Genetic welfare problems of companion animals

 

Osteochondrodysplasia

 

Breed: Scottish Folds

 

Condition:  Osteochondrodysplasia

Related terms:Scottish fold osteodystrophy

Outline: Osteochondrodysplasia is a developmental abnormality that affects cartilage throughout the body. It is this that causes the abnormal ear shape in Scottish fold cats. Its effects in other parts of the body, especially the limb bones, are much more serious, causing severe distortion of limb bone shapes and severe arthritis. The disease can be apparent in animals as young as 7 weeks and persists throughout life. It causes crippling, lameness and serious chronic pain. There is no cure. Cessation of breeding from any cats with folded ears would eliminate this condition very promptly.



 

Summary of Information

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1.           Brief description

The feature that defines the Scottish fold breed is the forward folding of the ears. This folding is due to osteochondrodysplasia, a developmental abnormality of the cartilage which would normally support the ear. Osteochondrodysplasia also has devastating effects on cartilage and bone development elsewhere in the body.

The Scottish fold breed originated in Scotland in the 1960s from matings of a cat with a naturally occurring mutation in which its ears folded forward, to local farm cats and British Shorthairs. The breed became recognised by the governing council of the Cat Fancy of Great Britain a few years later. However, by 1974 it had been excluded from their list of recognised breeds due to the crippling deformity of the limbs and tail that was evident in the breed. It is also banned by the Fédération Internationale Féline, an international cat fancy society. Breeders in the USA and elsewhere in the world have continued to perpetuate the breed (Malik et al 1999).


All cats with folded ears develop osteochondrodysplasia. In cats which are homozygous for the abnormal gene (ie having two copies of it), a progressive, crippling arthritis develops early in life whilst in those which are heterozygous (with only one mutant gene), the arthritis tends to progress more slowly (Malik 2001).


Affected cats may be grossly deformed, with short wide limbs and a short, inflexible tail. They show lameness, swollen wrist (carpal) and ankle (tarsal) joints, have an abnormal gait, and are reluctant to move and jump. Severely affected individuals become crippled and unable to walk.

 

2.           Intensity of welfare impact             


In all homozygous folded-eared cats this condition causes deformities and progressive joint disease leading to crippling disability associated with significant pain. Many affected cats are euthanased earlier in life due to the profound effects of this disease.

In some heterozygous individuals the condition may be very mild but in others there can be significant joint disease and deformity leading to pain and disability.

 

3.           Duration of welfare impact

 

In homozygous cats, lesions and bone abnormalities are evident on x-rays from 7 weeks of age (Jackson 1975). Significant disease has been shown to occur in some heterozygous individuals from as young as 6 months of age (Matthews et al 1995, Malik et al 1999).

 

4.           Number of animals affected

 

All homozygous cats are severely affected. All heterozygous individuals are affected but to varying degrees(Malik et al 1999, Chang et al 2007).

 

5.           Diagnosis

The diagnosis can be confirmed with radiographs (x-rays) or using CT (computer tomography) or MRI (magnetic resonance imaging) scans.

 

6.           Genetics

 

Osteochondrodysplasia in Scottish folds is an autosomal dominant condition which is now believed to have incomplete dominance (ie the possession of a dominant gene does not completely mask the effect of the other gene that has been inherited (Takanosu et al 2008)).

 

7.           How do you know if an animal is a carrier or likely to become affected?

There are no carriers of the gene which are not, themselves, affected: all folded-eared cats develop osteochondrodysplasia to some extent.

 

8.          Methods and prospects for elimination of the problem

 

Cessation of breeding from any cats with folded ears would eliminate this condition within a generation (Malik et al 1999).

 

 


 

For further details about this condition, please click on the following:

 

 

 

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1.           Clinical and pathological effects

The feature that defines the Scottish fold breed is their forward folded ears. This characteristic develops at 3-4 weeks of age (Malik et al 1999) and is due to a defect in the ear cartilage such that it is unable to support the weight of the ear, which then flops forward as a result.

