Its not clear to me what members of his family have ALS, you mention his sister had it, but this alone would not qualify it as familial. To be familial a clear family inheritance pattern must be demonstrated over at least one generation, or else a demonstration of the genetic defect (which is not readily available at this time)
While familial ALS is 'dominantly' inherited, not all dominant genes get transmitted in the direct fashion to give the 50% figure, this is known as 'reduced penetrance'
In any case it would be highly unusual to present at such a late age, especially if familial. Pain in the buttock would also not suggest ALS, but may be suggestive of a localized soft tissue problem, peripheral vascular disease, sciatica or lumbar stensosis. A pinched nerve can cause an abnormal reflex in the leg. ALS is a motor system problem, although for reasons we dont understand some patients do have sensory symptoms, but this is rare.
It started with his father as far as we know. Out of 7 of his children, 3 have inherited the disorder. One sister is the 72 year old I mentioned, another sister died of it in her 40's, and the other sister is currently not sick but we know she's a carrier because 2 of HER sons are both afflicted in their 40's. She's currently ok (knock wood) but it's probably only a matter of time :(
The sister that recently died at 72 began her symtoms at 71 - she went fast. It comforted me a bit when you said it's rare for familial onset symptoms to start this late, but then again she was 71 when it hit. I'm just so concerned because this is my husband's family, and if his father is ok chances are he'll be ok too.
So far that's a total of 6 people (the dad was the 1st generation, 3 daughters of his for the 2nd generation, and 2 males of the 3rd generation). They say ALS strikes 1 or 2 out of every 100,000. Why can't we have these odds with the lottery?
I forgot to mention that he HAS had sciatica before, which cleared up on its own.
Also, his circulatory problems are thought to be possibly damage from radiation exposure from bomb testing during the Korean war.