CANINE X-CHROMOSOME-LINKED HEREDITARY NEPHRITIS - A GENETIC MODEL FORHUMAN 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 c hain of collagen type IV. Canine X-linked HN is an animal model for hu man 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 co nstruct sets of primers covering approximate to 95% of the complete cD NA. cDNA from both affected and normal dog kidneys was amplified by PC R in nine overlapping regions. The nucleotide sequence encoding the no ncollagenous domain NC1 hybridized to the human X chromosome and was 9 3% identical at the DNA level and 97% identical at the protein level t o 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) cD NA detected a single nucleotide substitution, G --> T, in affected dog s, changing a codon for a conserved glycine residue (GGA) to a stop co don (TGA). When genomic DNA was amplified, the same abnormality was fo und in exon 35. Using the canine NC1 domain cDNA as a probe for Northe rn analysis, two transcripts of approximate to 8.6 kb and approximate to 6.7 kb were identified in both normal and affected male dog kidney RNA. However, the abundance of both transcripts was decreased by a fac tor of <a pproximate to> 10 in the affected dog. These results establi sh 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 effi cacy of new therapies and to investigate the role of the alpha 5(IV) c hain in type TV collagen assembly.