Both Alzheimer’s disease (AD) and frontotemporal dementia (FTD) are genetically complex and heterogeneous disorders. Although fully penetrant (causal) mutations leading to predominantly familial early onset AD have been identified in three genes (APP, PSEN1, and PSEN2), they only account for a small fraction of AD patients. PSEN1 is considered the most frequently mutated gene in early onset AD. Mutations in the microtubule-associated protein tau (MAPT) gene have been reported in up to 50% of hereditary cases of FTD. One partially penetrant genetic risk factor (APOE4) has been established for the more common late-onset form of AD. Despite advances in elucidating the genetic epidemiology of AD and FTD, the etiology for most patients with dementia remains unclear.
Key words: Alzheimer’s disease, frontotemporal dementia, genetics, linkage, mutation.