Abstract
Objective—To quantify inheritance of tricuspid valve dysplasia (TVD) in a population of Labrador Retrievers and evaluate the possibility of the effect of a major locus on TVD.
Animals—521 Labrador Retrievers (345 with known phenotypes and 176 related dogs with unknown phenotypes).
Procedure—Dogs were considered normal, equivocal, and affected for TVD on the basis of echocardiographic appearance of the tricuspid valves. Information on related dogs was collected for estimation of heritability of the 3 categories of phenotype, using a threshold model. Complex segregation analysis was performed to evaluate the possibility of the effect of a major locus on TVD.
Results—Heritability of TVD in this population of dogs was found to be 0.71, a value sufficiently large to suggest a segregating major locus. Subsequent complex segregation analysis did not provide sufficiently strong evidence to indicate influence of a major locus on the prevalence of TVD. However, complex segregation analysis for 2 categories of phenotype (eg, equivocal dogs were grouped with affected dogs) suggested that there was a single recessive allele with a substantial impact on the expression of TVD.
Conclusion and Clinical Relevance—In Labrador Retrievers, TVD is a heritable disorder. Affected dogs and dogs closely related to affected dogs should not be used for breeding. There was insufficient evidence to suggest the influence of a major locus on TVD, although this conclusion was affected by the classification of dogs for diagnosis of the condition. (Am J Vet Res 2002;63:816–820)