Cartilage is an important structural tissue. In the adult it gives support and structure to parts of the body that lack bone, such as the external ears. It is also intimately associated with bones, forming the smooth surfaces of joints allowing easy, pain-free movement. In addition, cartilage plays a key role in bone growth and development in the young animals. The skeleton of foetuses is initially formed of cartilage that is gradually replaced by bone. Growth in the length of long bones is due to the proliferation and laying down of cartilage in special sections of the bone – the disc-shaped growth plates – near each end. As growth continues the cartilage produced is replaced by bone, in a process called endochondral ossification. Abnormalities in the development of cartilage can thus have far reaching effects on normal joint and bone formation as well as on the formation of body parts which depend upon the presence of cartilage in adulthood.


The osteochondrodysplasia seen in the Scottish fold breed is caused by an autosomal dominant gene (labelled Fd) (Jackson 1975, Malik et al 1999), which Takanosu et al (2008) suggest shows incomplete dominance (ie the possession of a dominant gene does not completely mask the effect of the other gene that has been inherited.)


Osteochondrodysplasia is seen in all Scottish fold cats which have a copy of the Fd gene, but  homogyzous (Fd/Fd) cats are more severely affected than those that are heterozygous (Fd/fd) (Malik 2001, Takanosu et al 2008).


Scottish Fold Osteochondrodysplasia (SFOCD) in homozygous Fd/Fd cats

The most consistent finding in homozygous Scottish fold cats is an abnormally thick tail which is inflexible at the base. This is due to the tail bones being abnormally short and wide and fused together. The limbs of homozygous individuals are also deformed, having short feet. The metatarsal and metacarpal bones (the bones that connect the toes to the wrist (carpus) and hock (ankle/tarsus), and also the toe bones to a lesser extent, are distorted and widened. With time, the joints of the lower parts of the limbs become diseased and inflamed (osteoarthritis) and excessive amounts of new bone (exostoses) is laid down around these joints, adding to the joint inflammation and ultimately leading to joint fusion.


From their studies, Malik et al (1999) concluded that the initial developmental abnormalities of the limb bones are probably due to defective endochondral ossification in these bones and that, thereafter, because of the abnormal mechanical forces that result from the limb deformities, secondary degenerative joint disease (osteoarthritis) occurs; with inflammation of the tissue lining the joint capsule (synovitis) and abnormal bone development around the joint. They also suggested that abnormal articular (joint) cartilage may play a role in the rapid development of arthritis (inflammation of the joints). The abnormal periarticular bone, that forms in the joint capsule and in tendon insertions around the joints, is so extensive in some cases, that it may come together and connect around the sides of the joint, resulting in it becoming fused (ankylosed).


These disease processes lead to limb deformity, reduced ability to bear weight, abnormal gait and lameness. These progress such that affected cats are unable to walk (Malik et al 1999).


Scottish Fold Osteochondrodysplasia (SFOCD) in heterozygous Fd/fd cats:

In heterozygous individuals the primary developmental deformities tend to be less severe. However, these animals invariably suffer from progressive arthritis in multiple limbs (Malik 2001). This usually develops later in life than that seen in homozygous individuals but its development is variable (Malik et al 1999, Chang et al 2007). Heterozygous individuals tend to show signs of disease once arthritis and the bony exostoses have started to develop (Malik et al 1999). Some show only mild disease, whilst others show such severe problems that the cat has to be euthanased for welfare reasons (Malik et al 1999).


There is no cure for this condition, although permanent medication with pain-relieving drugs and chondroprotective treatments may help alleviate the pain. Long-term use of pain killers can in itself produce undesirable side effects in cats. Mathews et al (1995) reported that surgery to fuse the affected joints and remove the bony exostoses was helpful in decreasing lameness (and presumably pain) and Hubler et al (2004) reported that radiation therapy appeared to relieve pain in one individual.

 

 

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2.               Intensity of welfare impact

In homozygous (Fd/Fd) cats the bone deformities result in an abnormal body shape and gait and rapidly progress to cause painful joint disease and severe disability, significantly affecting the cat’s quality of life from a young age.

The disease can range from mild to severe in heterozygous (Fd/fd) individuals. Affected individuals have cartilage which is unable to stand up to the agile and athletic life-style that is normal for cats (Malik 2001). Joint disease causes significant pain in some individuals with lameness and a reluctance to move or jump, leading to significant disability. Affected cats may be euthanased for welfare reasons.

