Evaluation of the Prevalence of Genetic Variants at the Nebulette Locus in Cavalier King Charles Spaniels

The Cavalier King Charles Spaniel (CKCS) exhibits an unusually high prevalence of myxomatous mitral valve disease (MMVD). A potential link to MMVD for allele risk variants near the heart specific nebulette (NEBL) gene has been identified. Although these allele risk variants seemed fixed in the CKCS, wild-type (healthy) allele variants at NEBL1-3 have likewise been found in a larger cohort, in which it was associated with less severe heart enlargement. The frequency of the healthy wild-type allele var-iants in the asymptomatic breeding population is unknown. Therefore, the aim of this study was to investigate the wild-type allele frequency through prospective genetic testing in a large sample of CKCS that were intended for breeding in both the Nether-lands and Australia. Blood samples of 371 CKCS with an unknown genetic status were collected, of which 175 from the Netherlands, and 196 from Australia. Deoxyribonu-cleic acid (DNA) was extracted for genotyping of NEBL allele variants. No dog was homozygous for the wild-type allele variants. Only 1 dog from the Netherlands was heterozygous, while 9 dogs from Australia were heterozygous for the wild-type allele variants. The prevalence of heterozygous dogs in the Australian breeding population was low (4.6%), but significantly higher compared to the prevalence in the Dutch breeding population (0.57%). In conclusion, selective breeding for the wild-type NEBL allele in the CKCS is nearly impossible, as it will result in the formation of a severe genetic bottleneck. Selection of breeding CKCS on wildtype NEBL variants should not be used on its own due to the low prevalence in this breed and due to the polygenic character of the disease.