Canine X chromosome-linked hereditary nephritis: a genetic model for human X-linked hereditary nephritis resulting from a single base mutation in the gene encoding the alpha 5 chain of collagen type IV.

Many families with X-chromosome linked hereditary nephritis (HN) have mutations in the gene on the X chromosome that codes for the alpha 5 chain of collagen type IV. Canine X-linked HN is an animal model for human X-linked HN. To study the alpha 5(IV) gene in this model, we used the nucleotide sequence published for the human alpha 5(IV) cDNA to construct sets of primers covering approximately 95% of the complete cDNA. cDNA from both affected and normal dog kidneys was amplified by PCR in nine overlapping regions. The nucleotide sequence encoding the noncollagenous domain NC1 hybridized to the human X chromosome and was 93% identical at the DNA level and 97% identical at the protein level to the human alpha 5(IV) NC1 domain, confirming that the canine alpha 5(IV) cDNA had been amplified. Sequence analysis of the alpha 5(IV) cDNA detected a single nucleotide substitution, G-->T, in affected dogs, changing a codon for a conserved glycine residue (GGA) to a stop codon (TGA). When genomic DNA was amplified, the same abnormality was found in exon 35. Using the canine NC1 domain cDNA as a probe for Northern analysis, two transcripts of approximately 8.6 kb and approximately 6.7 kb were identified in both normal and affected male dog kidney RNA. However, the abundance of both transcripts was decreased by a factor of approximately 10 in the affected dog. These results establish at the molecular level that canine X-linked HN is a model for human X-linked HN. This model provides an opportunity to determine the efficacy of new therapies and to investigate the role of the alpha 5(IV) chain in type IV collagen assembly.