Dermatomyositis (DMS)

Dermatomysitis (DMS) is an autoimmune disease with a genetic background and additional environmental triggers. The disease is characterized by lesions of the skin on body-parts with minimal muscle overlay in affected Collies and Shetland Sheepdogs. While the onset of the disease is very variable, first symptoms might occur at about 12 weeks of age. Typical symptoms include hair loss and crusts in areas of legs and feet, the face and ears and the tail. In some cases, those symptoms weaken or disappear, sometimes even reappear during the life of a dog. In contrast to Shetland Sheepdogs, Collies often exhibit muscular dysfunctions like a high stepping gait, difficulties to swallow, drink and eat or muscle atrophy of the head and neck. The gold standard for the direct diagnosis of DMS is a skin biopsy. The genetic test analyses three variants that determine the risk for DMS. The complex multifactorial genetic trait needs an additional external trigger like vaccination or viral infection to cause symptoms of the disease. Stress-related factors are described to worsen the course of DMS. The likelihood of an individual dog developing DMS can be classified as low (0%-5%), moderate (33%-50%), or high (90%-100%) based on the genotype combination of locus A (PAN2), locus B (MAP3K7CL), and locus C (DLA-DRB1). Wild type alleles of loci A and B are represented by lower case letters, a and b, while the risk alleles are represented by upper case letters A and B. The risk allele at DLA complex (DLA-DRB1*002:01) is referred to as C, and the lower case letter c represents any alternate allele for DLA-DRB1. Low-risk genotypes: aabbCC, aabbCc, AabbCC, AabbCc, aaBbCC, aaBbCc, AaBbCC, AaBbCc, aaBBCc Moderate-risk genotypes: AAbbCC, AAbbCc, aaBBCC, AaBBCc, AABbCc High-risk genotypes: AABbCC, AaBBCC, AABBCC, AABBCc Breeding recommendation: High-risk genotypes (especially: AABB, AaBB, AABb) should be avoided in offspring. Matings should be chosen accordingly.