Mutation in the alpha 5(IV) collagen chain in juvenile-onset Alport syndrome without hearing loss or ocular lesions: detection by denaturing gradient gel electrophoresis of a PCR product.

A single base mutation was identified in the type IV collagen alpha 5 chain gene (COL4A5) of a Danish kindred with Alport syndrome. The 27-year-old male proband developed hematuria in childhood and terminal renal failure at the age of 25 years. He has no hearing loss or ocular lesions. Electron microscopy demonstrated splitting of the lamina densa of the glomerular basement membrane. The proband's mother has had persistent microscopic hematuria since the age of 40 years, but no other manifestations. Southern analysis of MspI-digested genomic DNA from the proband showed the absence of 1.3-kb and 0.9-kb fragments present in control DNA but the presence of a 2.2-kb variant fragment, indicating the loss of an MspI restriction site in the 3' end of the gene. The mother had all three fragments, indicating heterozygosity. PCR amplification of exon 14 (counted from the 3' end) and subsequent denaturing gradient gel electrophoresis analysis suggested a sequence variant in the proband and his mother. This was confirmed by sequencing of the PCR-amplified exon 14 region of the hemizygous proband, which demonstrated the base change G----A abolishing an MspI restriction site. Hybridization analysis with allele-specific probes confirmed the inheritance of the mutation with the phenotype. The mutation changed the GGC codon for glycine-1143 to GAC for aspartate. Substitution of glycine-1143, located in the collagenous domain of the alpha 5(IV) chain, for any other amino acid can be expected to interfere with the maintenance of the triple-helical conformation of the collagen molecule. This could, in turn, weaken the glomerular-basement-membrane framework and lead to increased permeability.