The Role of Genetics in TBI Recovery
Graham, I.D., Gentleman, S.M., Nicoll, J.A.R., Royston, M.C., McKenzie, J.E., Roberts, G.W., Mrak, R.E., & Griffin, W.S.T. (1999). Is there a genetic basis for the deposition of B-Amyloid after fatal head injury? Cellular and Molecular Neurobiology, 19(1), 19-30.
The etiology of Alzheimer's disease has been unknown for the most part. In some cases, "there is an early onset of the disease and a tendency to run in families, implicating a genetic risk factor"(p.19). Environmental and genetic factors also play a role in the presence of the disease. Previous work has shown an existence of "mutations in the B-amyloid precursor protein gene on chromosome 21 that are causative for Alzheimer's disease" (p.20). In cases of abnormalities on chromosomes, a mis-metabolism of the precursor protein "gives rise to the AB found in diffuse plaques" (p.20).
There is increasing awareness of the environmental factor, more specifically, history of previous head injury playing a role in the etiology of the disease. Support has been derived from "Alzheimer-like pathology in the brains of patients subjected to domestic violence or repeated sub-concussive and concussive blows to the head," including those of boxers with dementia pugilistica (p.20). Data suggests that similar molecular neuropathologies of dementia pugilistica and Alzheimer's disease provide evidence that Alzheimer-like pathology may exist in long-term head injured survivors.
A number of studies tested the hypothesis that head injury is indeed a risk factor for the development of Alzheimer's disease-like pathology. They included full postmortem examinations since 1968 that were carried out over 1000 cases of fatal head injuries. The ages ranged from several weeks to 90 years, with the duration of survival following brain injury ranging from 1 hour to 15 years. Histological studies were undertaken on blocks of the cerebral hemispheres, cerebellum, and brainstem.
Results of the studies revealed molecular similarities between the responses in the brain after head trauma and Alzheimer's disease. "The acute-phase response to head injury involves the up-regulation of microglial IL-1, and neuronal B-APP," and amyloid deposits (all resulting in the plaque buildup around cells) throughout the cortex in individuals with apoE-e4 (p.26). This also occurs in individuals with Alzheimer's. Collectively, the results provide a pathophysiological mechanism for increased risk of Alzheimer's disease following traumatic brain injury.
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