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Biology and Genetics - Alzheimer’s Disease Risk Factors and Public Health

Alzheimer’s disease (AD) is a chronic debilitating neurological condition causing gradual but unstoppable cognitive decline. It has become a major public health problem worldwide, emphasizing the immediate need for interventions to prevent the disease or delay its onset.

Alzheimer’s disease is the eighth leading cause of death in people 65 years of age and older, affecting approximately 20–30 million people worldwide.  Alzheimer’s disease is a slowly progressive disorder causing damage to episodic memory; instrumental signs include aphasia, apraxia, and agnosia, together with general cognitive symptoms, such as impaired judgment, decision-making, and orientation. These characteristic symptoms were first described by a German physician, Alois Alzheimer in the early part of the 20th century.  The two essential neuropathologic features of Alzheimer's disease, intracellular neurofibrillary tangles (NFT) and extracellular senile plaques (SP), are defined by a consensus as mandatory for establishing the Alzheimer’s disease diagnosis. These lesions seem to increase at different rates from age at onset and develop over a long period.

Alzheimer’s disease is a heterogeneous disorder with both familial and sporadic forms. Familial Alzheimer’s disease is an autosomal dominant disorder with onset before age 65 years. The first mutation causing the familial form of the disease was identified in the amyloid precursor protein (APP) gene on chromosomes 1, 4 and 21. The APOE ε4 allele has been estimated to account for most of the genetic risk in sporadic Alzheimer’s disease and will further be discussed in the section entitled hazard identification. However, a number of risk factors, such as diabetes mellitus and cholesterol in middle age, are now known to be associated with Alzheimer’s disease. In addition, the presence of the APOE ε4 (Apolipoprotein E) allele is a major genetic risk factor for the disease. Furthermore, social isolation, as shown by objective factors such as having a small social network, being unmarried, not participating in many activities with family and friends, or a mixture of these factors, has been linked with increased risk of Alzheimer’s disease and cognitive decline in many prospective studies.

Determining preventative strategies is critical to the development of effective interventions for Alzheimer’s disease. Taking part in physical activities, visiting family and friends, reading, or watching television involve automatic processes and attention control. From a preventive point of view, it could be that these highly socially networked activities stimulate, and thus help to protect, cognitive abilities and, therefore, delay the onset of Alzheimer’s disease.

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Contributors:  Jelena Ivanovic

Last Reviewed:  June 12, 2012


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