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Schnauzer Dilated Cardiomyopathy (DCM)
| Acronym: | DCM |
| Gene: | RBM20 |
| Mutation: | 22bp deletion |
| Inheritance: | Autosomal recessive |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
Schnauzer dilated cardiomyopathy (DCM) is a heart disorder that causes heart enlargement, resulting in inefficient blood pumping. Decreased function of the heart can have a negative impact on the lungs, liver, and other body systems. Generally, dilated cardiomyopathy is known to affect several dog breeds, such as Doberman Pinscher, Great Dane, Boxer, Cocker Spaniel, and Schnauzers. Although among these breeds affected dogs share the same symptoms, the causative mutation of the disorder differs. In schnauzers, the DCM causative mutation has been identified in Standard and Giant Schnauzers. Dilated cardiomyopathy is a part of a wider group of disorders, known as cardiomyopathies, which affect primarily the heart muscle. It is the most common heart disorder among dogs and human patients.
The left ventricle in the heart is one of four chambers. It is responsible for pumping oxygenated blood to tissues all over the body, while the right ventricle pumps blood only to the lungs. Dilated cardiomyopathy 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 whole heart. This dilatation causes the inability of the ventricles to pump the required amount of blood. DCM can also have an impact on the valves that separate the ventricles from the atrium, causing a backup of the blood in the circulatory system, entering fluids in the lung tissue, and lowering the oxygen that is available to the body’s tissues.
Schnauzer dilated cardiomyopathy (DCM) can be diagnosed by electrocardiography (ECG) and echocardiography (ultrasound), due to changes in the heart’s structure. Expansion of the walls of the left atrium and ventricle will be evident, as well as the heart’s reduced ability to contract. These changes happen in the so-called occult phase, and during this phase, the dog will show no evident symptoms. In the second phase of dilated cardiomyopathy in Schnauzers (DCM), the overt phase, the dog will show loss of appetite, increased heart rate, pale gums, exercise intolerance, difficulty breathing, and fainting. These symptoms may be evident, but not necessarily. At times, DCM’s only manifestation may be a dog’s sudden death. DCM seems to affect more commonly the giant dog breeds and is less common in smaller breeds. Also, male dogs seem to be more commonly affected than female dogs. Except for genetic causes, dilated cardiomyopathy in dogs can be caused by nutritional deficiencies, caused by a lack of Taurine amino acid. Also, several DCM cases in dogs were caused by a certain infection, such as by Trypanosoma and canine parvovirus.
Schnauzer dilated cardiomyopathy (DCM) is caused by a 22-bp deletion and frameshift in RBM20, the canine equivalent of a gene previously associated with DCM in humans. The disorder is inherited in an autosomal recessive pattern. Healthy parents of an affected puppy are obligate heterozygotes and therefore carry one mutant allele. Heterozygotes have no symptoms. Dogs homozygous for the mutation will display the symptoms of the DCM. When mating two asymptomatic carriers, at conception, each cub has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
CARRIER |
Tested mutation was detected in animal with „carrier“ result. Animal tested as carrier has one wild-type and one mutation allele, it is in heterozygous state. It will not develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
** Potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Gilliam, H. Douglas Jr. (2016): Molecular Genetic Studies of Canine Inherited Diseases Including Sams, Neuronal Ceroid Lipofuscinosis and Dilated Cardiomyopathy. A Dissertation presented to the Faculty of the Graduate School University of Missouri.