A goal of genetic research is to identify risk factor loci for complex disorders, and to understand a molecular mechanism of the factor on development of the disease. Dementia is the most common neurodegererative disorder in the elderly. Three frequent neurodegererative dementias are Alzheimer disease, dementia with Lewy bodies, and frontotemporal lobar degeneration, characterized by senile plaque with amyloid beta and neurofibrillary tangles with tau, Lewy body with alpha-synuclein, tau or tau-negative ubiquitin-immunoreactive neuronal inclusions with TDP-43, respectively. Overlapping symptoms, progress and neuropathological findings often complicate the diagnosis. Genetic risk factors obtained by genome-wide association study might provide new insight into etiology common to dementia.