Overo Lethal White Syndrome is the result of an embryo that is homozygous for the Overo gene. A single Overo gene creates the very striking and popular Overo pinto pattern, but when doubled up, the foal's intestinal system does not develop properly, and the foal dies within 72 hours of birth, when it is unable to digest its first meals.
A Lethal White is a pure white (or almost pure - some have color on the tips of the ears and around the mouth) foal born of two parents both carrying the Frame Overo gene. Most Lethal White foals die within 72 hours of birth, as they lack functional intestinal systems. The gene in homozygous form interferes with the development of the proper nerve function in the lower colon, and the food is unable to be 'moved on.' Sometimes the colon is not even connected completely. To date, there is no surgery or other treatment to save these unfortunate foals.
Mary Ann, this is the most popular coat pattern on paints. The major reason being the difficulty in producing it with the genes available, and not falling right into a pile of Lethal white genes. I wish I had a picture to show you, of one of these beautiful, snow white babies, but I don't.
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6 comments:
Wade, how unfortunate that these beautiful babies are so severely defective.
Mary Ann
Mary Ann,
Not really, as it stops other defective genes, associated with it from propagating into something else. Don't forget along with the beautiful white color of a tiger, come a myriad of junk, some of which should have in all likelyhood not been allowed to reproduce.
Wade
Wade, I have previously mentioned that the white coat in domestic cats is dominant, and they are not without potential problems. "Extreme care is needed when breeding white cats, whatever the breed, because a small proportion of white cats are deaf. This is related to the absence of pigment in the hair, because the inner ear of the cat also contains hairs that vibrate when sound waves enter the ear. If the pigment is missing from these hairs they are not stiff enough to be set in motion. As a result, the sound signal is not passed on to the auditory nerve and therefore never reaches the brain. Fortunately, most white cats still do have pigment in the hairs in the inner ear. It is highly inadvisable to breed from two white cats because the risk of deaf offspring is very considerable - and obviously no one should breed from deaf cats."
From the Cat Encyclopedia
Mary Ann
Wade, also with regard to white domestic cats, I have heard that the blue-eyed ones are more prone to deafness than those of other eye colors. In the case of odd-eyed cats (one blue eye and one gold or green eye), it often happens that the cat is only dear in one ear, the ear that is on the same side as the blue eye.
Mary Ann
Wade, is there such a thing as a dominant white coat in horses, and are there any problems associated with it?
Mary Ann
Mary Ann,
That's basically what the Lethal White Syndrome is. That's why it is harder to produce the more popular overo coat pattern. Although the homozygous guarantee in tobiano is making that pattern a better option.
But, yes there is a dominant white horse that stays alive. The Anderson Family whom I featured earlier on the Blog has make these horses famous. This "albino" horse is actually not a true albino but instead what the American Albino Horse Club (now known as the White Horse Club) calls Dominant White. A Dominant White can be any horse, Quarter, Arabian, Standardbred, etc., that has a white coat with pink skin and dark eyes - black, brown, or blue. A true albino would, of course, have pink eyes, meaning the Dominant White actually carries off-color genes. Given the WHC's immaculate records, breeding for this particular horse has become an almost exact science. Even still, the qualification of dark eyes requires parents who carry genes for off-color coats, thereby creating a 5 percent chance that the off-spring will carry some off-color. (Psst, Mary Ann, off-color is a gentle way to say creme, cremello, champagne.)
Wade
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