Lavender Foal Syndrome or Coat Color Dilution Lethal is a genetic disorder that generally affects Arabian horses (most often from Egyptian lines). It's a neurological disorder that causes "tetanic" episodes (a form of seizure) and a complete inability to stand. The foal may struggle and "paddle" with its hooves, but is unable to even get into an upright position.
The name of the syndrome comes from an associated color dilution, that lightens the coat to lavender or pink. However, the dilution may be minor or absent.
Affected foals are generally euthanized.
(This is a good example of how you could put together a specific disorder associated with a breed - the bizarre combination of a weird coat color and inability to stand sounds like something out of fiction, doesn't it).
Picture courtesy of PLOS Genetics and Dr. Yael Giora.