Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two devastating adult-onset neurodegenerative disorders. No cure exists for these diseases. Ten percent of ALS patients suffer from a familial form of the disease, while FTD is caused in 40% of patients by a genetic defect. In 2011, the most important genetic cause of ALS and FTD was discovered. The causative mutation was a repetition of a piece of non-coding DNA, a so called tandem repeat, in a gene with an unknown function, named C9orf72. A team of scientists has now discovered that proteins translated from this tandem repeat interfere with the nucleocytoplasmic transport which they found is essential for causing ALS and FTD.