Genetic Panel Screening of Nearly 100 Mutations Reveals New Insights into the Breed Distribution of Risk Variants for Canine Hereditary Disorders

Abstract

Background: The growing number of identified genetic disease risk variants across dog breeds challenges the current state-of-the-art of population screening, veterinary molecular diagnostics, and genetic counseling. Multiplex screening of such variants is now technologically feasible, but its practical potential as a supportive tool for canine breeding, disease diagnostics, pet care, and genetics research is still unexplored.

Results: To demonstrate the utility of comprehensive genetic panel screening, we tested nearly 7000 dogs representing around 230 breeds for 93 disease-associated variants using a custom-designed genotyping microarray (the MyDogDNA® panel test). In addition to known breed disease-associated mutations, we discovered 15 risk variants in a total of 34 breeds in which their presence was previously undocumented. We followed up on seven of these genetic findings to demonstrate their clinical relevance. We report additional breeds harboring variants causing factor VII deficiency, hyperuricosuria, lens luxation, von Willebrand's disease, multifocal retinopathy, multidrug resistance, and rod-cone dysplasia. Moreover, we provide plausible molecular explanations for chondrodysplasia in the Chinook, cerebellar ataxia in the Norrbottenspitz, and familiar nephropathy in the Welsh Springer Spaniel.

Conclusions: These practical examples illustrate how genetic panel screening represents a comprehensive, efficient and powerful diagnostic and research discovery tool with a range of applications in veterinary care, disease research, and breeding. We conclude that several known disease alleles are more widespread across different breeds than previously recognized. However, careful follow up studies of any unexpected discoveries are essential to establish genotype-phenotype correlations, as is readiness to provide genetic counseling on their implications for the dog and its breed.

Fig 1. Coagulation factor VII deficiency in the Welsh Springer Spaniel.

(A) Prolonged prothrombin times (t(2) = 8.21, p = 0.007) but normal partial thromboplastin times (data not shown); and (B) low plasma factor VII activity (t(3) = 9.17, p = 0.001) indicate functional factor VII deficiency and increased bleeding tendency in Welsh Springer Spaniels homozygous for the F7 gene c.407G>A missense variant. (** P < 0.01).

Fig 2. Hyperuricosuria in the Lagotto Romagnolo.

Elevated urine uric acid/creatinine ratios (F(2,11) = 85.9, p = 1.93x10^-7) in Lagotti homozygous for the SLC2A9 gene c.616G>T variant indicate metabolic derangement and predisposition to urate stone formation. (*** P < 0.001; n.s. = not significant)

Fig 3. Inheritance of cerebellar ataxia in a pedigree of Norrbottenspitzes.

All Norrbottenspitzes identified as carrying the Finnish Hound ataxia mutation (SEL1L c.1972T>C) can be traced back to the oldest obligate carrier dog (marked with an arrow symbol). Three dogs of unconfirmed background (squared on gray background) registered into the breed represent potential events of introduction of the mutation into the Norrbottenspitz populaation. A puppy (squared on white background) euthanized due to neurological symptoms matching the expected disease phenotype was born from a mating between two carrier dogs. Gender symbols of dogs with unconfirmed genotypes are shaded gray.

Fig 4. Chondrodysplasia in the Chinook.

(A) Inheritance of chondrodysplasia in a pedigree of Chinooks. All carriers of the responsible variant (ITGA10 c.2083C>T), and a genetically affected dog (squared) confirmed to have a dwarf phenotype are related to the first dwarves documented in the 1990’s as a result of a brother-sister mating (marked with an x). The mutation was likely propagated in the population through the sire of that mating (marked with an arrow), who was further bred to several other females. Gender symbols of dogs with unconfirmed genotypes are shaded gray. (B) A Chinook displaying the dwarfism phenotype (left; and squared in the pedigree) with crooked and shortened legs is shown in comparison to a normal Chinook (right).