Amyloidosis is a diverse group of diseases that can be seen in many different animals.
Amyloid is a type of inert protein, and amyloidosis describes the disease that occurs when this protein is deposited within body organs where it may disrupt normal function.
Although there are various recognised causes of amyloidosis, familial systemic amyloidosis is well recognised in cats (although uncommon) and can have an inherited basis.
Systemic amyloidosis in Abyssinian cats
Familial systemic amyloidosis was recognised in Abyssinian cats in the USA and characterised in the 1980s. Affected cats developed amyloid deposits primarily in their kidneys resulting in chronic kidney disease typically before they were 6 years of age. The amyloid was derived from ‘serum amyloid A’ – an acute phase (inflammatory) protein. The genetics of this condition were not fully determined, but with selective breeding it has become much less prevalent.
Systemic amyloidosis in Siamese and other cats
Systemic amyloidosis has also been described in domestic shorthair cats, Siamese cats, and other breeds. In these cats, amyloid accumulation can occur in various organs including the intestines, liver, and kidneys. Kidney accumulation can lead to chronic kidney disease, whereas accumulation in the liver often causes hepatomegaly and a very fragile liver. Spontaneous rupture of the liver, with often fatal bleeding into the abdomen, is not uncommon.
An inherited predisposition has been identified in Siamese cats, and in affected cats it has been demonstrated that there is a gene mutation that results in the formation of an amyloidogenic form of serum amyloid A (SAA) protein (in normal cats this protein does not result in amyloid deposition).
It is thought that disease results from the combination of an abnormal gene (causing an abnormal structure of the SAA protein), and also infectious or environmental factors that cause systemic inflammation and so increase the production of this protein in affected cats.
The genetic basis and mode of inheritance of these disorders are not yet clear.