Color: Frame overo white color pattern
Samples Accepted: Blood, Hair
Locus Information: O series
The mutation causing the frame overo white color pattern is also responsible for intestinal development; homozygous foals (those with two copies of the mutation) die soon after birth (Over lethal white syndrome, OLWS).
Test Information: This test is based on a mutation in the EDNRB gene. The frame overo color pattern is autosomal dominant, as any animal with one copy of the allele may have the pattern. A foal with two copies of the gene will be all or nearly all white, have an incompletely developed intestine and die of the autosomal recessive disease known as Overo Lethal White Syndrome (OLWS).
It is possible for the frame overo pattern to be minimally expressed (little or no white markings), or to be obscured by other patterns. For this reason, all horses with the possibility of having frame overo should be tested before breeding (Quarter Horses, Paints, or other breeds in which frame is found, such as a select number of thoroughbred lines). If you have any questions about if your horse should be tested, contact us for specific recommendations.
Metallinos, DL; Bowling AT; Rine J (June 1998). “A missense mutation in the endothelin-B receptor gene is associated with Lethal White Foal Syndrome: an equine version of Hirschsprung Disease”. Mammalian Genome 9 (6): 426–31 Abstract
Further information is available at the Online Mendelian Inheritance in Animals website.