Emerging perspectives on hereditary glomerulopathies in canines

Abstract

Familial glomerulopathies have been described in more than two dozen dog breeds. These canine spontaneous cases of glomerular disease are good models for their human counterparts. The dogs present clinically with protein-losing nephropathy and variable signs of hypertension, thromboembolic events, edema/effusions/nephrotic syndrome, or eventually with signs of renal disease such as anorexia, vomiting, weight loss, and/or polyuria/polydipsia. Laboratory changes include proteinuria, hypoalbuminemia, hypercholesterolemia, and eventu- ally azotemia, hyperphosphatemia, anemia, and isosthenuria. Renal biopsies examined with transmission electron microscopy, immunofluorescence, and thin section light microscopy may show ultrastructural glomerular basement membrane abnormalities, glomerulosclerosis, amyloidosis, non-amyloid fibrillary deposition, or breed-associated predispositions for immune- complex glomerulonephritis. Genome-wide association studies and fine sequencing of candi - date genes have led to the discovery of variant alleles associated with disease in some breeds; eg, 1) glomerular basement membrane ultrastructural abnormalities due to defective collagen type IV, caused by different premature stop codons in each of four breeds; ie, in COL4A5 in Samoyeds and Navasota mix breed dogs (X-linked), and in COL4A4 in English Cocker Spaniels and English Springer Spaniels (autosomal recessive); and 2) glomerulosclerosis-related podo- cytopathy with slit diaphragm protein anomalies of both nephrin and Neph3/filtrin due to non- synonymous single nucleotide polymorphisms in conserved regions of their encoding genes, NPHS1 and KIRREL2, in Soft Coated Wheaten Terriers and Airedale Terriers, with a complex mode of inheritance. Age at onset and progression to end-stage renal disease vary depending on the model. Genetic counseling using DNA testing is available for several breeds but many more inherited canine models of glomerulopathy still need to be characterized. Dog breeds, with their long haplotypes and linkage disequilibrium, represent excellent models to study the underlying molecular basis for protein-losing nephropathy, glomerular function, genetic manipulations, possible environmental triggers, and treatments. Results of studies of genetic canine diseases will help dogs and other species, including man.