Characterization of the genetic basis for autosomal recessive hereditary nephropathy in the English Springer Spaniel

Incorporating Genetic Testing into a Breeding Program

Genetic tests are powerful tools that enable (1) a focus on genetic diversity as mating outcomes can be predicted and thus optimized to minimize or even avoid exclusion and (2) working toward breeding goals by improving a phenotype.

Bayesian mixed model analysis uncovered 21 risk loci for chronic kidney disease in boxer dogs

Chronic kidney disease (CKD) affects 10% of the human population, with only a small fraction genetically defined. CKD is also common in dogs and has been diagnosed in nearly all breeds, but its genetic basis remains unclear. Here, we performed a Bayesian mixed model genome-wide association analysis for canine CKD in a boxer population of 117 canine cases and 137 controls, and identified 21 genetic regions associated with the disease. At the top markers from each CKD region, the cases carried an average of 20.2 risk alleles, significantly higher than controls (15.6 risk alleles). An ANOVA test showed that the 21 CKD regions together explained 57% of CKD phenotypic variation in the population. Based on whole genome sequencing data of 20 boxers, we identified 5,206 variants in LD with the top 50 BayesR markers. Following comparative analysis with human regulatory data, 17 putative regulatory variants were identified and tested with electrophoretic mobility shift assays. In total four variants, three intronic variants from the MAGI2 and GALNT18 genes, and one variant in an intergenic region on chr28, showed alternative binding ability for the risk and protective alleles in kidney cell lines. Many genes from the 21 CKD regions, RELN, MAGI2, FGFR2 and others, have been implicated in human kidney development or disease. The results from this study provide new information that may enlighten the etiology of CKD in both dogs and humans.

Clinical and Histopathological Features of Renal Maldevelopment in Boxer Dogs: A Retrospective Case Series (1999-2018)

Simple Summary

This study describes clinical findings in Boxer dogs with renal maldevelopment and proposes a possible mode of inheritance. Medical records of 9 female Boxer dogs, older than 5 months and with a clinical diagnosis of proteinuric chronic kidney disease prior to one year of age, showed the presence of polyuria and polydipsia, decreased appetite, weight loss, lethargy and weakness in all affected dogs. Common laboratory findings were proteinuria and diluted urine, non-regenerative anemia, azotemia, hyperphosphatemia, hypoalbuminemia and hypercholesterolemia. Histopathology of the kidneys identified the presence of immature glomeruli in all dogs. In 7 out of 9 related dogs, the pedigree analysis showed that a simple autosomal recessive trait may be a possible mode of inheritance. Renal glomerular immaturity should be suspected in Boxer dogs with a history of polyuria, polydipsia, decreased appetite, weight loss, lethargy, weakness and proteinuria. A prompt diagnosis of renal maldevelopment, potentially hereditary, may help to evaluate if relatives of the affected dogs might be at risk, thus assisting clinicians in reaching an early diagnosis. A routine clinical renal screening evaluation in this breed, especially when this disease is suspected, should be strongly recommended.

Abstract

Renal maldevelopment (RM) has been proposed to replace the old and sometimes misused term “renal dysplasia” in dogs. Although renal dysplasia has been described in Boxers, hereditary transmission has only been hypothesized. This study reports clinical and renal histological findings in Boxer dogs with RM, proposing a possible mode of inheritance. Medical records of 9 female Boxer dogs, older than 5 months and with a clinical diagnosis of chronic kidney disease prior to one year of age, were retrospectively reviewed. Polyuria and polydipsia (PU/PD), decreased appetite, weight loss, lethargy and weakness were described in all affected dogs. Common laboratory findings were proteinuria, diluted urine, non-regenerative anemia, azotemia, hyperphosphatemia, hypoalbuminemia and hypercholesterolemia. Histopathology of the kidneys revealed the presence of immature glomeruli in all dogs, which is consistent with RM. In 7 related dogs, the pedigree analysis showed that a simple autosomal recessive trait may be a possible mode of inheritance. Renal maldevelopment should be suspected in young Boxer dogs with a history of PU/PD, decreased appetite, weight loss, lethargy, weakness and proteinuria. Due to its possible inheritance, an early diagnosis of RM may allow clinicians to promptly identify other potentially affected dogs among the relatives of the diagnosed case.

Pathological features of proteinuric nephropathy resembling Alport syndrome in a young Pyrenean Mountain dog

The renal biopsy tissue from a 9-month-old, male Pyrenean Mountain dog with renal disorder and severe proteinuria was examined. Ultrastructural examination revealed multilaminar splitting and fragmentation of the glomerular basement membrane (GBM) and diffuse podocyte foot process effacement. Immunofluorescent staining for α(IV) chains revealed presence of α5(IV) and complete absence of α3(IV) and α4(IV) chains in the GBM. Immunohistochemistry also revealed decreased and altered expression of nephrin and podocin in the glomeruli compared with normal canine glomeruli. These results suggested that the glomerular disease of the present case might be consistent with canine hereditary nephropathy resembling human Alport syndrome caused by genetic defect of type IV collagen, and indicated possible contribution of podocyte injury to severe proteinuria in this case.

Glomerulopathy and mutations in NPHS1 and KIRREL2 in soft-coated Wheaten Terrier dogs

Dogs of the soft-coated wheaten terrier breed (SCWT) are predisposed to adult-onset, genetically complex, protein-losing nephropathy (average onset age = 6.3 ± 2.0 years). A genome-wide association study using 62 dogs revealed a chromosomal region containing three statistically significant SNPs (p(raw) ≤ 4.13 × 10(-8); p(genome) ≤ 0.005) when comparing DNA samples from affected and geriatric (≥14 years) unaffected SCWTs. Sequencing of candidate genes in the region revealed single nucleotide changes in each of two closely linked genes, NPHS1 and KIRREL2, which encode the slit diaphragm proteins nephrin and Neph3/filtrin, respectively. In humans, mutations in nephrin and decreased expression of Neph3 are associated with podocytopathy and protein-losing nephropathy. The base substitutions change a glycine to arginine in the fibronectin type 3 domain of nephrin and a proline to arginine in a conserved proline-rich region in Neph3. These novel mutations are not described in other species, nor were they found in 550 dogs of 105 other breeds, except in 3 dogs, including an affected Airedale terrier, homozygous for both substitutions. Risk for nephropathy is highest in dogs homozygous for the mutations (OR = 9.06; 95 % CI = 4.24-19.35). This is the first molecular characterization of an inherited podocytopathy in dogs and may serve as a model for continued studies of complex genetic and environmental interactions in glomerular disease.