Epidemiology and etiology of Alzheimer's disease: from genetic to non-genetic factors.

At present, the etiology of Alzheimer's disease (AD) is still unclear, but both genetic and non-genetic factors are thought to take part in the etiopathogenesis of AD. Epidemiologic researches revealed that genetic factors played a decisive role in the development of both early-onset AD (EOAD) and late-onset AD (LOAD). The mutations in APP, PSEN1 and PSEN2 are inherited in a Mendelian fashion and directly lead to the EOAD, while recent genome-wide association studies have identified numbers of risky genes, which influences the susceptibility to LOAD. Although genetic factors are inherited and fixed, non-genetic factors, such as occupational exposures (exposure to pesticides, electromagnetic fields, organic solvents and volatile anesthetics), pre-existing medical conditions (cerebrovascular disease, hypertension, diabetes, dyslipidemia, traumatic brain injury, depression and cancer) and lifestyle factors (smoking, consumptions of alcohol and coffee, body mass index, physical activity and cognitive activity), are partly environmentally-determined. Timely interventions targeted at these non-genetic risk factors may offer opportunities for prevention and treatment of AD. In the future, more high-quality and large-sample epidemiologic studies are needed to identify risk factors for AD, and the interaction models between genetic and non-genetic risk factors required further investigation. In addition, public health campaigns targeted at modification of non-genetic risk factors should be developed among population at high risk of AD.