FUS and amyotrophic lateral sclerosis: The Mendelian gene variants causing ALS are associated with a younger age of onset.9De novo mutations in FUS and SOD1 have been found to be an additional cause of apparently sporadic disease.10,11 As genetic therapies are now being developed, and because about 15% of people with apparently sporadic ALS carry a Mendelian gene variant,12 genetic testing is likely to become more frequent regardless of family history.