A nonsense mutation in the COL4A5 collagen gene in a family with X-linked juvenile Alport syndrome

Mutation detection of COL4An gene based on mRNA of peripheral blood lymphocytes and prenatal diagnosis of Alport syndrome in China

AIM

Alport syndrome (AS) is a progressive renal disease characterized by haematuria and progressive renal failure. An accurate genetic diagnosis of AS is very important for genetic counselling and even prenatal diagnosis.

METHODS

We detected mutation of COL4An by amplifying the entire coding sequence mRNA of peripheral blood lymphocytes using polymerase chain reaction (PCR) in five Chinese AS families who asked for genetic counselling and prenatal diagnosis, then performed prenatal genetic diagnosis for four families. Mutation analysis of the foetus was made using DNA extracted from amniocytes. Foetus sex was determined by PCR amplification of SRY as well as karyotype analysis. Maternal cell contamination was excluded by linkage analysis.

RESULTS

Four different COL4A5 gene variants and two COL4A3 gene variants were detected in the five families. Because there was a de novo mutation in family 2, prenatal diagnosis was performed for the other four families. Results showed a normal male foetus for family 1 and family 4, respectively. Results showed an affected male foetus for families 3 and 5, and the pregnancies were terminated.

CONCLUSION

An easier, faster and efficacious method for COL4An gene mutation screening based on mRNA analysis from peripheral blood lymphocytes was established. Prenatal genetic diagnosis was performed in four AS families in China.

Prenatal diagnosis and genetic counseling of a Chinese Alport syndrome kindred

Alport syndrome (AS) is a progressive renal disease characterized by hematuria and progressive renal failure. X-linked dominant AS (XLAS) is the major inheritance form, accounting for almost 80% of the cases, caused by mutations in COL4A5 gene. An accurate genetic diagnosis of AS is very important for genetic counseling and even prenatal diagnosis. In this study we detected mutation of COL4A5 by amplifying the entire coding sequence mRNA of peripheral blood lymphocytes using nested PCR in a Chinese XLAS family, and then performed the first prenatal diagnosis of AS in China. Mutation analysis of the fetus was performed on both cDNA-based level and DNA-based level of amniocytes. Fetus sex was determined by PCR amplification of SRY and karyotypes analysis. Maternal cell contamination was excluded by linkage analysis. There was a G-to-A substitution at position 4,271 in exon 46 of COL4A5 gene (c.G4271A) in the pregnant woman; this genetic variant has not been described previously and was a novel missense mutation. The fetus did not carry the same mutation as the mother. PCR amplification product of SRY and karyotypes analysis revealed a male fetus. Linkage analysis showed that there was no contamination of maternal cells in amniocytes.

Detection of mutations in the COL4A5 gene by SSCP in X-linked Alport syndrome

Alport syndrome is a progressive renal disease leading to chronic renal failure, which often is accompanied by sensorineural deafness and ophthalmological signs in the form of anterior lenticonus. The X-linked form of the disease is caused by mutations in the COL4A5 gene encoding the alpha5-chain of type IV-collagen. We performed mutation analysis of the COL4A5 gene by PCR-SSCP analysis of each of the 51 exons with flanking intronic sequences in 81 patients suspected of X-linked Alport syndrome including 29 clear X-linked cases, 37 cases from families with a pedigree compatible with X-linked inheritance, and 15 isolated cases. We found a mutation detection rate of 52% (42/81) (58% in males and 21% in females), and 69% (20/29) in families who clearly demonstrated X-linked inheritance. Thirty-six different mutations were found in 42 patients comprising 16 missense mutations, seven frameshifts, three in-frame deletions, four nonsense mutations, and six splice site mutations. Twenty-two of the mutations have not previously been reported. Furthermore, we found one non-pathogenic amino acid substitution, one rare variant in a non-coding region, and one polymorphism with a heterozygosity of 28%. Three de novo mutations were found, two of which were paternal and one of maternal origin.

The clinical spectrum of type IV collagen mutations

Clinical manifestations of type IV collagen mutations can vary from the severe, clinically and genetically heterogeneous renal disorder, Alport syndrome, to autosomal dominant familial benign hematuria. The predominant form of Alport syndrome is X-linked; more than 160 different mutations have yet been identified in the type IV collagen alpha 5 chain (COL4A5) gene, located at Xq22-24 head to head to the COL4A6 gene. The autosomal recessive form of Alport syndrome is caused by mutations in the COL4A3 and COL4A4 genes, located at 2q35-37. Recently, the first mutation in the COL4A4 gene was identified in familial benign hematuria. This paper presents an overview of type IV collagen mutations, including eight novel COL4A5 mutations from our own group in patients with Alport syndrome. The spectrum of mutations is broad and provides insight into the clinical heterogeneity of Alport syndrome with respect to age at renal failure and accompanying features such as deafness, leiomyomatosis, and anti-GBM nephritis.

