Objective—To assess heritability and mode of inheritance
for hypoadrenocorticism in Bearded Collies.
Animals—635 Bearded Collies.
Procedure—Dogs were classified as affected by
hypoadrenocorticism or unaffected. Phenotypic and
pedigree data were analyzed. Heritability was estimated
by use of Bayesian statistical methods.
Regressive logistic models for complex segregation
analyses were used to characterize mode of inheritance.
Results—Hypoadrenocorticism was diagnosed in
60 (9.4%) dogs. Heritability of hypoadrenocorticism
was estimated to be 0.76 with both sexes
affected with equal probability. Evaluation of the
pedigrees did not support a Mendelian autosomal
dominant mode of inheritance. Evidence from the
complex segregation analysis for a single locus of
large effect on hypoadrenocorticism was not convincing.
Conclusions and Clinical Relevance—Hypoadrenocorticism
in Bearded Collies is highly heritable.
Although a precise genetic mechanism responsible
for inheritance of the disorder remains undetermined,
breeding decisions must include consideration of the
genetic likelihood of passing on this deleterious disorder
to offspring of affected dams and sires. (Am J
Vet Res 2002;63:643–647).
Objective—To characterize heritability and mode of inheritance of cataracts and primary lens luxation in Jack Russell Terriers.
Animals—872 Jack Russell Terriers from which buccal epithelial cells were collected and phenotypes for cataracts and lens luxation were determined and an additional 1,898 Jack Russell Terriers without phenotypic information used to complete pedigree relationships and that were included in the analyses.
Procedures—Narrow-sense heritabilities and genetic correlation for cataracts and lens luxation were modeled by use of threshold analysis, whereas complex segregation analysis was used to characterize mode of inheritance. For the analyses, dogs < 6 years old, unless confirmed as having cataracts or lens luxation, were classified as an unknown phenotype. The possible involvement of an HSF4 mutation in cataracts was determined by DNA sequencing.
Results—Cataracts and primary lens luxation were highly heritable and genetically correlated, and neither was controlled by a single gene. Cataracts were not associated with an HSF4 mutation.
Conclusions and Clinical Relevance—Analysis of the data indicated that concerted selection against both cataracts and primary lens luxation when choosing breeding animals can be used to improve ocular health in Jack Russell Terriers.
Objective—To determine the proportion of mixed-breed and purebred dogs with common genetic disorders.
Animals—27,254 dogs with an inherited disorder.
Procedures—Electronic medical records were reviewed for 24 genetic disorders: hemangiosarcoma, lymphoma, mast cell tumor, osteosarcoma, aortic stenosis, dilated cardiomyopathy, hypertrophic cardiomyopathy, mitral valve dysplasia, patent ductus arteriosus, ventricular septal defect, hyperadrenocorticism, hypoadrenocorticism, hypothyroidism, elbow dysplasia, hip dysplasia, intervertebral disk disease, patellar luxation, ruptured cranial cruciate ligament, atopy or allergic dermatitis, bloat, cataracts, epilepsy, lens luxation, and portosystemic shunt. For each disorder, healthy controls matched for age, body weight, and sex to each affected dog were identified.
Results—Genetic disorders differed in expression. No differences in expression of 13 genetic disorders were detected between purebred dogs and mixed-breed dogs (ie, hip dysplasia, hypo- and hyperadrenocorticism, cancers, lens luxation, and patellar luxation). Purebred dogs were more likely to have 10 genetic disorders, including dilated cardiomyopathy, elbow dysplasia, cataracts, and hypothyroidism. Mixed-breed dogs had a greater probability of ruptured cranial cruciate ligament.
Conclusions and Clinical Relevance—Prevalence of genetic disorders in both populations was related to the specific disorder. Recently derived breeds or those from similar lineages appeared to be more susceptible to certain disorders that affect all closely related purebred dogs, whereas disorders with equal prevalence in the 2 populations suggested that those disorders represented more ancient mutations that are widely spread through the dog population. Results provided insight on how breeding practices may reduce prevalence of a disorder.