Lethal white overo syndrome

Attention! This is a potentially life-threatening condition for your horse. Time is of the essence, contact your veterinarian immediately.Find a Vet

Lethal White Overo Syndrome

Overo Lethal White Syndrome, Ileocolonic Aganglionosis

Lethal white overo syndrome (LWOS) is an inherited, autosomal congenital condition affecting newborn American Paint Horse foals. It occurs when foals are born homozygous for the lethal white gene. It is the result of breeding two carrier (Overo) horses. LWOS foals are born completely white with blue eyes. Foals are born with ileocolonic aganglionosis, which results in colon dysmotility, colic and ultimately fatal.


Born white w/ white eyes
Colic signs within 4-24 hrs of birth
Minimal fecal production


  • History
  • Clinical signs
  • Physical exam
  • Genetic test



There is no treatment available


Scientific Research

General Overviews

Age Range

Affects newborn foals

Risk Factors