Frontotemporal dementia (FTD) is a common cause of dementia in younger people causing impairment in behaviour, language and social functioning. It often runs in families and the genetic form of FTD is usually caused by mutations in one of three genes called progranulin, tau and C9orf72. There are currently no treatments for FTD and we know little about the steps in the disease process. However, there is increasing evidence that there is abnormal inflammation in the brains of people with FTD, particularly in the genetic forms. This study therefore aims to increase our understanding of the role that neuroinflammation plays in FTD by measuring novel markers of inflammation in the spinal fluid of people with genetic FTD. The study will also examine whether there is a relationship between these CSF markers of inflammation and neuroimaging measures of disease severity and progression as well as a novel imaging measure called sodium imaging which may be a surrogate marker for neuroinflammation. Detailed study and identification of such markers will not only be important in understanding the role that neuroinflammation plays in the disease process in FTD, but may also be helpful in guiding development of new treatments for FTD and lead to markers that can be used in clinical trials for monitoring disease progression and response to treatment.