Scottish Fold Osteochondrodysplasia
Scottish Fold osteochondrodysplasia is an inherited bone and cartilage disorder specific for this cat breed. It belongs in a wider group of disorders, generally known as osteochondrodysplasia, but the form occurring in the Scottish Fold breed is specific by its causative mutation. Osteochondrodysplasia is a disorder (”dysplasia”) of bones (”osteo”) and cartilage (”chondro”). It can be characterized into group of musculoskeletal disorders, a broad category of diseases that affects the muscles or bones.
The Scottish Fold is a breed of domestic cat, specific by its ”folded” ears, which are bending forward and down towards the front of their head. This phenotype is caused by a dominant gene mutation which affects the cartilage throughout the body. Although it causes appealing look of the cat because of its folded ears, it also causes severe cartilage abnormalities which lead to severe and painful arthritis. The evident deformities caused this breed to be excluded the list of recognized breeds in 1974, also by the Fédération Internationale Féline, an international cat fancy society. However, breed is still being maintained by breeders in the USA and elsewhere in the world.
Affected cats show painful bone deformity, appearing as short wide limbs and a short, inflexible tail. They exhibit lameness, swollen wrist and ankle joints, abnormal gait, and are reluctant to move and jump. In more severe cases, cat is completely unable to walk.
The disorder can be diagnosed based on history and examination. Examination includes imaging of limbs, by usage of radiology, bone scan, MRI and spiral CT. As the Scottish Fold osteochondrodysplasia is caused by a dominant gene, homozygous cats appear to be more severely affected than the heterozygous. In homozygous cats can be identified on x-ray already from 7 weeks of age, while in heterozygous cats it can be evident from 6 months of age.
Currently there is no treatment for Scottish Fold osteochondrodysplasia.
Scottish Fold osteochondrodysplasia is caused by a substitution mutation in TRPV4 gene (transient receptor potential cation channel, subfamily V, member 4). This gene is encoding a calcium permeable ion channel and is expressed in various tissues, including chondrocytes, osteoblasts and osteoclasts. TRPV4 gene correct activity is important for cell differentiation and tissue homeostasis. Various mutation within this gene have been associated with different human skeletal dysplasias.
Scottish Fold osteochondrodysplasia is inherited in an autosomal dominant pattern and both homozygous and heterozygous for the mutation cats will develop symptoms. Homozygous cats appear to develop symptoms earlier than the heterozygous cats and their symptoms appear to be more severe.
Gandolfi, B. Et al. (2016): A dominant TRPV4 variant underlies osteochondrodysplasia in Scottish fold cats. Osteoarthritis Cartilage. 2016 Aug;24(8):1441-50. doi: 10.1016/j.joca.2016.03.019. Epub 2016 Apr 6.