Scottish fold osteochondrodysplasia

What it is

Scottish fold osteochondrodysplasia is a developmental disorder of cartilage and bone. It is caused by a dominant variant of the TRPV4 gene, which encodes an ion channel in chondrocytes. The same variant makes the ear cartilage weak so that it folds forward, the trait that defines the breed: this is why the folded ear and the disease are inseparable. Articular and growth cartilage develop abnormally, and over time bony deformities, exostoses (bony proliferations) around the distal joints and progressive osteoarthritis appear.

Inheritance is incompletely dominant: homozygous cats, born from mating two fold-eared cats, have severe, early lesions; heterozygous cats, born from mating a Scottish fold with a straight-eared cat, also develop lesions, usually milder and later. There is no fold-eared Scottish fold free of the disease. On welfare grounds, some cat registries do not recognise the breed and breeding fold-eared cats is restricted in some countries.

Who it affects

Fold-eared Scottish fold cats and crosses carrying the variant, such as some cats of related breeds. Homozygous cats show signs from the first months of life; heterozygous cats often in adulthood or with age. Most straight-eared cats of the breed do not carry the variant, but some heterozygous kittens are born with folded ears that straighten as they grow, so only the genetic test rules it out.

Anatomy involved

• Distal pelvic limbs: the tarsus, metatarsus and phalanges are most severely affected; the bones are short and misshapen and large plantar exostoses form around the tarsus that can eventually fuse the joints.
• Distal thoracic limbs: similar lesions in the carpus, metacarpus and digits, usually less marked.
• Tail: short, wide, irregularly shaped caudal vertebrae; the tail is thick, short and stiff, and the cat cannot flex it normally.
• Ears: folded auricular cartilage.

Clinical signs

Lameness, a stiff or stilted gait, reluctance to jump and move, abnormal postures (such as sitting with the pelvic limbs stretched out) and a stiff tail that is painful when handled. In advanced cases hard bony masses can be felt around the tarsi and carpi, and the feet are short and wide. Chronic pain may show only as reduced activity, lack of grooming or changes in temperament.

Diagnosis

• Breed and folded ears with compatible signs.
• Examination: tail stiffness (assessed by flexing it gently, without forcing) and pain and thickening of the distal joints.
• Radiographs of the feet, tarsi, carpi and tail: short, misshapen bones, narrowed joint spaces, periarticular exostoses, especially plantar to the tarsus, and ankylosis in advanced cases.
• Genetic test for the TRPV4 variant.

Treatment

There is no cure; treatment is palliative and aims to control chronic pain: non-steroidal anti-inflammatories (such as meloxicam) with monitoring of kidney function, anti-nerve growth factor monoclonal antibodies licensed for feline osteoarthritis in some countries, gabapentin, chondroprotective supplements and weight control. In selected cases palliative radiotherapy of the exostoses, resection of the exostoses and tarsal arthrodesis have been used. The environment is adapted with ramps, low-sided litter boxes and accessible beds. The most important measure is prevention: not breeding fold-eared cats.

Key studies

• Gandolfi et al. (2016), a genome-wide association study of 44 Scottish folds and 54 controls. It identified the TRPV4 p.V342F (c.1024G>T) variant, associated with both the folded ear and the osteochondrodysplasia; it was absent from 648 unaffected cats. In cells, the mutant channel showed altered activity.
• Rorden et al. (2021), a radiographic survey of 22 genotyped Scottish folds, assessed by four reviewers blinded to ear shape. All 10 fold-eared cats were heterozygous and none of the 12 straight-eared cats carried the variant. Fold-eared cats scored worse on average, but their changes were much milder than in earlier reports. The sample is small.
• Velie et al. (2023), VetCompass records of 1131 Scottish Fold and 117 Scottish Shorthair cats in Australia (1992–2018). Only 12 Scottish folds had a clinical diagnosis of osteochondrodysplasia and another 69 cats were suspected cases; diagnosed cats were usually under 30 months old. It measures diagnoses recorded in first-opinion practice, not radiographic lesions.
• Matsumoto et al. (2026), 114 cats genotyped and photographed as they grew. Seven heterozygous cats had folded ears as kittens that straightened as they matured (12.7% of heterozygotes); their pinnae were smaller than those of straight-eared cats without the variant. Ear shape alone is not enough to identify carriers. The authors work for a genetic testing company.
• Ukawa et al. (2026), genotyping of 8610 cats of 14 breeds in Japan. As genetic testing was adopted, homozygous Scottish folds fell from 14.2% in 2017 to 1.9% in 2024, while the proportion of heterozygotes held steady. The variant was also found in the American Curl, Norwegian Forest Cat, Munchkin and Minuet. Same conflict of interest as the previous study.