 

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3.           Duration of welfare impact

 

In homozygous cats, bone abnormalities are evident on x-rays from 7 weeks of age (Jackson 1975). By 6 months of age gross bony growths, particularly around the hock and metatarsals can be felt and seen on x-rays (Malik et al 1999).

Significant disease has been shown to occur in some heterozygous individuals from as young as 6 months of age (Matthews et al 1995, Malik et al 1999).


The disease is progressive and incurable, and so affected cats they will suffer from the disease throughout their life.

 

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4.           Number of animals affected

 

It was shown in 1975 that all homozygous cats are severely affected. For some time it was thought that heterozygous individuals were not affected. However, this has now been shown not to be the case and it now appears that all heterozygous individuals are affected but to varying degrees (Malik et al 1999, Chang et al 2007).



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5.           Diagnosis

 

The disease can be confirmed with x-rays (radiographs) or using CT (computer tomography) or MRI (magnetic resonance imaging) scans.

 

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6.           Genetics

Osteochondrodysplasia in Scottish folds is an autosomal dominant condition, which is now believed to have incomplete dominance (Takanosu et al 2008). All homozygous Scottish fold cats have two mutant genes (Fd/Fd) and have severe disease. All heterozygous individuals (ie those with one mutant gene (Fd/fd) also develop the condition but it is often milder (Malik et al 1999, Chang et al 2007, Takanosu et al 2008).

 

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7.           How do you know if an animal is a carrier or likely to become affected?

There are no carriers of the gene which are not themselves unaffected: all folded-eared cats develop osteochondrodysplasia to some extent. Cats with normal ears produced from the mating of a folded-eared cat to a non-folded eared cat are genetically fd/fd and do not have the mutated gene or the condition. These cats are called Scottish shorthairs or Scottish fold variants and they do not have SFOCD.

Both Malik et al (1999) and Takanosu et al (2008) recommended that cats with folded ears should not be bred from, whether homozygous or heterozygous. Scottish fold owners have professed their desire to maintain this breed because of its temperament. Malik et al (1999) pointed out that if owners want a cat with a similarly sweet temperament they might wish to consider a Scottish shorthair which differs only in that it is free of the abnormal disease-causing gene.


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8.          Methods and prospects for elimination of the problem

Cessation of breeding from any cats with folded ears would eliminate this seriously crippling and painful condition within a generation (Malik et al 1999).

 
 

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9.          Acknowledgements

UFAW is grateful to Rosie Godfrey BVetMed MRCVS and David Godfrey BVetMed FRCVS for their work in compiling this section and to Emily Jewell for her contribution to it.

 

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10.          References

Chang J, Jung J, Oh S, Lee S, Kim G, Kim H, Kweon O, Yoon J and Choi M (2007) Osteochondrodysplasia in three Scottish fold cats. Journal of Veterinary Science 8: 307–309

 

Feline Advisory Bureau (FAB) (no date) Scottish fold: Inherited problems in cats. Available from http://www.fabcats.org/breeders/inherited_disorders/scottish_fold.php.  Accessed 2.2.11


Hubler M, Volkert M, Kaser-Hotz B and Arnold S (2004) Palliative irradiation of Scottish fold osteochondrodysplasia. Veterinary Radiology and Ultrasound 45: 582–585

 

Jackson OF (1975) Congenital bone lesions in cats with folded-ears. Bulletin of The Feline Advisory Bureau 14: 2–4

 

Malik R. (2001) Genetic diseases of cats. Proceedings of ESFM symposium at BSAVA congress 2001, Birmingham, UK

 

Malik R, Allan GS, Howlett CR, Thompson DE, James G, McWhirter C and Kendall K (1999) Osteochondrodysplasia in Scottish fold cats. Australian Veterinary Journal 77: 85–92

 

Mathews KG, Koblik PD, Knoeckel MJ, Pool RR and Fyfe JC (1995) Resolution of lameness associated with Scottish fold osteodystrophy following bilateral ostectomies and pantarsal arthrodeses: a case report. Journal of the American Animal Hospital Association 31: 280–288

 

Takanosu M, Takanosu T, Suzung H and Suzung K (2008) Incomplete dominant osteochondrodysplasia in heterozygous Scottish fold cats. Journal of Small Animal Practice 49: 197–199

 

 

© UFAW 2011

 

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