SCID is Severe Combined Immunodeficiency. It's a defect found in Arabians (and horses with a lot of Arabian breeding). The foals appear normal as long as they get colostrum, but later prove to have no immune system, for all intents and purposes (they are unable to produce key white cells). They usually don't survive more than, at most, six months. The symptoms initially resemble any one of the minor infections common in foals, and conclusive diagnosis requires blood tests.
SCID is a recessive defect and there's now a genetic test to detect carriers. So, it's possible to avoid by not breeding two carriers together.
There's no treatment, let alone cure.
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