Novel Cardiac Troponin-I Missense Variant (c.593C>T) Is Associated With Familial Hypertrophic Cardiomyopathy in Golden Retrievers.

Abstract

Background: Hypertrophic cardiomyopathy (HCM) is a naturally occurring cardiac disorder afflicting humans, cats, rhesus macaques, pigs, and rarely dogs. The disease is characterized by maladaptive left ventricular wall thickening. Over 1500 sarcomere-coding mutations explain HCM in humans, whereas only 3 have been reported in cat breeds. To date, no mutations have been described in dogs. HCM in a nuclear family of Golden Retrievers was identified following the sudden cardiac death of 3 related puppies <2 years of age from 2 dam-offspring repeat matings.

Methods: Whole-genome sequencing on the 3 affected puppies, along with nuclear family members (ie, sire, dam, 4 unaffected littermates, 4 unaffected half-siblings), and 1 distantly related, geriatric, cardiovascularly normal Golden Retriever was performed (n=14). Candidate variant genotyping was performed in an unphenotyped cohort of dogs (n=2771) and an expanded population of phenotyped, unrelated Golden Retrievers (n=45). Left ventricular tissue immunofluorescence staining was subsequently performed to investigate incorporation and expression of mutant protein within the cardiac sarcomere of HCM-affected cases.

Results: Gross and histopathologic evaluations of the HCM-affected puppies revealed hallmark features of the disease, including cardiomyocyte hypertrophy, interstitial fibrosis, and left-sided congestive heart failure. Segregation analysis of called variants, performed under assumptions of an autosomal-recessive mode of inheritance, identified a single segregating c.593C>T missense variant in TNNI3 (Cardiac Troponin-I). This variant was not observed in the unphenotyped (n=2771) nor in the phenotyped, unrelated cohort of dogs (n=45). Immunofluorescence staining of left ventricular tissues did not reveal obvious aberrant protein localization and expression at the sarcomeric level, suggesting the molecular pathogenesis of the TNNI3 variant is not related to abnormal protein incorporation within the sarcomere.

Conclusions: This variant represents the first-ever reported HCM-associated variant in any canine species, and its identification holds promise for establishing translational models, genetic screening, and early disease prevention within the breed.