C9orf72 and frontotemporal dementia: C9orf72 is believed to be involved in the regulation of autophagy, vesicular transport and inflammation.6 As a possible pathomechanism, both a loss of function and a toxic gain of function by accumulation of RNA foci or dipeptide repeat proteins are discussed.7,8 Of note, C9orf72 mutations are not only the most common known genetic cause for the development of amyotrophic lateral sclerosis, but also for frontotemporal dementia (FTD) in Europe and North America.3,7,9