In order to determine the frequency of genetic mutations in the MAPT, GRN and C9ORF72 genes in the Turkish dementia patient population, we used a combination of different sequencing and expansion analyses techniques in a cohort of 95 dementia patients from 93 families, clinically diagnosed mostly with AD (n = 54, 56.8%) or FTD (n = 28, 29.5%). The gene discussed is C9orf72; the disease is dementia.