Evidence of genetic contribution to patellar luxation in Toy Poodle puppies

Patellar luxation (PL) is one of the most common orthopedic disorders in dogs and a genetic factor is considered to play an important role in the development of PL. Genomic analysis has attempted to identify the genetic markers associated with the development of PL but only suggestive markers have been identified. Carefully selecting breeds with higher incidence rates of congenital PL as well as affected dogs with more severe symptoms are required, but such information remains limited to date. This study aimed to assess the genetic contribution to the development of PL in puppies. Using data on PL from 2,048 puppies of the nine common breeds in Japan, the association of PL grades between the limbs, breed, and sex as well as the concordance of PL between littermates were examined. A significant correlation was found between right and left limbs in PL grades in all the puppies (Spearman rank correlation coefficient (rs)=0.91, P < 0.001) and for each breed (rs=0.81-0.93, P < 0.001). In total, 20.3% of the puppies were affected. The inter-breed difference in PL prevalence was 2.1-38.1%, and Toy Poodles showed the highest prevalence rates. Littermates of the affected puppies with PL grade >= 2 had a 16.2-fold higher risk (P < 0.001). Thus, these results suggest that PL in puppies is primarily influenced by genetics, especially in Toy Poodles. These data highlight the necessity of using a breeding scheme to decrease the prevalence of PL.