Genetic basis of Dilated Cardiomyopathy in Manchester Terriers and English Toy Terriers - is caused by a missense mutation in the ABCC9 gene. The specific mutation is c.3557G>A, resulting in an amino acid change p.(R1186Q). The ABCC9 gene encodes a regulatory subunit of ATP-sensitive potassium channels in heart muscle cells, crucial for cardiac cell function and electrical stability. The disease is inherited in an autosomal recessive pattern—dogs must have two copies of the mutation (homozygous) to be at risk of developing the condition and experiencing sudden cardiac death or DCM. Carrier dogs (with one copy) do not develop disease but can pass the mutation to offspring.
Pathophysiology - causes progressive weakening and enlargement of the heart chambers, impairing heart function. The ABCC9 mutation disrupts potassium channel function, leading to myocardial degeneration and arrhythmias, which can result in sudden death in young dogs before the heart enlarges visibly. Histological findings include myocardial degeneration, fibrosis, inflammation, and sometimes mineralization.
Clinical Presentation and Age of Onset - Two clinical forms: Acute form: sudden death of apparently healthy puppies, usually between 2 months and 2 years of age (most by 6 months). Chronic form: detectable DCM with typical heart failure signs; may be associated with cryptorchidism (undescended testicles) in males.
Why This Matters to Breeders and Vets - Genetic testing enables breeders to identify carriers and avoid breeding two carriers, thereby reducing affected puppies and eliminating the mutation from the breed population. Veterinarians can target preventive care and monitoring for at-risk dogs identified by genetic testing to mitigate sudden death risk. The mutation has a carrier frequency of about 8-9% in these breeds, making screening important for sustainable breeding