Alzheimer's disease (AD), also known simply as Alzheimer's, is a neurodegenerative disease characterized by progressive cognitive deterioration together with declining activities of daily living and neuropsychiatric symptoms or behavioral changes. It is the most common type of dementia.
The most striking early symptom is the loss of memory (amnesia), which usually manifests as minor forgetfulness that becomes steadily more pronounced with illness progression, with relative preservation of older memories. As the disorder progresses, cognitive (intellectual) impairment extends to the domains of language (aphasia), skilled movements (apraxia), recognition (agnosia), and those functions (such as decision-making and planning) closely related to the frontal and temporal lobes of the brain as they become disconnected from the limbic system, reflecting extension of the underlying pathological process. This pathological process consists principally of neuronal loss or atrophy, principally in the temporoparietal cortex, but also in the frontal cortex, together with an inflammatory response to the deposition of amyloid plaques and neurofibrillary tangles.
The ultimate cause of the disease is unknown. Genetic factors are known to be important, and dominant mutations in three different genes have been identified that account for a much smaller number of cases of familial, early-onset AD. For the more common form of late onset AD (LOAD), ApoE is the only repeatibly confirmed susceptibility genes for AD. In 2007, evidence suggested a possible association between SORL1 alleles and late onset of AD.