Frame overo/lethal white syndrome (OLWS)
Frame overo markings include eye-catching white patches, and often a white face accompanied by one or two blue eyes. The amount of white on a frame overo horse or pony can be highly variable, from a couple of white hairs all the way up to majority white coat colours.
Frame overo is unique among white coat colour patterns in that foals born with two copies of the frame overo gene suffer from the heart-breaking and fatal Overo Lethal White Syndrome (OLWS). Testing helps breeders avoid crosses that could produce Lethal White Syndrome foals.
Gene or region and technical reference
n. Test developed using animal controls.
Ovr. Test developed using animal cases.
Frame overo horses often have distinctive white markings. They can also have one or more partially or completely blue eyes.