New variants in ACE gene region in 10 Cavalier King Charles Spaniel dogs with mild and severe myxomatous mitral valve disease - preliminary study.

Myxomatous mitral valve disease is the most common acquired cardiac disorder in dogs, with particularly high prevalence and early onset in Cavalier King Charles Spaniels. Activation of the renin-angiotensin-aldosterone system plays a key role in disease progression, and genetic variation in the angiotensin-converting enzyme gene may influence disease severity and therapeutic response. The aim of this study was to characterize angiotensin-converting enzyme gene variation in a Polish Cavalier King Charles Spaniel population with mild and severe myxomatous mitral valve disease using targeted next-generation sequencing, with emphasis on the rs850683722 polymorphism. Ten client-owned dogs diagnosed with myxomatous mitral valve disease were prospectively enrolled and classified according to American College of Veterinary Internal Medicine guidelines into mild (stage B1) and severe (stage C/D) groups. Dogs with comorbidities or receiving medications affecting the renin-angiotensin-aldosterone system were excluded. Genomic DNA isolated from peripheral blood underwent next-generation sequencing to cover coding exons and adjacent intronic regions of the angiotensin-converting enzyme gene. Variant detection and annotation were performed using standard bioinformatic methods. A total of 188 variants were identified, of which 95,2 % were intronic. Coding variants were rare and included one missense substitution, one in-frame insertion, and three synonymous changes. Fourteen variants were novel. The rs850683722 polymorphism was present in both groups without clear association with disease stage. No variant showed a strong relationship with disease severity. Overall, angiotensin-converting enzyme gene variation was dominated by non-coding polymorphisms with potential regulatory effects, suggesting a modifying rather than causative role in disease progression.