Gene mutation linked to wasting disorder in Quarter horses

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"A" shows a normal muscle mass in an MYH1 E321G homozygote horse prior to developing IMM. B shows the same horse four months after an episode of IMM. The spine is prominent due to loss of epaxial muscles (arrow). C shows wasting of the middle and superficial gluteal muscles (arrow) is present. Photos: Finno et al. https://doi.org/10.1186/s13395-018-0155-0
“A” shows a normal muscle mass in an MYH1 E321G homozygote horse prior to developing IMM. B shows the same horse four months after an episode of IMM. The spine is prominent due to loss of epaxial muscles (arrow). C shows wasting of the middle and superficial gluteal muscles (arrow) is present. Photos: Finno et al. https://doi.org/10.1186/s13395-018-0155-0

Researchers have linked a mutation in the MYH1 gene to a muscle-wasting condition most commonly seen in Quarter horses.

Carrie Finno and her colleagues linked the missense mutation in the gene to immune mediated myositis (IMM), in which the immune system of horses attacks the skeletal muscles, causing rapid wasting of the muscles along the topline.

The condition is rare in horses, but is the most common cause of rapid wasting of the topline in Paint  and Quarter Horses.

The study team, writing in the journal Skeletal Muscle, said causes of autoimmune diseases such as IMM are not well understood, but environmental stimuli, combined with a genetic predilection, appear to be important factors.

It is more likely to affect horses aged under 8, or older horses aged over 17, research has shown.

Because most horses affected by IMM are of Quarter Horse-related breeds, and since certain stallions appear to be overrepresented in the genetic lineage of QHs with the disorder, the researchers hypothesized that there was an underlying genetic variant that causes susceptibility to the condition.

The study team described their genetic analysis of 36 Quarter horses with IMM and 54 breed-matched unaffected horses from the same environment.

The E321G mutation in the MYH1 gene which they identified was found to be highly associated with susceptibility to the condition.

The MYH1 gene encodes for myosin, a motor protein.

“This is the first report of a mutation in MYH1 and the first link between a skeletal muscle myosin mutation and autoimmune disease,” they reported.

Further, they said it was the first report of a mutation in the MYH1 gene associated with susceptibility to a specific myopathy.

IMM is normally treated with corticosteroids.

The study team comprised Carrie Finno, Giuliana Gianino, Sudeep Perumbakkam, Zoë Williams, Matthew Bordbari, Keri Gardner, Erin Burns, Sichong Peng, Sian Durward-Akhurst and Stephanie Valberg. They are variously affiliated with the University of California, Davis; Michigan State University; and the University of Minnesota

A missense mutation in MYH1 is associated with susceptibility to immune-mediated myositis in Quarter Horses
Carrie J. Finno, Giuliana Gianino, Sudeep Perumbakkam, Zoë J. Williams, Matthew H. Bordbari, Keri L. Gardner, Erin Burns, Sichong Peng, Sian A. Durward-Akhurst and Stephanie J. Valberg
Skeletal Muscle 2018 8:7 https://doi.org/10.1186/s13395-018-0155-0

The study, published under a Creative Commons License, can be read here

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