXS8048、DXSl220、DXS8055、DXS1001、DXS1047、DXS122、DXS8043，绘制单倍体图分析。结果该家族中来自不同家庭的患者COL4A5基因的微卫星标记单倍体型不同，并在遗传过程中在不同个体的COL4A5基因附近发生了交换。结论排除该Alport综合征家系致病基因是通过X染色体连锁的方式遗传，而可能是常染色体上基因突变致病。     

性连锁Alport综合征COL4A5基因突变检测

目的 检测16个家系20例性连锁Alport综合征患者COL4A4基因突变。方法：采用PCR－变性凝胶梯度电泳（DGGE）－直接测序法检测患者COL4A5基因中30个外显子及其相邻内含子区域（外显子1－25，31，32，41，50，51），另选取100例政党人外周血DNA作为对照。结果 共发现4种突变，包括1种位于1号外显子的无义突变（266C→T谷氨酰胺22终止密码），1种位于31号外显子上的错义突变（2575G→T甘氨酸852缬氨酸），以及2种分别位于1，25号内含子区域的剪接突变（283＋1G→T，2150＋1G→T）。结论 COL4A5基因为性连锁Alport综合征的致病基因，突变类型多样，尚未发现热点突变。类似于外显子突变，内含子突变同样具有致病意义。患者临床症状典型，查阅基因库，此4种突变均为首次报道。     

Variants of Alport's syndrome

Variants of Alport's syndrome include mainly those associated with hereditary macrothrombocytopenia (and occasionally leukocyte inclusions) or with esophageal, tracheobronchial and genital leiomyomatosis. Within Alport's syndrome there appears to be no justification for differentiating those with nephritis and deafness from those with nephritis alone. However, in indirect immunofluorescence studies using the mouse monoclonal antibody, MCA-P1, which recognizes the glomerular basement membrane (GBM), reduced or absent binding was found in 20 of 42 cases of hereditary nephritis. Most of these showed typical ultrastructural GMB changes. These results suggest that there is probably a subset of patients characterized by typical GBM lesions and an absence, inaccessibility or abnormality of the GBM antigen recognized by MCA-P1.     

Genetics of Alport's syndrome

The pattern of inheritance in Alport's syndrome has been controversial for some time. Recent studies have clarified the mode of inheritance in this disease. Alport's syndrome is a heterogeneous disorder made up of a number of genetically distinct syndromes, with an autosomal dominant, an X-linked dominant and a rare autosomal recessive form. Clinical analysis shows that there are many distinct forms with or without nerve deafness, and with early or late occurrence of end-stage renal disease.     

Renal transplantation in Alport's syndrome

Nineteen patients (3 women and 16 men) with Alport's Syndrome and endstage renal failure received 23 allograft kidneys at two medical centers between 1972 and 1983. Ten patients had pretransplant splenectomies, and four patients had pretransplant thoracic duct drainage. After a mean follow-up time of 49 months, analysis revealed total allograft survival was 65 per cent at 1 year, 50 per cent at 2 years, and 57 per cent at 5 years. Pretransplant splenectomy resulted in 60 per cent allograft survival at 24 months mean follow-up. Pretransplant thoracic duct drainage resulted in 100 per cent allograft survival at 15.6 months mean follow-up. The overall allograft survival was greatest for three and four antigen-matched kidneys and for living related donor kidneys. Data indicated that 50 per cent of all allografts in men were functional at 50.8 months mean follow-up. All allografts in women were functional at 48.3 months mean follow-up. Three of four patients who expired had pretransplant splenectomies. From this study, the authors conclude that renal transplantation is the preferred method of treatment for patients with Alport's Syndrome.