As pertaining to the difficulties with finding the right diagnosis, even postmortem, in patients (formerly, professionally) playing high contact sports with ALS like symptoms (and other brain-related ailments) perhaps this particular episode from Neuroscene might prove to be illuminating:

http://www.podcastdirectory.com/podshows/2350604

And one dealing with ALS research:
http://www.podcastdirectory.com/podshows/7087678

Over 90% of cases of ALS are sporadic, meaning they do not have a [single] genetic cause. The vast majority of familial ALS cases have been linked to a gene by now, with the plurality belonging to mutations on the gene SOD-1, though aberrant SOD-1 activity doesn’t appear to be the cause in sporadic ALS, the majority of cases. So, no, by and large, ALS is not genetic. If it were we’d know what causes it other than in very non-specific terms and we’d better be able to treat it. There are any number of theories as to what causes ALS. What the OP was getting at, I believe, was that Lou Gehrig didn’t have ALS but rather a similar disease releated to physical trauma of the CNS that falls into the same family of diseases as ALS called Motor Neurone Diseases. As he said, clinical distinction of these diseases is often quite difficult and post-mortem pathology analysis of tissue is really needed to confirm, which, in the case of Gehrig himself, is not possible.

:0 HIV or STD? What led you to that conclusion? The story discusses repeated head trauma. How is that related to HIV?
Wow.

Yes, by definition Lou Gehrig had Lou Gehrig’s disease. Because it was his.

/End Morbid humor