Scottish Fold Osteochondrodysplasia
The Scottish Fold is a purebred domestic cat, characterized by autosomal-dominant gene mutation causing the ears to fold forward and downward.
Although this trait contributes to the breed's unique appearance, this genetic anomaly affects cartilage through the body and can causes severe health problems, such as the Scottish Fold Osteochondrodysplasia (SFOCD).
Scottish Fold osteochondrodysplasia (SFOCD) is an inheritable disorder characterized by generalized disturbance of endochondral ossification, resulting in skeletal deformation particularly in the distal limbs, ears and tail.
Scottish Fold kittens that do not develop folded ears are known as Scottish Straights.
Clinical signs:
Clinical signs are typically lameness, stiff stilted gait, reluctance to run and jump, short deformed distal limbs, swelling of plantar tarsometatarsal & palmar carpometacarpal regions and short thick inflexible tails.
These ambulatory difficulties are secondary to progressive skeletal disease and osteoarthritis caused by defective maturation and dysfunction of cartilage. The severity of clinical signs, rate of progression and extent of radiographic abnormalities, vary from case to case.
Diagnosis
SFOCD can be diagnosed early through screening radiographs, since lesions are radiographically evident by 7 weeks of age.
Radiographic features of SFOCD include irregularity in the size and shape of tarsal, carpal, metatarsal and metacarpal bones, phalanges, and caudal vertebrae, narrow joint spaces, and progressive new bone formation around joints of distal limbs with diffuse osteopenia of adjacent bone. A plantar exostosis caudal to the calcaneus is present in advanced cases. Subsequently, these skeletal alteration may progressively evolve into ankylosing polyarthropathy of the distal limb joints.
Etiology:
According to a recent study, the gene mutation responsible for SFOCD has been identified and it has been shown that c.1024G>T in the transient receptor potential vanilloid 4 (TRPV4) gene lead to abnormal osteochondrogenesis. This mutation is unique to Scottish Fold cats since it has not been identified in other breeds.
One study suggested that the fold trait is inherited as an autosomal dominant trait, while a later study suggested an incomplete dominance. A cat with folded ears may have either one (heterozygous) or two copies (homozygous) of the dominant fold gene (Fd). Both phenotypes (folded ear pinna and osteochondrodysplasia) are linked and inherited in an autosomal dominant manner. Therefore, mating cats that have folded ear pinna is contraindicated. SFOCD cannot be predicted only by the presence of the ear pinna phenotype, especially in cases of heterozygosity c.1024G>T in TRPV4.
Symptoms in heterozygous cats are considered less severe than homozygous cats, results in mild lesions of the extremities and seem to impair the cat’s quality of life in a less significant manner.
Therefore, if no exostoses are palpable, it is strongly advised to proceed with radiographic examination and/or genotyping of TRPV4 for identification of the presence of the Scottish Fold cat strain among cross breed cats.
Treatment:
There is no specific treatment or cure for this disease. Treatment options are noncurative, but palliative.
Most commonly used are nonsteroidal anti-inflammatory drugs (NSAIDs), joint supplements or a combination of the two.
It has been shown that some patients may respond to pentosan polysulfate injections subcutaneously, and others may benefit from an oral glycosaminoglycan preparation with amelioration of clinical signs. Chondroprotective agents such as glucosamine and chondroitin sulfate, may minimize cartilage damage, increase joint lubrication and enhance new cartilage production.
In severe cases refractory to medical management, surgical approaches such as ostectomy, and pantarsal/pancaspal arthrodesis, or palliative irradiation is optional. Radiation therapy may be useful to relieve pain but is not curative for severe exostosis.
It is recommended to take regular serial radiography of affected cats to identify progression of degenerative joint lesions over time.
Prognosis and further suggestions:
It is suggested that all Scottish Fold cats suffer from Osteochondrodysplasia of some degree, and that the severity and duration of symptoms and radiographic lesions depend on genetic types (homozygous vs heterozygote).
Cats homozygous for the gene (Fold-to-Fold matings) developed progressive skeletal changes, including epiphyseal and metaphyseal deformities, secondary osteoarthritis and exuberant exostosis around the distal extremities early in their lives, compared to heterozygote with much milder joint disorders later in their life.
Therefore, the proposed solution is to avoid breeding cats with folded ears and instead use cats with a normal ear conformation such as Scottish shorthair
Sources:
Takanosu M, Hattori Y. Osteochondrodysplasia in Scottish Fold cross-breed cats. J Vet Med Sci. 2020 Dec 26;82(12):1769-1772.
Takanosu, M.; Takanosu, T.; Suzuki, H.; Suzuki, K. (April 2008). "Incomplete dominant osteochondrodysplasia in heterozygous Scottish Fold cats". The Journal of Small Animal Practice. 49 (4): 197–9.
Malik R, Allan GS, Howlett CR, Thompson DE, James G, McWhirter C, Kendall K. Osteochondrodysplasia in Scottish Fold cats. Aust Vet J. 1999 Feb;77(2):85-92.
Chang J, Jung J, Oh S, Lee S, Kim G, Kim H, Kweon O, Yoon J, Choi M. Osteochondrodysplasia in three Scottish Fold cats. J Vet Sci. 2007 Sep;8(3):307-9.
Gandolfi B., Alamri S., Darby W. G., Adhikari B., Lattimer J. C., Malik R., Wade C. M., Lyons L. A., Cheng J., Bateman J. F., McIntyre P., Lamandé S. R., Haase B.2016. A dominant TRPV4 variant underlies osteochondrodysplasia in Scottish fold cats. Osteoarthritis Cartilage 24: 1441–1450.
Hubler M, Volkert M, Kaser-Hotz B, Arnold S. Palliative irradiation of Scottish Fold osteochondrodysplasia. Vet Radiol Ultrasound. 2004 Nov-Dec;45(6):582-5.
