Presence and impact of the exercise-induced collapse associated DNM1 mutation in Labrador retrievers and other breeds

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.

Heritability and Genomic Architecture of Episodic Exercise-Induced Collapse in Border Collies

An episodic nervous system disorder triggered by strenuous exercise, termed border collie collapse (BCC), exists in border collies and related breeds. The genetic basis of BCC is unknown but is believed to be a complex genetic disorder. Our goal was to estimate the heritability (h²_SNP) of BCC, define its underlying genetic architecture, and identify associated genomic loci using dense whole-genome single-nucleotide polymorphism (SNP) genotyping data. Genotype data were obtained for ~440,000 SNPs from 343 border collies (168 BCC cases and 175 controls). h²_SNP was calculated to be 49–61% depending on the estimated BCC prevalence. A total of 2407 SNPs across the genome accounted for nearly all the h2_SNP of BCC, with an estimated 2003 SNPs of small effect, 349 SNPs of moderate effect, and 56 SNPs of large effect. Genome-wide association analyses identified significantly associated loci on chromosomes 1, 6, 11, 20, and 28, which accounted for ~5% of the total BCC h²_SNP. We conclude that BCC is a moderately- to highly-heritable complex polygenetic disease resulting from contributions from hundreds to thousands of genetic variants with variable effect sizes. Understanding how much the BCC phenotype is determined by genetics and whether major gene mutations are likely to exist inform veterinarians and working/stock dog communities of the true nature of this condition.

Web resource on available DNA variant tests for hereditary diseases and genetic predispositions in dogs and cats: An Update

Vast progress has been made in the clinical diagnosis and molecular basis of hereditary diseases and genetic predisposition in companion animals. The purpose of this report is to provide an update on the availability of DNA testing for hereditary diseases and genetic predispositions in dogs and cats utilizing the WSAVA-PennGen DNA Testing Database web resource (URL: http://research.vet.upenn.edu/WSAVA-LabSearch ). Information on hereditary diseases, DNA tests, genetic testing laboratories and afflicted breeds added to the web-based WSAVA-PennGen DNA Testing Database was gathered. Following verification through original research and clinical studies, searching various databases on hereditary diseases in dogs and cats, and contacting laboratories offering DNA tests, the data were compared to the resource reported on in 2013. The number of molecularly defined Mendelian inherited diseases and variants in companion animals listed in the WSAVA-PennGen DNA Testing Database in 2020 drastically increased by 112% and 141%, respectively. The number of DNA variant tests offered by each laboratory has also doubled for dogs and cats. While the overall number of laboratories has only slightly increased from 43 to 47, the number of larger corporate laboratories increased, while academic laboratories have declined. In addition, there are now several laboratories that are offering breed-specific or all-breed panel tests rather than single-DNA tests for dogs and cats. This unique regularly updated searchable web-based database allows veterinary clinicians, breeders and pet owners to readily find available DNA tests, laboratories performing these DNA tests worldwide, and canine and feline breeds afflicted and also serves as a valuable resource for comparative geneticists.

DNM1 mutation status, sex, and sterilization status of a cohort of Labrador retrievers with and without cranial cruciate ligament rupture

Background

Exercise-induced collapse (EIC) due to DNM1 mutation and rupture of the cranial cruciate ligament are both common syndromes in the Labrador retriever breed. A cohort of 313 Labradors was recruited based on their CCLR status and were subsequently genetically tested for EIC. Epidemiological aspects of the cohort were also described, including sex, sterilization status, and age at sterilization.

Results

No sex difference was observed in dogs susceptible to EIC (homozygous for the mutant genotype) compared to dogs not susceptible to EIC (heterozygotes and dogs homozygous for the normal genotype). No evidence for association was detected between CCLR status and EIC status (p =0.357), although the sample cohort was not of sufficient size to entirely rule out an association. A significant difference (p = 0.031) was observed in the sex distribution of dogs affected with CCLR compared to those without CCLR. An increased number of female CCLR cases were observed compared to the number of female controls; male CCLR cases and controls were approximately the same number. When CCLR status was examined in each sex, no significant differences were observed between those that were sterilized and those that weren’t. However, for female dogs that were sterilized, CCLR cases were significantly higher in dogs sterilized at one year of age or younger compared to those sterilized when over the age of one year (p = 0.0021, OR 4.30, 95% CI 1.55–12.72); for males, this finding was suggestive, but not statistically significant (p = 0.0913, OR 3.57, 95% CI 0.809–14.476).

Conclusions

CCLR is not associated with a large increase in EIC occurrence. Statistically, these two syndromes cannot be proven to be unrelated; however, concomitant occurrence of CCLR and EIC in Labrador retrievers is rare, despite the high prevalence of both syndromes in this breed. Epidemiological findings suggest that females may be over-represented in CCLR cases and that early sterilization (≤1 year) may increase the risk of Labradors developing CCLR later in life (particularly in females). These results should be considered preliminary and require confirmation in larger populations of Labrador retrievers.

