Testing of dogs: ARVC
Arrhythmogenic right ventricular cardiomyopathy (ARVC) in Boxers
ARVC is a degenerative heart disease characterized by atrophy of heart muscle cells and fat deposition in heart cells. It affects predominantly the right ventricle. It is a life-threatening disease and may lead a sudden death.
The first clinical signs occur in adult dogs, mostly at the age of six years. The signs have different form. One apparent form of the disease is characterized by sudden short episodes of collapsing (syncope), seizures and inability to exercise normally and irregular heartbeats (arrhythmias). Other forms of this disease are associated with general signs of congestive heart failure such as breathlessness, coughing, lethargy, weakness, fatigue, palpitation or fluid build-up in abdomen. In case of hidden forms, no clinical signs are observed and typical arrhythmias can be detected only by thorough heart examination. Dogs with no clinical signs present a great hazard to healthy breeding of boxers. It often happens that the affected dogs do not show any signs for a long time and the only expression of the disease is the sudden death due to arrhythmia.
For a long time, it has been considered that the disease is caused by the causal mutation in STRN-gene for striatin. Striatin is a protein that contributes to normal cardiomyocyte cell-to-cell adhesion and mechanical stability of the heart muscle cells. The mutation in this gene (striatin) leads to loss of normal cellular linking and development of arrhythmias. The mutation has autosomal dominant pattern of inheritance with incomplete penetration. It means that the disease may or may not develop in heterozygous dogs that inherited the mutant allele from one of its parents. The disease will generally develop in homozygous individuals that inherited the mutant allele from both parents.
The recent studies have proven that this mutation is not directly responsible for ARVC, however, is closely associated with the development of ARVC. Namely, there is a clear linkage between the STRN-gene mutation and the ARVC-phenotype. The gene responsible for this disease is located near striatin on the same chromosome (CFA17) and the mentioned association is a result of meiotic recombination. The striatin mutation increases the severity of the clinical symptoms. With almost 100% probability, dogs homozygous for striatin mutation will be ARVC-affected and the clinical signs will occur at earlier age than in heterozygous dogs. Moreover, the STRN-mutation can increase the severity of the disease or symptoms of other heart diseases.
Whereas the STRN-mutation is clearly associated with ARVC in boxers, the studies have shown that also other unknown mutations play their role in this disease.
However, the STRN is still a very important marker of a not yet identified gene locus located on the same chromosome that is directly responsible for development of ARVC in boxers. The testing for STRN-mutation is used to identify dogs with causal mutation for ARVC.
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Reference:
B. M. Cattanach, J. Dukes-McEwan, P. R. Wotton, H. M. Stephenson, R. M. Hamilton: A pedigree-based genetic appraisal of Boxer ARVC and the role of the Striatin mutation; Vet Rec. 2015 May 9;176(19):492. doi: 10.1136/vr.102821. Epub 2015 Feb 6.