Canine hereditary nephropathies : Molecular genetic studies in Norwegian Elkhounds and English Cocker Spaniels

Abstract

Hereditary nephropathies have been described in a variety of dog breeds. The causative mutation has been identified in a minority of canine renal diseases, and these provide useful animal models to study in order to gain knowledge on human nephropathies. In this thesis, canine hereditary nephropathies are investigated in the Norwegian Elkhound dog and the English Cocker Spaniel. A family of grey Norwegian Elkhound dogs with familial renal disease was phenotyped, including light microscopical, electron microscopical and immunofluorescence studies of kidney lesions. Based on laboratory parameters, renal clearance tests and examination of kidney tissue, diagnosis of familial renal disease in an early stage was difficult. Previously, the earliest lesions in kidneys were described to be periglomerular fibrosis. We identified even earlier lesions in our family, based on which we could redefine this disease as a glomerular problem rather than a tubulo-interstitial problem, as suggested earlier by others. The three generation family we followed in time was phenotyped to identify individuals that were with certainty affected. Based on the segregation pattern of the disease in the pedigree, an autosomal dominant mode of inheritance of familial renal disease seemed most likely. The cDNA sequence, genomic annotation and map position were determined for two canine collagen type IV genes, COL4A3 and COL4A4. These closely linked, neighboring genes were previously appointed as candidate genes for a number of canine hereditary nephropathies, based on histological similarities with human Alport syndrome. COL4A3 and COL4A4 were studied as candidate genes in familial renal disease in the Norwegian Elkhound dog, using a limited number of family based samples. Three closely linked polymorphic microsatellite markers were developed with help of a canine BAC library. The segregation pattern of familial renal disease was compared to the pattern of the COL4A3/COL4A4 genes, represented by the 3 microsatellites, in the Norwegian Elkhound dog family. The observation of one affected dog that did not share the haplotype-at-risk with other affected dogs, made involvement of these genes in familial renal disease unlikely. The involvement of COL4A3 and COL4A4 was also studied in hereditary nephropathy in English Cocker Spaniels, by means of SNPs. Newly developed COL4A3/COL4A4 SNPs were genotyped in samples of both young and elderly affected English Cocker Spaniels (≤ and > 24 months of age, respectively). A recently published causal nonsense mutation in COL4A4 was observed in all young affected dogs homozygously, but was not found in the older dogs, indicating the existence of a second type of renal disease in English Cocker Spaniels with the same histological picture. The genetic background of familial renal disease in Norwegian Elkhound dogs was investigated farther by means of a genome wide approach, using an extended pedigree. In a multipoint linkage analysis of the genotyping data of ~1500 SNPs with genome wide coverage, in which only the genotypes of affected dogs were considered, significant positive LOD scores were detected on CFA17. Two regions on this chromosome were studied by means of additional markers and in a larger sample set, including 2 small families from the Norwegian population. Linkage was confirmed with a LOD score > 3, mapping familial renal disease to a 10 Mb region of CFA17.