Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurodegenerative disease of upper and lower motor neurons which often results in death from respiratory failure within 2-4 years. It has been estimated that 5-10% of ALS patients have a family history with ALS. The genetic background of the disorder is heterogeneous, and recently molecular genetic testing has become increasingly relevant, also in the clinical evaluation. As several genes have been identified in which the pathogenic mutations are characterized by reduced age-dependent penetrance, genetic testing can be relevant to consider, also in isolated cases.