The COL4A5 gene in Japanese Alport syndrome patients: Spectrum of mutations of all exons

Abstract

To determine the spectrum of mutations of the COL4A5 gene encoding type IV collagen among Japanese Alport syndrome (AS) patients, 60 unrelated patients (47 males and 13 females) from all over the country were recruited. Screening for mutations in all the exons (1 to 51) of the COL4A5 gene was carried out by PCR-SSCP analysis. A mobility shift was observed in 22 of 60 patients, and their genomic DNA were analyzed by the direct sequence method and using cloned ssDNA. Nine of these had missense mutations in the collagenous domain (in exons 39, 37, 31, 29, 28, 27, 21, 20, 19). Eight of these mutations were observed in a codon of glycine residue. Two were altered to arginine, two to valine, two to glutamic acid and two to aspartic acid. The other missense mutation was a change from isoleucine to serine in a interruption region. Five patients had small size base deletions and one had a 4 bp insertion resulting in frameshift (in exons 49, 41, 19, 14, 13). Three had a splice site mutation (in exons 49, 47, 27). One had a nonsense mutation (in exon 17). These mutations seemed to be pathogenic, but the phenotype, which includes extrarenal manifestations, can vary with respect to both expression and severity. The remaining mutations were three silent ones (in exons 19, 39, 46). In addition, major gene rearrangement seemed to be rare in Japanese AS patients.

Glomerular Expression of Type IV Collagen Chains in Normal and X-Linked Alport Syndrome Kidneys

“…6 -11 COL4A5 mutations lead to the most common form of AS which is X-linked, whereas COL4A3 and COL4A4 mutations are responsible for the autosomal recessive forms. [12][13][14][15][16][17][18][19] The primary structure of the six ␣(IV) chains is very similar. Each is characterized by an ϳ25-residue noncollagenous domain at the amino terminus, an ϳ1400 residue collagenous domain of Gly-X-Y repeats (in which X is frequently proline and Y is frequently hydroxyproline), that forms, in association with two other chains, the triple helix, and an ϳ230-residue noncollagenous (NC1) domain at the carboxyl terminus.…”

“…28 -31 The presence of cysteine-rich ␣3(IV) and ␣4(IV) chains, forming with ␣5(IV) a network containing loops and supercoiled triple helices stabilized by disulfide bonds between the chains, seems to be important with regards to the longterm stability of the GBM and its role as a filter. 26,32 Despite the increasing number of AS mutations reported in the literature [12][13][14][15][16][17][18][19] and the existence of AS animal models, [33][34][35][36][37] several questions regarding the consequences of AS mutations on the collagen organization within the GBM and the mechanisms responsible for the progressive development of AS nephropathy remain unanswered. A striking feature observed in the majority of AS is the absence of all three ␣3(IV), ␣4(IV), and ␣5(IV) chains within the GBM although only one of these chains is actually mutated.…”

A New Point Mutation in the COL4A5 Gene Described in a Spanish Family with X-Linked Alport Syndrome

“…The COL4A5 is a large gene, with 51 exons and a length of 250 kb [21], that produces a 6.5-kb mRNA. The big size of this gene complicates its study, especially when no hot spots have been described, so all described mutations (nearly 300) [22]are spread all over the gene [23, 24, 25, 26, 27, 28]. Moreover, mutations cause a variety of phenotypes, and in the case of single-base mutations, it has been difficult to establish a correlation between the genotype and the phenotype [15, 29, 30], since similar mutations or mutations at similar positions can produce either a severe or a moderate phenotype.…”

Alport Syndrome with a Peculiar Pattern of Distribution of the α3–α6 Chains of Type IV Collagen in Renal Basement Membrane

“…In the majority or X-linked male AS, α3, α4, α5, and α6 type IV collagen (α3(IV)–α6(IV)) chains are absent or faint in the kidney [1]and variety of mutation have been reported in the COL4A5 [2]. Mutations in COL4A3 or COL4A4 have been identified [3]and the absence of the α3(IV)–α5(IV) chains in the glomerular basement membrane (BM) and the presence of the α5(IV) chain in extraglomerular BM in autosomal-recessive AS [4].…”

“…Creatinine clearance was 89.3 ml/min/1.73 m 2 . Screening analysis for mutation in each 5 exons of COL4A3 and COL4A4 [3], and all 51 exons of COL4A5 [2]was done by the single-strand conformation polymorphism (SSCP) method after amplification of each exon by the polymerase chain reaction (PCR) method (PCR-SSCP analysis) [2, 3]using peripheral leukocytes obtained from the patient, his sister, and his father, but not from his mother. PCR-SSCP analysis showed no abnormal shift on the gel electrophoresis.…”