PKD:

What is PKD?

Polycystic kidney disease (PKD) is an inherited condition that causes multiple cysts (pockets of fluid) to form in the kidneys. These cysts are present from birth. They start out very small but they grow larger with time and may eventually severely disrupt the kidney; when that happens the kidney can no longer work and kidney failure develops. The cysts usually grow quite slowly, so most affected cats will not show any signs of kidney disease until relatively late in life, typically at around seven or eight years old. However, in some cats kidney failure will occur at a much younger age and at the moment there is no way of predicting how rapidly the disease will progress in any particular cat.

How common is PKD in cats?

Unfortunately PKD has now become very common in some cat breeds. Persians and Exotic Shorthairs have the highest incidence of problems and studies around the world have shown that around one in three cats from these breeds are now affected by the disease. Other cat breeds that have been developed using Persian bloodlines, and breeds that have allowed outcrossing to Persian cats (eg British Shorthairs) may also have a proportion of affected cats, but in other unrelated breeds it is an extremely rare condition.

How is PKD inherited?

PKD is the result of a single, autosomal, dominant gene abnormality. This means that:-
- Every cat with the abnormal gene will have PKD; there are no unaffected carriers of the gene.
- Every cat with PKD will have the abnormal gene, even if that cat only has a few small cysts in its kidneys.
- A cat only needs one of its parents to be affected with PKD in order to inherit the abnormal gene.
- Every breeding cat with PKD will pass the disease on to a proportion of its kittens, even if it is mated with an unaffected cat.
- It appears that inheriting two copies of the abnormal gene, ie, one from each parent, causes such severe disease that the affected kitten dies before birth. All affected cats are therefore considered to be heterozygous (ie they carry one PKD gene and one normal gene).

Why has PKD become so common?

PKD doesn't usually cause kidney failure until quite late in life, so an affected cat may have been used to produce a large number of litters of kittens before it becomes ill itself.

Can PKD be cured?

Unfortunately there is no available treatment that will prevent the development of kidney failure in a cat that is affected by PKD. The cysts are present from birth and cannot be removed, nor can they be prevented from growing.

Once kidney failure has actually developed, treatment can be used to try to reduce the amount of work that the kidneys have to do, and to try to reverse the secondary effects of renal failure. Such treatment will improve the cat's quality of life, but will not alter the underlying disease or stop the cysts from growing larger.

Do all cats with PKD die of renal failure?

The number of cysts present in each kidney, and the rate at which the cysts grow, varies considerably from cat to cat. Severely affected cats or cats with rapidly growing cysts will develop renal failure at an early age, and will die from PKD. Most affected cats wil appear to be quite healthy until later in life. but will eventually succumb to renal failure and die from PKD. Some cats with few cysts or slowly growing cysts may remain healthy into old age, and may die from other conditions before renal failure develops.

Unfortunately there is currently no way to predict how quickly the condition will progress in an individual cat, and at what age renal failure will occur.

What can be done about PKD?

All cats that carry the abnormal gene are affected with PKD, and affected cats can be identified before they reach breeding age. This makes it relatively easy to eliminate the disease from a breeding group; if all cats in the high-risk breeds were to have their kidneys scanned before they were used for breeding, and if affected cats were not then used for breeding, then PKD could be eradicated from those breeds in a single generation.

Thanks to the Feline Advisory Bureau for the above information.
For further details on PKD visit http://fabcats.org/