The Scottish Fold breed of cat has a genetic mutation that affects the development of cartilage. The most obvious outward manifestation of this is making the ear cartilage fold so the ears bend forward, giving the cat its characteristic appearance.
Unfortunately, the genetic defect that causes abnormality of the ear cartilage also causes severe abnormalities of the cartilage of bones – there will be defective bone development and severe bone and cartilage abnormalities in all cats with folded ears. These bone abnormalities lead to severe and painful arthritis.
The genetics of osteochondrodysplasia
The mutation causing osteochondrodysplasia results from a single autosomal dominant gene, although the gene may have incomplete penetrance, and thus the abnormalities may vary in severity between one cat and another.
All Scottish Fold cats suffer from variable degrees of painful degenerative joint disease, which can result in fusing of the tail, tarsi (ankles) and stifles (knees). This is apparent clinically as a reluctance to move, and abnormal posture and gait, lameness and short misshapen limbs.
International Cat Care believe that it is simply unethical to continue to breed cats with a genetic mutation that is known to cause significant painful disease – the rationale for breeding these cats was purely human pleasure, as some people believe the folded ears look appealing. This is an unnatural appearance for a cat though, and the underlying genetic defect has far reaching and severe consequences for the health of the cat.
More information is needed about other breeds of cats with folded or curly ears before we can be certain that they too do not have defects that may cause other problems.