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Living with Dementia

Alzheimer’s Disease Risk Factors

  • - Dementia News
  • Aug 21, 2011
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  • Viewed: 2645
Tags: | ad risk factors | amyloid plaques | amyloid protein | aphasia |

Age
Age is a risk factor for AD. The prevalence of AD doubles every five years after the age of 60.

Family history

A family history of AD is a consistent risk factor, and represents around a fourfold increase in the risk of developing the disease. It is thought that as many as 33% of all cases of AD may be familial.

A link has been established between the frequency of a specific allele, apolipoprotein E4 (ApoE4), and the occurrence of AD. The presence of the ApoE4 allele increases the probability that the patient with dementia has AD. The absence of the ApoE4 allele makes this less likely. Although there is a strong link between ApoE4 and AD, not everyone who carries the allele develops AD. Conversely, not all AD patients carry the allele. So despite the fact that ApoE4 is a risk factor for AD in some patients, it is not suitable for routine use as a diagnostic marker for AD.

Other risk factors

Gender appears to be a risk factor, women being at greater risk of developing AD than men. The higher prevalence of AD among women is probably due to a longer life expectancy. Repeated head trauma also increases the risk of developing AD. The presence of vascular disease is a potential risk factor. All individuals with Down’s syndrome develop the characteristic neuropathological features of AD by the age of 40, although many do not demonstrate the clinical symptoms of dementia.

Neuropathology of AD

The most characteristic neuropathological features (Table 5) are amyloid (senile) plaques and neurofibrillary tangles (NFTs). Amyloid protein is believed to play an important role in the pathogenesis of AD and may be critical for the formation of the amyloid or senile plaques in the brain. These plaques seem to reflect damage in the surrounding nerve endings. This damage to the neurons causes impaired neurotransmission and results in the cognitive deficits observed with AD.

Although NFTs are also a characteristic finding in the brain they are not specific to AD and are found in several other degenerative dementing disorders. NFTs contain paired helical filaments (PHFs) which are composed of abnormal microtubule-associated proteins (tau protein). In AD, abnormal phosphorylation of the tau protein results in aggregation of PHFs to form the NFTs. The definite diagnosis of AD relies on the presence of sufficient numbers of both amyloid plaques and NFTs at autopsy or via biopsy.

NEUROPATHOLOGICAL FEATURES

  * Neurofibrillary tangles
  * Senile (amyloid) plaques
  * Neuronal loss
  * Cortical and central atrophy

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