Fnord wrote:
In the OP's context, a "Zebra" is an obscure illness, disease or condition affecting a comparatively small number of people, but with symptoms somewhat similar to one or more different and more common illnesses. It is so named because these diseases/conditions are sometimes misdiagnosed by well-meaning (but often inexperienced) doctors when something far more common is actually the cause. Medical students are told "remember, if you hear hoof beats, think horses, not zebras".
Doctor 1: "I think this patient may have Castleman's disease."
Doctor 2: "Castleman's disease is a zebra, there are far more likely causes of his fever and weight loss."
The fictional characters of the TV show "House" were known for "chasing zebras".
The house comparison makes more sense as they had several seasons of different zebras. I was confused because the op asked if anyone had one specific rare disorder instead of asking about any and all rare conditions.