How strongly genetic, if at all, is ALS (amyotrophic lateral sclerosis)?
The simple answer would be that 10% of adult cases of ALS are familial; the rest are sporadic, in that there is no family history. Although a single gene is strongly implicated in ALS, not all cases have any mutation in that gene; other genes in the same pathway may be affected, leading to a similar clinical picture. And even in the familial cases, it is not always the same mutation, so that in some families the disease is inherited recessively, in others dominantly. The sporadic cases probably represent mutations in single individuals, but few have been identified so far.
