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
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)