Osteochondrodysplasia (Scottish Fold Disease)

The Scottish Fold's folded ear — the trait that makes the breed instantly recognisable and enormously popular on social media — is a cartilage defect. That is not an editorial framing; it is the biological mechanism. A dominant mutation in the TRPV4 gene weakens the cartilage of the ear so that it collapses forward. The difficulty is that the gene is not expressed only in the ear.

Cartilage forms the growth plates of every long bone and the smooth bearing surface of every joint. In a cat carrying the fold mutation, that cartilage develops abnormally throughout the skeleton, producing a condition called osteochondrodysplasia. Bone forms in irregular, lumpy deposits around the joints of the ankles, wrists and tail vertebrae; joint surfaces become uneven; and secondary arthritis follows. The tail is often the earliest giveaway — short, thick and unable to flex, so that running a hand down it feels like running a hand down a length of dowel rather than a chain of small mobile bones.

Severity depends on dosage. A kitten that inherits the mutation from both parents — the outcome of mating two folded cats — can be visibly crippled before it is six months old, with grossly swollen limbs and a gait so painful that euthanasia is sometimes the kindest option. Breeders responded to this decades ago by mating folds only to straight-eared cats, which avoids the catastrophic homozygous form. But research using radiographs, most notably work from Australia and later studies in Europe, has repeatedly found skeletal changes in heterozygous cats too. The consensus among veterinary radiologists is that there is no such thing as a Scottish Fold with entirely normal joints; there are only folds whose disease has not yet been looked for or has not yet become obvious.

For the owner of an affected cat, the practical task is recognising pain. Cats do not limp dramatically or cry; they simply stop doing things. They take the stairs instead of the leap, sleep on the floor instead of the windowsill, become less tolerant of being picked up, and are described as having "always been a quiet cat". Modern feline pain management is much better than it was — the anti-NGF monoclonal antibody injections in particular have transformed chronic joint pain treatment in cats — and many owners are astonished by how much personality returns once analgesia is optimised.

The wider question is one of breeding ethics rather than medicine, and the veterinary profession has been increasingly direct about it. A trait that is inseparable from a painful skeletal disease cannot be selected against while still selecting for the trait, because they are the same gene.