The most common cardiovascular disease in domestic dogs is myxomatous mitral valve disease (MMVD), accounting for 75% of all cardiac disease. An increase in age is generally associated with increased incidence of the disease, but Cavalier King Charles Spaniels (CKCS) exhibit an unusually high prevalence of early-onset MMVD, and thus, potentially greater cardiac morbidity and mortality compared to other breeds. Previous research has suggested that selected candidate risk alleles for MMVD are fixed in CKCSs, including six locations within the Nebulette (NEBL) gene on CFA2. The current study analysed genotypes of 180 Australian CKCSs at the identified risk loci. Of these, 178 were phenotyped for severity of disease by echocardiographic measurements of left atrium to aortic root ratio (LA:Ao) and weight normalised left ventricular end diastolic diameter (LVIDdN). Genotyping array markers correctly predicted the genotype at the risk-variant loci in the CKCS population, and the NEBL1, NEBL2 and NEBL3 variants were observed to be in perfect linkage disequilibrium in this cohort. The CKCS cohort included 6/178 dogs being heterozygous for the protective/wild-type alleles at the NEBL locus. The mean LA:Ao and LVIDdN scores of these dogs heterozygous at NEBL1-3 variants were significantly smaller, and with significantly lower variance compared to age-matched CKCSs that were homozygous for risk alleles. The lower cardiac measurements in the heterozygous dogs indicate a significantly reduced risk of severe MMVD disease. Our analysis suggests that despite relative fixation of the NEBL risk alleles, healthy reference alleles at NEBL1-3 exist in low frequency in the CKCS breed and can be used to reduce MMVD severity and mortality.

Primary ciliary dyskinesia (PCD) is a clinical syndrome that in dogs primarily manifests as chronic respiratory disease associated with cilial malfunction. The current study employs whole‐genome sequencing and a candidate gene approach to uncover the genetic basis of PCD in three Cocker Spaniel siblings following diagnosis of their respiratory cilia by scanning electron microscopy and high‐speed video microscopy. Absence of the disorder in the parents suggested autosomal recessive inheritance. A 29 bp frameshift insertion in the eleventh exon of the candidate gene sperm‐associated antigen 1 ( SPAG1 ) [NC_049234.1:g.2213788_2213789insGGCGGCGGCAAGCGGCCGGAGAGGGGCGC] was identified as likely causative for PCD in this family. The 29 bp frameshift variant was unobserved in a public variant call file including 1987 dogs from the Dog10K resource however an in‐frame insertion was sometimes observed at the same locus. A Cocker Spaniel with similar symptoms from a different family tested negative for the identified variant suggesting that there are multiple causes for the condition in Cocker Spaniels.