Earfold and Osteochondrodysplasia (Discovered in the Scottish Fold)

Scottish Fold cats are bred for their uniquely folded ears, a feature which starts to occur in kittens around four weeks of age. Unfortunately, the same variant that causes this ear phenotype also causes a skeletal condition called osteochondrodysplasia. Osteochondrodysplasia is a condition that causes abnormal development of joints and cartilage and results in skeletal malformations. Previously, the inheritance pattern was thought to be recessive but today it is known to be codominant. Cats with two copies of the genetic mutation (homozygotes) develop severe, progressive osteoarthritis early in life with radiographic evidence of lesions present as early as seven weeks of age. Cats with one copy of the mutation (heterozygotes) develop more variable signs of the disease, ranging from mild osteoarthritis to a more moderate to severe form. The mild form of the disease usually develops in late middle age or the geriatric years while the moderate to severe form of the disease develops in early adulthood with radiographic evidence of lesions present as early as six months of age. Typical findings include shortened and malformed metatarsal and metacarpal bones, narrowed joint spacing in the distal limbs, and secondary development of degenerative joint disease. The tail is also often shortened and inflexible. These changes can cause short, misshapen limbs, abnormal posture and gait, lameness, and pain. The disease is progressive and incurable and many severely affected cats are euthanized early in life due to welfare concerns.

Severity of the disorder, which is progressive and incurable, can be confirmed with radiographs, CT, or MRI. Osteoarthritis can be treated in the same way as other forms of degenerative joint disease including environmental modification, nutraceuticals, GABA analogues, and nonsteroidal anti-inflammatory drugs when appropriate. The disease can be palliated with an acceptable quality of life in most mild to moderately affected individuals. However, many severely affected cats are often elected to be euthanized due to welfare concerns.

There are many responsibilities to consider when breeding cats. Regardless of test results it is important that your cat is in good general health and that you are in a position to care for the kittens if new responsible owners are not found. For first time or novice breeders, advice can be found at most cat registry websites.

This condition is autosomal dominant meaning that one copy of the mutation is needed for signs to occur. If the desire is to produce cats with the breed defining trait of folded ears, it is advised to only breed carrier cats with one copy of the Earfold mutation to clear cats with no copies of the Earfold mutation. This will decrease the likelihood of kittens in the litter developing the severe form of the disease. About half of the kittens will have one copy of the Earfold mutation and half will have no copies of the Earfold mutation. Carrier to carrier matings are not advised as the resulting litter will likely contain kittens with two copies of the Earfold mutation and these kittens are more likely to develop the severe form of the disease. Suspected carriers should be tested prior to breeding. Please note: It is possible that disease signs similar to the ones caused by the Earfold mutation could develop due to a different genetic or clinical cause.