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Dermatomyositis

Dermatomyositis (DMS) is an immune-mediated inflammatory disease affecting Collie, Old-Time Scotch Collie, Rough Collie, Scottish Collie, Shetland Sheepdog, Smooth Collie, characterized by early-onset skin lesions and potential muscle inflammation, leading to muscle atrophy, difficulty eating, and a stiff-legged gait, with symptoms typically peaking around one year of age.

Affected Genes: DRB1, MAP3K7CL, PAN2

Inheritance: Complex Inheritance

Variant(canFam6):
MAP3K7CL chr31:24124800: ACTCCACAAA>GACT; PAN2 chr10:691178 G>A, DRB1 DRB1*002:01 (not avaiable yet

Breed: Collie
Old-Time Scotch Collie
Rough Collie
Scottish Collie
Shetland Sheepdog
Smooth Collie

General Information: Dermatomyositis (DMS) is an immune-mediated inflammatory disease affecting the skin and muscles, often seen in dogs before six months of age. Skin lesions typically precede muscle lesions, starting as small swellings that become pustules, ulcers, and crusty hairless regions, affecting areas like the muzzle, foot pads, around the eyes and lips, ears, and bony prominence. The disease usually peaks around one year of age, with some dogs showing improvement over time. In severe cases, muscle inflammation can lead to atrophy, difficulty eating, and a stiff-legged gait, with potential complications such as stunted growth and aspiration pneumonia. Treatment focuses on managing skin lesions and regulating the immune system, though relapses are common and severe lesions may result in scarring.

Genetics for dermatomyotis is complex. Research into the genetic cause of DMS has identified variations in three genome regions: PAN2 (Locus A), MAP3K7CL (Locus B), and DLA-DRB1 (Locus C), associated with increased risk. The normal alleles for Loci A and B are represented by “a” and “b,” while the risk alleles are “A” and “B”; for Locus C, the risk allele is “C” and others are “c.” Reliable genetic testing is crucial for responsible breeding practices, and it is recommended to avoid breeding dogs that will produce high-risk genotypes. For example, breeding an “aa” genotype dog with a “bb” genotype dog will not produce moderate or high-risk puppies. Other causes of DMS may exist, so a normal genetic test result does not exclude the possibility of similar genetic diseases.

References:
Berger D: Canine Dermatomyositis. Clinician's Brief 2016 14(11) pp. 50-52.

Evans JM, Noorai RE, Tsai KL, Starr-Moss AN, Hill CM, Anderson KJ, Famula TR, Clark LA. Beyond the MHC: A canine model of dermatomyositis shows a complex pattern of genetic risk involving novel loci. PLOS Genetics 2017 12(2)

Miller WH, Griffin CE, Campbell KL: Familial canine dermatomyositis. Muller and Kirk’s Small Animal Dermatology Saunders Elsevier 2013 pp. 585-587.