Interesting re: if genetic. I still can't get my head around the entire HYPP population tracing back to Impressive. That discovery happened when I was a little kid and the idea that this beautiful, gleaming halter stallion was the reason for so much disease was, and is, staggering to me.
But for PPID: are there certain breeds over-represented? And certain lines in these breeds? My PPID is a grade PMU mare from Canada.
Is the cause hubandry? Pharmaceuticals used throughout a horse's life? Fly sprays? Vaccines?
Certain feedstuffs? Or lack of anti-oxidants?
Or is it just the "old age cancer" that each species tends to have over-represented in their geriatric populations (dogs = hepatic/splenic hemangiosarcoma; cats = GI lymphoma; horses = benign pituitary cancer)?
Interesting stuff. Wouldn't it be cool if our generation witnessed the arrival of the answer?