Cause of Alzheimer’s disease
The cause of Alzheimer’s disease is a question researchers are still trying to answer, but here we discuss some of the factors that may contribute.
Alzheimer’s disease (AD) was first described by Alois Alzheimer when he demonstrated increased amyloid plaques made up of amyloid beta 42 peptide (Aβ42) and neurofibrillary tangles composed of nerve cell associated protein TAU in individuals suffering from dementia.
Aβ42 and TAU proteins are quantifiable biomarkers used in diagnosing AD whereby decreased Aβ42 and increased TAU levels in the cerebrospinal fluid (CSF) are pathognomonic of AD.
Decreased Aβ42 levels in CSF have been noted in elderly people with early AD, which is also referred to as mild cognitive impairment amnestic AD. A rise in TAU levels in CSF generally followed the decline in Aβ42 in the affected patients. Thus, it has been postulated that a chronic imbalance between Aβ42 production and clearance in the brain may be a cause of Alzheimer’s disease.
Genetic mutations and autosomal dominant inheritance patterns have been demonstrated in patients with early onset Alzheimer’s disease (inherited), unlike late onset (sporadic) AD and this supports the Aβ42 hypothesis.
Family history of the disease and presence of amyloid precursor protein (APP) and presenilin (PSEN) genes have been shown in less than one percent of AD cases.
Natural history of AD
Altered metabolism within the brain and subtle and periodic impairments of verbal memory begin a decade or two before AD symptoms. Therefore individuals destined to develop AD have detectable molecular and tissue abnormalities long before overt clinical symptoms appear.
Brain alterations occur well before AD or dementia can be diagnosed and drug interventions directed at the mild-to-moderate clinical stage may be too late to improve symptoms.
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