Dilated cardiomyopathy (DCM) in Schnauzer

Dilated cardiomyopathy (DCM) is a severe heart disorder, typically affecting large dog breeds. In most breeds, the disease is unknown, so-called idiopathic; in some breeds inclusive Schnauzer the disease is caused by a genetic disorder.

The DCM is a condition in which the heart´s ventricular walls are stretched and the walls become thinner.  Thinning of the walls causes enlargement of the ventricles and in most cases the left heart ventricle is affected first. These changes result in worsened function of the heart, the heart´s ability to contract and to pump the required amount of blood. The perfusion of the bodily organs is poor; systemic oedemas and pulmonary oedema occur resulting in dyspnoea and coughing. The symptoms of the disease also include ventricular arrhythmia and myocardial scarring.

The first clinical signs occur between the first and the third year of age.  At the early stage of DCM, the affected dogs show reduced tolerance to physical stress and overall weakness, fainting and collapse. The prognosis is not good and DCM is the most common cause of invalidity and untimely death of dogs.

The DCM in Schnauzer is caused by a mutation in RBM20-gene, specifically by 22-bp deletion shifting the reading frame during the synthesis of RBM20.  A premature stop codon is introduced leading to the changes in properties and function of the resulting protein. The RBM20 binds RNA and acts as a regulator of mRNA splicing in a group of genes involved in heart development. Non-functional RBM20 produces aberrant isoforms of TTN, a gene encoding the largest known protein titin, expressed in skeletal and heart muscles, where it is responsible for sarcomeres flexibility.

The mutation shows autosomal recessive mode of inheritance. It means that the mutation will be expressed only in individuals that inherit the mutant allele from each parent (recessive homozygote). A heterozygote is an individual that inherited the mutant allele from one parent and shows no symptoms and is clinically healthy but can pass the mutant allele to its offspring.

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Reference:

Molecular genetic studies of canine inherited diseases including SAMS, neuronal ceroid lipofuscinosis and dilated cardiomyopathy: Gilliam, Douglas H., Jr., Johnson, Gary S., University of Missouri 2016