BASICS
LWFS (ileocecocolonic aganglionosis) is a fatal heritable syndrome of horses with white patterning occurring most frequently in foals of overo–overo Paint crosses. Failure of proper development of neural crest-derived cells results in a lack of dermal melanocytes and myenteric ganglion cells in the caudal GI tract. Affected foals are completely white (or almost so) and show signs of colic within 24 h of birth. The syndrome is inherited as an autosomal recessive trait and is invariably fatal. A genetic test is available to identify heterozygous carriers.
- Neonatal foals of overo–overo American Paint Horse cross-breeding
- Signs of colic usually noted by 12–24 h of age
- White coloration
- No sex predisposition
- White color, often with blue eyes
- Typically normal, vigorous foals that stand and nurse
- Failure to pass meconium
- Progressive signs of colic noted within 12–24 h of birth (exacerbated with enteral feeding)
- Progressive abdominal distention
- Death within 48–72 h of birth
- May also have congenital deafness
- LWFS is caused by a mutation in the EDNRB gene, which results in problems with migration of neural crest-derived cells, particularly melanocytes and the cells of many autonomic ganglia. Failure of neural crest cells to migrate and mature properly results in the characteristic phenotype (a nonpigmented foal with functional ileus due to an abnormal enteric nervous system)
- Affected foals are homozygous for the mutation, while their parents are heterozygous. The gene is likely involved, or linked closely, with white patterning and deafness in horses. The heterozygous carrier state appears to be highest among overo Paint horses, especially frame overos
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MISCELLANEOUS