Over 800 hereditary diseases have been described for dogs and new ones are discovered every year.
There are diseases that can be directly attributed to a specific defect in the genome (total of all genes); many diseases also involve multiple defects at the same time. For other diseases there is a so-called genetic disposition. Such a combination of certain genes alone does not cause a disease. However, if it encounters other favorable factors such as poor nutrition, animals with this genetic constellation will develop an illness more quickly than those without.
Chromosomes are the units in which a large part of the DNA is present as the carrier of the genetic material in the cells. Hereditary diseases can be distinguished according to the chromosome on which they are passed on: Inheritance via “normal” chromosomes is referred to as “autosomal” hereditary diseases; there are two of these chromosomes in every healthy organism. However, if one of the sex chromosomes is responsible for a disease, it is inherited as an X or Y chromosome (females have two X chromosomes, males have one X and one Y chromosome). In addition, hereditary diseases can be inherited in a dominant or recessive manner. Since there are duplicates of every chromosome in the body except for the sex chromosomes, both genes must be defective for a recessive disease to manifest itself. If the disease is inherited dominantly, on the other hand, one diseased gene is enough for it to break out. There are also diseases in which several genes are defective at the same time (polygenic inheritance). A certain number of damaged genes have to come together here for the disease to break out.
Autosomal recessive hereditary defects account for the largest proportion of hereditary diseases in dogs. Although it is known or strongly suspected that many diseases are hereditary, the associated inheritance is still unclear. For still other diseases there are already genetic tests to detect them.
By the way: Defects in the DNA and subsequent diseases can also be caused by environmental influences (e.g. medicines) or spontaneous mutations during pregnancy, so they are not always inherited!
Diagnosis of hereditary diseases in dogs
Pedigrees, in which the occurrence of the disease is noted for each animal in a family, are particularly helpful for detecting and understanding a hereditary disease in dogs. Due to increasing inbreeding
In the field of pedigree dogs, hereditary diseases have increased significantly. Attempts are already being made to counter this with breeding tests and the exclusion of diseased animals from breeding. However, some hereditary diseases only appear in combination with environmental factors. This sometimes only happens after the animal has already been used for breeding.
Puppies affected by hereditary diseases often show delayed growth and lower weight gains than their littermates. They often point
neurological disorders, i.e. disorders of the nervous system,
chronic gastrointestinal problems and
on. Depending on the disease, they gradually become weaker and die at a young age.
Some hereditary diseases in dogs are briefly outlined below.
Type of hereditary diseases
Syringomyelia: Various dog breeds, but especially Cavalier King Charles Spaniels, have a skull deformity. The cerebrospinal fluid (liquor) can then not circulate freely, which means that the pressure conditions change. Consequences are severe pain and itching in the head and neck area.
Elbow joint dysplasia (ED): ED is made up of several clinical pictures which, if left untreated, result in damage to the articular cartilage (osteoarthritis) of the elbow. Genetic factors and improper diet seem to play the main role in its development. For Labradors and Golden Retrievers, testing for ED is part of the breeding testing.
Hip dysplasia (HD): Disease particularly common in German Shepherds. Initially there is only a certain instability of the hip joint, later the HD leads to severe pain and arthrosis.
Dermoid sinus: This condition is particularly common in Rhodesian Ridgebacks. There is a connection between the surface of the skin and the deeper layers of tissue, sometimes as far as the spinal cord, and vertebral deformations. Infections up to meningitis are the result.
Brachycephalic airway syndrome: This disease occurs in brachycephalic, i.e. short-headed breeds such as boxers, pugs, bulldogs and Pekingese. The extremely short and round skull leads to several changes in the respiratory organs: The nasal conchae have too little space, which impairs the air flow and thermoregulation (temperature regulation). The soft palate is too long, the larynx cannot function normally, and the trachea is too small in diameter. This results in snoring breathing noises, shortness of breath and low resilience. The animals suffer particularly at high temperatures, some sleep sitting up and/or with their mouths open due to lack of air.
Portosystemic shunt: The portosystemic shunt is an inherited blood vessel malformation in the liver. There is a connection between the supplying blood vessel, which transports metabolic products from the intestine to the liver and the “normal” bloodstream. This partially or completely bypasses the detoxification function of the liver, which can lead to very different symptoms. Anything is possible, from mild illnesses that are only discovered by chance to very clear signs of illness. Many different dog breeds are affected.
Cancer diseases (neoplasia)
Many types of cancer have a genetic component, as is also known, for example, for human breast cancer. Since the origin of cancer is still not fully understood, other factors will certainly become known in the future.
Examples can be mentioned
hemangiosarcoma (malignant tumor of the blood vessel wall, often in the spleen, heart or liver) in Labrador Retrievers, German Shepherds and Boxers
skin melanoma (skin cancer) in Airdale Terriers, Scottish Terriers, Spaniels and Schnauzers and
the mammary carcinoma (mammary groin tumor) in the beagle.
Many defects in enzymes, e.g. for digestion or at other points in the metabolism, are inherited in an autosomal recessive manner. If the animals have a healthy gene, the defect usually goes unnoticed because small amounts of the enzyme continue to be produced. Only animals in which both genes are not working properly have serious metabolic problems.
The inheritance of diabetes mellitus (diabetes) in Wolfspitz and Samoyed dogs and ivermectin hypersensitivity in Australian Shepherds, Collies and Shelties are well known. Ivermectin is a common ingredient in dewormers, so care should be taken in herding dogs to avoid this substance or to check intolerance beforehand.
Many autoimmune diseases are also genetic or are promoted by genetic components. These include e.g. atopic dermatitis (severely itchy skin inflammation), pemphigus foliacaeus (also a skin disease with pustules and crusting) and lupus erythematosus (an autoimmune disease that attacks many different body cells and accordingly provokes different symptoms) in different breeds. For example, poodles, German shepherds, collies, beagles, Irish setters and Afghan hounds are more frequently affected by lupus erythematosus.
Inguinal hernia and umbilical hernia: In the case of a hernia, organ parts pass through a normally non-existent portal into other parts of the body. In the case of an umbilical hernia, for example, intestinal loops can suddenly be felt under the skin on the abdomen, in the case of an inguinal hernia, intestinal loops in the groin area come to the surface. Depending on the severity, this can be unproblematic, but if the blood vessels are pinched off, the intestine can be seriously damaged, which is why a veterinarian should always take a look at it. The inheritance of this is still unknown, the disease affects many dog breeds.
Dilated cardiomyopathy: Many breeds are affected by this degenerative heart disease, with different inheritances coexisting. However, it is often young dogs of large breeds such as St. Bernards, Great Danes or Dobermanns.
Torsion of the stomach: Large dog breeds in particular suffer from a torsion of the stomach. The gassed, overfilled and then twisted stomach must be treated by the veterinarian as quickly as possible to prevent circulatory failure.
Cauda equina syndrome: This back disease mainly affects larger dogs, but can occur in all breeds and is inherited as polygenic. The spinal cord is compressed by the intervertebral discs, which causes pain and later also paralysis.
Idiopathic epilepsy: Idiopathic always means that the exact cause is (still) unknown. Epilepsy is basically an excessive activity of brain cells (neurons), leading to seizures.
Narcolepsy: This falling asleep in fits and starts, in which the animals can be woken up, particularly affects Doberman Pinschers, Dachshunds and Labrador Retrievers and is inherited in an autosomal recessive manner.
Susceptibility to or resistance to infectious diseases can also be hereditary.