Funny you should say that Cozie. I did extensive research on Devons, and they originate from one cat, Kirlee, born to a farm (working) cat in the 1960s, the suspected sire being a feral who had a ringletted coat and lived in a local tin-mine.
It's a theory that the radiation from the tin mines caused the curly hair mutation. They decided to keep Kirlee as a house pet, because he was so loving and affectionate. However, Cornish Rex came into being at the same time, (tin mines again), and she sold Kirlee
. When mated with Cornish, they produced straight haired offspring because the curly haired gene wasn't the same.
They can be susceptible to luxating patella (Little M doesn't, you should see him leap and climb), possibly because of their bull-dog shaped stance, making the front legs appear shorter than the back legs. But extensive out-crossing to certain breeds of cats has widened the gene pool immensely.
I adopted him after doing A LOT of research, and personally think he's part cat, part pixie, with a bit of alien thrown in. 
I couldn't adopt a kitten that I knew couldn't jump or be in pain. I think Manx cats have a form of spina bifida, meaning Manx to Manx matings are at best unsuccessful, at worst result in kits that don't survive.