Severe Combined Immunodeficiency Disease (SCID) in Arabian horses is a recessively inherited disorder that results in affected foals being born without a working immune system. These foals typically die of an infection, such as pneumonia, within the first half year of life. SCID is caused by a defective PRKDC gene (previously known as DNA-PK(CS)).
Affected foals appear normal at birth. By about 10 days of age, they will develop symptoms of a range of infections, such as bronchopneumonia, diarrhea, colic or lameness.