Common Feline Inherited Diseases
Diseases that are genetically determined are referred to as genetic diseases or hereditary diseases. It is often cited that there are about 250 hereditary diseases identified among cats so far. But how often do they occur?
Most domestic felines are random-bred. This causes for random frequencies of liability genes and random development of clinical genetic diseases among them. However, pedigreed breeds may have higher or lower incidences of certain genetic conditions depending on the frequencies of liability genes showing up in their generally much smaller gene pools. Therefore, purebred cats are more often than not at a higher risk from certain hereditary diseases than mixed breeds. This is why many people today want to know the breed composition of their felines in order to get a glimpse of what their pets may be at high risks from. Today, we will take a moment to briefly address some of these genetic conditions identified in cats and discuss which breeds are noted to be at the highest risks from them.
"DNA is the fundamental molecule the carries genetic instructions that help build the living world. Humans have DNA. Pigs have DNA. Even bacteria and some viruses have DNA too. The genetic instructions encoded in DNA inform how our bodies develop, grow, function. And in many cases, that same information can trigger disease." - biotech entrepreneur Sebastian Kraves.
Polycystic Kidney Disease
Polycystic kidney disease (PKD) is an inherited disorder that can lead to feline kidney failure. In this disease, small fluid-filled cysts are formed in the feline kidneys. PKD is the most common single-gene feline disorder identified so far. Affecting 6% of cats worldwide, this condition is present in 38% of Persian cats. It is also very frequent among Persian-derived breeds such as Himalayans. Affected cats are always heterozygous for the gene causing for PKD, as the gene in homozygous form is lethal (Eaton KA et al, 1997).
Hypertrophic cardiomyopathy (HCM) is the most common feline heart disease. HCM causes the left ventricle of a cat’s heart to thicken, which decreases the space available for blood to flow. This means that a smaller amount of blood is pumped through the cat’s body with each heartbeat compared to a healthy cat. In order to compensate, HCM cats have an increased heart rate (tachycardia). Tachycardia and heart rhythm abnormalities can be a clue that your veterinarian should test your cat for HCM.
HCM can be caused by several genetic mutations. In Maine coon cats a mutation in the myosin-binding protein C gene has been identified and it occurs in 33% of cats of this breed. This mutation is autosomal dominant. In 20% of Ragdolls different mutations have been identified to cause the condition. A genetic test is available for breed-specific mutations for HCM in both of these breeds (Longer M et al, 2013)(Borgeat K et al, 2014).
Diabetes mellitus (DM) is a metabolic disorder in which blood sugar levels remain high for long periods of time. This occurs when there isn’t enough insulin being produced in the body or the body isn’t responding to it. Without insulin sugar from the blood can’t be transmitted to the target cells and tissues. As a consequence, despite high blood sugar levels, the body cells and tissues are starving. Luckily, diabetes can be successfully treated. This condition is commonly diagnosed among felines, interestingly, primarily random-bred cats. However, according to some studies, some breeds such Burmese, Siamese, Norwegian forest, Russian blue and Abyssinian seem to be at a higher risk from diabetes (O’Leary CA et al, 2013)(Cooper RL et al, 1997-2007)(Ohlund M et al, 2015).
Feline Lower Urinary Tract Disease (FLUTD)
Feline lower urinary tract disease or FLUTD is a term used to address multiple conditions associated with the lower urinary tracts in cats. It includes bladder inflammation (cystitis), urethra inflammation, a formation of urinary stones in the bladder (urolithiasis) and urethral obstructions. Feline idiopathic cystitis and >feline urologic syndrome have been observed as the most common feline hereditary predisposition in practice. According to studies (Dorsch R et al, 2014), (Defauw PA et al, 2011) and (Stella J et al, 2013), FLUTD affects about 1-2% of domestic cats. Persians seem to be at a higher and Siamese at a lower risk from FLUTD (Buffington CA et al, 2006).
"Most practitioners recognize that once diagnosed and controlled, signs associated with FLUTD can recur if owners are not diligent about controlling predisposing factors. Such measures can include minimizing environmental stress, maintaining anti-inflammatory or behavior-modifying drugs that decrease the likelihood for bladder inflammation, and maintaining dietary control for cats predisposed to crystalluria." - recommends Jerold S. Bell, DVM, Cummings School of Veterinary Medicine at Tufts University.
Progressive Retinal Atrophy
Progressive retinal atrophy (PRA) is a genetically determined condition that causes blindness in mid to late life in cats. Two genes have been identified to be associated with the condition. The identified genes are associated with Abyssinian, Somali and Ocicat breeds. The genes are recessive, which means only homozygous carriers are affected. Unfortunately, the condition isn’t treatable, but there are many ways in which we can help blind cats have a happy and satisfying life.
Deafness is a relatively common condition among white cats, specifically white cats with one or both eyes blue in color. The dominant allele W of the white masking gene causes disrupted replication and migration of melanocytes into the skin. All the cats carrying this allele (W/W and W/w) will appear white, even if they carry other color genes. Only recessive homozygotes (w/w) will express the normal pigmentation. Carriers of this W allele are at a much higher risk from deafness in comparison to non-carriers. This is because this gene doesn’t only interfere with the coat (and eye) color but also with the development of structures within the ears and can occasionally cause the degradation of the cochlea (a part of the inner ear involved in hearing).
To learn more about feline eyes and relatedness of odd and blue eyes and deafness please read about heterochromia. For more information about the relatedness of white coat and deafness please read about cat coat genetics.
Generally speaking, inherited diseases are much less common among cats than dogs. This is because cats are often less target-bred and random breeding ensures a larger and richer gene pool. This increases the number of gene variants and decreases the frequency of defective genes causing for certain diseases. However, some genetic diseases are still very frequent regardless of this. Conditions addressed above seem to be the ones with the highest incidences among our favorite pets. "Other common feline diseases with hereditary components include lymphocytic inflammatory disease, calcium oxalate bladder stones, allergic skin disease with or without eosinophilic granuloma complex, mammary tumors, and lymphoma." - Jerold S. Bell, DVM, Cummings School of Veterinary Medicine at Tufts University. Recognizing common diseases and patients at highest risks can help improve their diagnosis, prognosis and treatment.
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