Genetic studies have led to major discoveries in the pathogenesis of various neurodegenerative diseases. Ubiquitin-positive familial frontotemporal dementia was recently found to be caused by mutations in the progranulin gene (PGRN), and the major constituent of the inclusions, TDP-43, was subsequently identified. The tau gene (MAPT) causes frontotemporal dementia with parkinsonism linked to chromosome 17. In Parkinson disease, LRRK2 mutations have emerged as a major cause of both familial and sporadic forms, adding to the previously known genes SNCA,PRKN,DJ1 and PINK1. Several genes have been implicated in Alzheimer disease, including the APP gene and the PSEN genes. Recently, variants in the sortilin-related receptor 1 gene, SORL1, were associated with Alzheimer disease.