not diagnosed

[mummyto2]

Hi, bit of background, my partner had perthes, diagnosed at 2 and a half, this was 40 years ago, so had broomstick plasters, calipers which went on until he was 7. No problems since, in fact he has ran 4 London marathons in his 30's to prove to himself he is now fine! Our son is just about to turn 3years old and has on and off for the last 2 weeks complained of knee pain, although he is the sort of child who always has something wrong!! I think i may have noticed a slight limp, again not constant by any means, he is also waking in the night, upset, appearing in pain but cannot say what is wrong. I initially assumed this was growing pains, especially as we asked when he was born if perthes was passed on in families and we were told no. I have read on many sites that it appears it does run in some families. I am obviously going to take our son to see the GP, but didn't want to get fobbed off, so in a nut shell ( sorry- Ive rambled on!) what should i be pushing for? what is the evidence of this being hereditary? and any other advice greatly received.
thank you Emma