Program in Equine Medical Genetics (subcontract)

Miniature horses are the product of selection for small stature with good conformation. However, it appears that selection for small stature can inadvertently result in selection for genes causing dwarfism. However, dwarfism has been characterized in horses with reference to human dwarfism (Naviaux, 1999). Preliminary studies by John Eberth and Thomas Swerczek, co-PIs on the study, demonstrated that there are at least 4 types of dwarfism among miniature horses based on phenotypic appearance and clinical evaluation. The most common form of dwarfism among miniature horses (Type I) appears similar to acromesomelic dysplasia dwarfism in humans in both its clinical appearance as well as its recessive mode of inheritance. Radiographs and tissue samples are in hand for 20 horses with Type I (crania-facial malformation, shortened limbs), 4 from horses with type 2 (like Femoral Hypoplasia: body is same but legs are shortened), 3 ftom horses with type 3 (Kniest Syndrome disproportionate stature with short, barrel shaped chest. Crania-facial malformations with large head and retinal detachment and degeneration) and I with type 4 (like dwarfism in dexter cattle). Specific Aims: Compare SNP profiles between horses with Type I dwarfism to miniature horses with normal stature. Compare SNP profles between horses with Type II dwarfism to miniature horses with nomal stature.