Appendix

Formerly known as IMM, Myosin-heavy chain myopathy (MYHM) is a muscle disease in Quarter Horses and related breeds that results in two distinct clinical disease presentations, immune-mediated myositis (IMM) and non-exertional rhabdomyolysis. Both presentations involve muscle loss or damage and are linked to the same genetic variant.

Hereditary equine regional dermal asthenia (HERDA) is an inherited skin condition primarily found in Quarter Horses that is characterized by hyperextensible skin, scarring, and severe lesions along the back of affected horses.

Tobiano is a white spotting pattern characterized by white on the body that crosses the topline.

Classic Roan is a white patterning coat color trait characterized by intermixed white and pigmented hairs in the body while the head, lower legs, mane, and tail remain colored.

The extension gene, or red factor, determines whether a horse will have a chestnut base coat color or a black or bay base coat color.

Dominant white is a variable white spotting pattern caused by many different mutations in the KIT gene. The VGL tests for the five most common mutations known as W5, W10, W13, W20, and W22. Homozygosity for W5, W10, W13 or W22 is thought to be non-viable.

Cream is a dilution that causes the palomino, buckskin, smoky black, cremello, perlino, and smoky cream coat colors.

Appaloosa Pattern-1 is a modifier of the leopard complex spotting (LP) and controls the amount of white in the coat pattern.

The agouti gene controls the distribution of black pigment, and determines whether a horse will have a bay or black base coat color.