Border Collie Collapse: Owner Survey Results and Veterinary Description of Videotaped Episodes

Completed surveys were obtained from owners of 165 border collies experiencing repeated episodes of abnormal gait or collapse during strenuous exercise. Unremarkable veterinary evaluation and lack of disease progression over time made common systemic, cardiac, and neurologic causes of exercise intolerance unlikely. Survey questions addressed signalment, age of onset, description of episodes, and owner perception of factors associated with collapse. Most dogs were young adults (median 2 yr) when episodes began, and they had experienced from 2 to more than 100 episodes (median 6) prior to their owners completing the survey. Retrieving was the activity most commonly associated with episodes (112/165 dogs, 68%), followed by herding stock (39/165 dogs, 24%). Owners reported that high environmental temperatures (111/165 dogs, 67%) and excitement (67/165 dogs, 41%) increased the likelihood of their dog having an episode during strenuous activity. Veterinary evaluation of videotapes of presumed border collie collapse (BCC) episodes (40 dogs) were used to provide a description of the typical features of BCC episodes. Altered mentation, symmetrical ataxia affecting all four limbs, increased pelvic limb extensor tone and toe scuffing or knuckling, truncal swaying, and falling to the side were common features, suggesting that BCC may be an episodic diffuse central nervous system disorder.

Toward the most ideal case-control design with related and unrelated dogs in whole-exome sequencing studies

With the recent development of whole-exome sequencing enrichment designs for the dog, a novel tool for disease-association studies became available. The aim of disease-association studies is to identify one or a very limited number of putative causal variants or genes from the large pool of genetic variation. To maximize the efficiency of these studies and to provide some directions of what to expect, we evaluated the effect on variant reduction for various combinations of cases and controls for both dominant and recessive types of inheritance assuming variable degrees of penetrance and detectance. In this study, variant data of 14 dogs (13 Labrador Retrievers and one Dogue de Bordeaux), obtained by whole-exome sequencing, were analyzed. In the filtering process, we found that unrelated dogs from the same breed share up to 70% of their variants, which is likely a consequence of the breeding history of the dog. For the designs tested with unrelated dogs, combining two cases and two controls gave the best result. These results were improved further by adding closely related dogs. Reduced penetrance and/or detectance has a drastic effect on the efficiency and is likely to have a profound effect on the sample size needed to elucidate the causal variant. Overall, we demonstrated that sequencing a small number of dogs results in a marked reduction of variants that are likely sufficient to pinpoint causal variants or genes.

International Veterinary Epilepsy Task Force's current understanding of idiopathic epilepsy of genetic or suspected genetic origin in purebred dogs

Canine idiopathic epilepsy is a common neurological disease affecting both purebred and crossbred dogs. Various breed-specific cohort, epidemiological and genetic studies have been conducted to date, which all improved our knowledge and general understanding of canine idiopathic epilepsy, and in particular our knowledge of those breeds studied. However, these studies also frequently revealed differences between the investigated breeds with respect to clinical features, inheritance and prevalence rates. Awareness and observation of breed-specific differences is important for successful management of the dog with epilepsy in everyday clinical practice and furthermore may promote canine epilepsy research. The following manuscript reviews the evidence available for breeds which have been identified as being predisposed to idiopathic epilepsy with a proven or suspected genetic background, and highlights different breed specific clinical features (e.g. age at onset, sex, seizure type), treatment response, prevalence rates and proposed inheritance reported in the literature. In addition, certain breed-specific diseases that may act as potential differentials for idiopathic epilepsy are highlighted.

The prevalence of nine genetic disorders in a dog population from Belgium, the Netherlands and Germany

The objective of this study was to screen a dog population from Belgium, the Netherlands and Germany for the presence of mutant alleles associated with hip dysplasia (HD), degenerative myelopathy (DM), exercise-induced collapse (EIC), neuronal ceroid lipofuscinosis 4A (NCL), centronuclear myopathy (HMLR), mucopolysaccharidosis VII (MPS VII), myotonia congenita (MG), gangliosidosis (GM1) and muscular dystrophy (Duchenne type) (GRMD). Blood samples (K3EDTA) were collected for genotyping with Kompetitive Allele Specific PCR (n = 476). Allele and genotype frequencies were calculated in those breeds with at least 12 samples (n = 8). Hardy-Weinberg equilibrium was tested. Genetic variation was identified for 4 out of 9 disorders: mutant alleles were found in 49, 15, 3 and 2 breeds for HD, DM, EIC and NCL respectively. Additionally, mutant alleles were identified in crossbreeds for both HD and EIC. For HD, DM, EIC and NCL mutant alleles were newly discovered in 43, 13, 2 and 1 breed(s), respectively. In 9, 2 and 1 breed(s) for DM, EIC and NCL respectively, the mutant allele was detected, but the respective disorder has not been reported in those breeds. For 5 disorders (HMLR, MPS VII, MG, GM1, GRMD), the mutant allele could not be identified in our population. For the other 4 disorders (HD, DM, EIC, NCL), prevalence of associated mutant alleles seems strongly breed dependent. Surprisingly, mutant alleles were found in many breeds where the disorder has not been reported to date.

Genotyping of exercise-induced collapse in Labrador retrievers using an allele-specific PCR

Exercise-induced collapse (EIC) is an autosomal recessive disorder in Labrador retrievers. In this study, an allele-specific PCR was developed to detect the point mutation G767T in exon 6 of canine DNM1, previously shown to be responsible for canine EIC. Of 133 Labrador retrievers tested in Japan, 6 (4.5%) were homozygous (EIC) and 50 (37.6%) were heterozygous (carriers) for the G767T mutation.