Lethal White Overo (LWO)
LWO, Frame Overo White Spotting Pattern
Lethal White Overo (LWO) is a lethal genetic disorder that is also associated with the frame overo white spotting pattern. A foal that inherits two copies of the mutation will suffer intestinal abnormalities caused by undeveloped nerves in the digestive system and these animals typically die within a few days after being born. These foals are also typically born almost pure white. A foal that inherits one copy of the mutation will exhibit the frame overo spotting pattern that can vary along a continuum from a horse with minimal white spotting to horses with lots of white coloring. This color pattern is said to “frame in the horse” with white coloring occurring primarily on the abdomen, middle of the neck, and on the face. It is important to note that some horses that carry one copy of the mutation may have a slight or undetectable white spotting pattern.
Reading Your Results
A. (CLEAR/NORMAL):
These horses have two copies of the normal gene and will neither develop Lethal White Overo or a frame overo white spotting pattern nor pass this mutation to their offspring.
B. (CARRIER/NOT AFFECTED):
These horses have one copy of the normal gene and one copy of the mutation associated with this disease. They will develop frame overo white spotting but not Lehtal White Overo which typically results in white spotting on the abdomen, neck, and face and will, if bred, pass the mutation to 50% of its offspring, on average.
C. (AT RISK/AFFECTED):
These horses have two copies of the mutation associated with Lethal White Overo which typically results in a foal born with intestinal abnormalities leading to death.
Additional Details
Inheritances
Autosomal Incompletely Dominant
Affected gene
EDNRB
Chromosome
Ch. 17
Mutation
c.353-354 TC>AG; p.I118K
Publication:
Metallinos DL, Bowling AT, Rine J. A missense mutation in the endothelin-B receptor gene is associated with Lethal White Foal Syndrome: an equine version of Hirschsprung disease. Mamm Genome. 1998;9(6):426-431. [PubMed: 9585428].
