American Paint Horse - Genetic Problems

Genetic Problems

One medical issue associated with the breed is the genetic disease lethal white syndrome (LWS). Also called Overo Lethal White Syndrome (OLWS) or, less often, White Foal Syndrome (WFS), it is linked to a recessive gene associated with the frame overo pattern. Horses that are heterozygous carriers of the gene do not develop the condition and are physically healthy. However, when a foal is born that is homozygous for the LWS gene, it should be humanely euthanized shortly after birth, or else will die within a few days from complications involving an underdeveloped intestinal tract. A DNA test is available for LWS so that horses who are carriers of this gene are not bred to one another. Horses can carry the LWS gene and not visibly exhibit overo coloring; cases have appeared in the offspring of both tobiano and solid-colored parents, though all cases to date are horses that had overo ancestors. LWS is also not unique to Paint Horses; it can occur in any equine breed where the frame overo coat pattern is found.

Due to the heavy influx of American Quarter Horse breeding, some Paints may also carry genetic disorders such as Hyperkalemic Periodic Paralysis (HYPP), Hereditary Equine Regional Dermal Asthenia (HERDA), Equine polysaccharide storage myopathy (called PSSM - polysaccharide storage myopathy - in Paints, Quarter Horses and Appaloosas), Malignant hyperthermia (MH) and Glycogen Branching Enzyme Deficiency (GBED). The influence of Thoroughbred breeding puts some bloodlines at higher risk for Wobbler's syndrome.