There is a wide body of literature on the genetics of ALS. In brief, about
10-15% of ALS cases appeare to be familial, and a subset of these appear
to be inherited as an autosomal dominant trait. One gene for ALS has
already been found. Mutations in the SOD1 gene have been found to cause
ALS in about 30% of the autosomal dominant families. Searches for the
other autosomal dominant gene(s) are underway. In addition, one gene for
an autosomal recessive form has been localized to chromosome 2, but not yet
cloned.
Hope that helps.
Jonathan Haines