C9orf72 and amyotrophic lateral sclerosis: Our studies suggest that several mutations in the dominant genes may be responsible for the disease manifestations since, in our preliminary studies, two dominant genes of TARDBP and FUS were found to be mutated in the ALS patient and not in his healthy identical twin, whereas the healthy identical twin had a mutation of C9orf72 which has been shown to be associated with the familial form of the disease (Table 1).