Alport syndrome. An inherited disorder of renal, ocular, and cochlear basement membranes

Alport syndrome (AS) is a genetically heterogeneous disease arising from mutations in genes coding for basement membrane type IV collagen. About 80% of AS is X-linked, due to mutations in COL4A5, the gene encoding the alpha 5 chain of type IV collagen (alpha 5[IV]). A subtype of X-linked Alport syndrome (XLAS) in which diffuse leiomyomatosis is an associated feature reflects deletion mutations involving the adjacent COL4A5 and COL4A6 genes. Most other patients have autosomal recessive Alport syndrome (ARAS) due to mutations in COL4A3 or COL4A4, which encode the alpha 3(IV) and alpha 4(IV) chains, respectively. Autosomal dominant AS has been mapped to chromosome 2 in the region of COL4A3 and COL4A4. The features of AS reflect derangements of basement membrane structure and function resulting from changes in type IV collagen expression. The primary pathologic event appears to be the loss from basement membranes of a type IV collagen network composed of alpha 3, alpha 4, and alpha 5(IV) chains. While this network is not critical for normal glomerulogenesis, its absence appears to provoke the overexpression of other extracellular matrix proteins, such as the alpha 1 and alpha 2(IV) chains, in glomerular basement membranes, leading to glomerulosclerosis. The diagnosis of AS still relies heavily on histologic studies, although routine application of molecular genetic diagnosis will probably be available in the future. Absence of epidermal basement membrane expression of alpha 5(IV) is diagnostic of XLAS, so in some cases kidney biopsy may not be necessary for diagnosis. Analysis of renal expression of alpha 3(IV)-alpha 5(IV) chains may be a useful adjunct to routine renal biopsy studies, especially when ultrastructural changes in the GBM are ambiguous. There are no specific therapies for AS. Spontaneous and engineered animal models are being used to study genetic and pharmacologic therapies. Renal transplantation for AS is usually very successful. Occasional patients develop anti-GBM nephritis of the allograft, almost always resulting in graft loss.

First Open-Heart Surgery in Alport Syndrome

We report the first case of open-heart surgery in a patient with Alport syndrome, which refers to the clinical triad of hereditary nephritis, sensory neural deafness, and ocular abnormalities. The conduct of cardiopulmonary bypass, the bleeding tendency, and the precautions taken in a patient with end-stage renal failure are discussed.

Rapid DNA-based prenatal diagnosis by genetic linkage in three families with Alport's syndrome

Alport's syndrome (AS) is a clinically and genetically heterogeneous progressive inherited glomerulonephritis characterized by hematuria, sensorineural hearing loss, ocular lesions, and specific alterations of the glomerular basement membrane. Typically, AS shows an X-linked dominant pattern of inheritance, with mutations affecting the collagen type IV alpha5 chain gene (COL4A5) at Xq22. Rarely, AS is caused in some families by mutations of the COL4A3/A4 genes on chromosome 2q, showing an autosomal recessive transmission. Very few families have been described with possible autosomal dominant AS, but no mutations in any of the COL4 genes have been found. We describe three unrelated families affected with a severe AS phenotype in which DNA-based prenatal diagnosis by linkage analysis was made in fetuses at risk for the disease. In two families, the pedigree structure and the clinical picture were consistent with typical X-linked dominant AS. In these families, autosomal inheritance was also ruled out molecularly. In one family, despite careful clinical and molecular evaluation, the mode of transmission could not be firmly established. We used tightly linked and intragenic COL4A5 markers, as well as COL4A3/A4-linked markers. A chromosome Y-specific marker for fetal sex determination was simultaneously used. In all the families, before the fetal analysis, the putative at-risk X haplotype was identified with high diagnostic accuracy. We diagnosed a healthy male fetus in one family, and female but carrier fetuses in the other two kindreds, who decided not to terminate their pregnancies. We used rapid nonisotopic polymerase chain reaction-based methods, and the results were available within 2 to 3 days. The genetic results significantly affected the reproductive decisions of the parents. This report illustrates the application of genetic linkage analysis as an additional tool for molecular diagnosis in AS, and also addresses the issue of the attitudes of the families toward prenatal testing. To our knowledge, prenatal diagnosis of AS using a genetic linkage approach has not been previously reported.