Genetic Diseases

Decided to make this post because this is a topic of intense frustration for me. There are multiple issues with this topic, the primary one being lack of knowledge and negligence. If you’re going to be breeding animals for anything other than personal consumption, including selling them to others, you NEED to be aware of potential genetic diseases and their effects on the animals.

Some species of animals have such a vast and healthy gene pool that genetic diseases do not exist, however animals who are commonly bred as pets or performance animals generally have at least one, if not multiple, potential genetic diseases that they can be affected by.

So, what are genetic diseases?
Simply put, genetic diseases are any disease that is hereditary and can be passed from parent to offspring through genes. Additionally, the ONLY way for a genetic disease to be passed from one animal to another is through breeding and genes. For instance, a common cold, is NOT a genetic disease. Syphilis is also NOT a genetic disease – though it can be passed from parents through offspring (via the act of giving birth), it is not passed on genetically. Equine Hyperkalemic Periodic Paralysis Disease (HYPP) IS a genetic disease, affecting horses. It is ONLY passed on from parents to offspring through genes.

Where did genetic diseases come from?
Genetic diseases can often occur when breeding animals of unknown quality or genetics. An unknown or questionable gene pool can introduce genetic diseases into otherwise very healthy animals. Genetic diseases likely came about many years ago due to breeding a close-knit gene pool in an effort to achieve specific traits (such as specific colors, heavy muscling, or other varying “desirable” factors). Breeding animals within one specific gene pool can display desirable traits, but it will also amplify negative traits as well, including genetic diseases. Genetic diseases can also be caused by gene mutations, and additionally, when breeding in a small gene pool, the likelihood that these mutations will be passed on and couple up with other mutated genes is far more likely than when breeding vastly unrelated stock.

How are diseases displayed and carried?
Many genetic diseases in animals are displayed in 3 forms (we will use the letters D/N to display the theoretical diseases we are talking about):
– NN: homozygous recessive or an animal that is NOT affected
– D/N: heterozygous carrier or an animal that is not affected but carries one copy of the gene that can cause the disease
– DD: homozygous dominant or an animal that IS affected by the disease
For example, in dogs, Centronuclear Myopathy (CNM) would be displayed as NN for a dog that does not carry the disease, D/N for a dog carrying one copy of the gene, and DD for a dog carrying two copies which is affected by the disease.
Some genetic diseases, however, are homozygous OR heterozygous affected diseases (dominant disorders), HYPP in equines is one example. These diseases are as seen below:
– NN: animal is not affected nor a carrier
– D/N: animal is a carrier of one copy of the gene, and IS affected by the disease
– DD: animal is a carrier of both copies of the gene and is also affected by the disease
In this case, in order to have a disease-free animal with ZERO chance of passing the disease to its offspring, only NN animals should be bred.

What animals are affected by genetic diseases?
Generally, pretty much ALL animals can be affected by genetic diseases. Cats, dogs, and horses are among the most commonly diseased animals as they are typically bred and interbred extensively in order to obtain valuable traits. Any animals bred for conformation or showing can be affected by genetic diseases if they are too closely bred for too long.

How do I know if my animal has a genetic disease?
Almost EVERY breed or species registration database offers genetic testing to include the primary genetic diseases for that specific species or breed. For example, the website PawPrintGenetics offers testing for nearly every breed of dog. Most large animal veterinarians will pull 3 or 5 panel disease tests for horses depending on risk factors and breeding. For production animals, genetic diseases can be expelled by culling those animals who display traits for a disease, no testing needed.

Why are genetic diseases bad?
The effects of the diseases varies by disease and species. Some diseases can cause symptoms such as tremors or seizures, blindness, collapse, and death. HYPP in horses causes muscle tremors and twitching of varying degrees, EIC (exercise induced collapse) does exactly that in canines, and lethal white (breeding two overo horses to one another) causes death of the resulting foal.

What can we do about genetic diseases?
Responsible breeding is the MOST important factor affecting the spread of genetic diseases. If you have an animal (dog/horse, etc.) that you’re planning on breeding, do your homework. Determine what genetic diseases could possibly affect your animal, determine if either of the animal’s parents were carriers or affected by any genetic diseases, and have your animal tested for any potential diseases. Do NOT breed your animal if they are affected by any genetic diseases.
Most people don’t think about the fact that making the responsible decision NOT to breed even carrier animals (who are not affected, but carry the gene) can complete eradicate genetic diseases in a single generation. This is the reason that genetic testing is SO important! Knowing the outcome of a breeding and genes of animal even before breeding is vital to knowing whether or not to spend money on offspring that may carry a disease. Do your research, and only buy animals from responsible and reputable breeders. Not only will a responsible breeder offer genetic test results, but will also have animals that are fully inoculated and health tested, to ensure a high quality of offspring.

End points? Be responsible in your breeding. Don’t breed animals who carry or are affected by genetic diseases. Do your research and learn about the animals you’re trying to breed. If you’re not willing to take the time and spend the money on proper testing, don’t breed! There’s enough junk in the world that we don’t need any more junk added to it.

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