Prevalence of rs850683722 Variant and Its Influence on the Course of Myxomatous Mitral Valve Disease in 105 Cavalier King Charles Spaniel Dogs in the Polish Population.

Myxomatous mitral valve disease (MMVD) is the most common acquired cardiac disease in small-breed dogs and shows particularly high prevalence and early onset in Cavalier King Charles Spaniels (CKCS). Although MMVD is considered a complex, polygenic disease, the clinical relevance of individual genetic variants remains incompletely understood. The angiotensin-converting enzyme (ACE) gene variant rs850683722 has previously been associated with altered ACE activity and differences in renin-angiotensin-aldosterone system-related responses in dogs with MMVD. The aim of this study was to determine the prevalence of rs850683722 in a Polish population of CKCS dogs and to assess whether this variant is associated with the clinical course of MMVD. A total of 105 CKCS dogs were included in the study. All dogs underwent standardized cardiovascular evaluation, including echocardiography, electrocardiography, and systolic blood pressure measurement. MMVD diagnosis and staging were performed according to current ACVIM consensus criteria. Genotyping of the rs850683722 variant was performed using Sanger sequencing for 95 dogs, while next-generation sequencing data was obtained for 10 dogs. Genotype distribution, allele frequencies, conformity with the Hardy-Weinberg equilibrium (HWE), sex-related differences, and associations between genotype and age at progression to selected MMVD stages or the primary clinical endpoint were assessed statistically. The most frequent genotype was AA, detected in fifty-nine dogs, followed by GG in thirty-seven dogs and AG in nine dogs. When dogs carrying at least one A allele were considered variant-positive, the overall prevalence of the variant-positive genotype was 64.8%. The calculated allele frequencies were 0.605 for the A allele and 0.395 for the G allele. The observed genotype distribution deviated markedly from the Hardy-Weinberg equilibrium, mainly because of a pronounced deficit of heterozygous dogs. No significant association was detected between genotype and sex. Genotype was also not significantly associated with age at progression to stage B2 or stage C. A statistically significant difference in age of death was demonstrated by genotype, but this difference was not reflected in the survival analysis. The rs850683722 variant was highly prevalent in the studied Polish CKCS population, with a frequency comparable to previously reported data for this breed. Despite its documented biological association with ACE activity and RAAS-related responses, the variant was not significantly associated with the clinical progression of MMVD in this cohort. These findings suggest that rs850683722 alone seems unlikely to be a reliable marker for predicting the severity or rate of MMVD progression in Polish CKCS dogs. Further studies including larger cohorts, longer follow-up, pedigree information, and the direct assessment of RAAS activity may help clarify whether this variant has stage-dependent or treatment-related clinical relevance.