es (to a lesser degree) are also found to accumulate in the aging of individuals who are not demented, leaving the causes of Alzheimer's a mystery. Research has shown that there are genes that also play a role in this disease and families with a history of Alzheimer's tend to develop symptoms early, prior to the age of 50 years. Those carrying specific forms of the apolipoprotein E, or ApoE gene are at increased risk for developing Alzheimer's, though this does not absolutely predict Alzheimer's disease. Other factors found to be related to Alzheimer's include head injury, education level, and toxins (Epstein & Connor, 1999).
Theories of Alzheimer's Disease and Cognitive Decline
Chan (2002) presented the theory that diagnosis of dementia in Alzheimer's is problematic. This author stated that in the cerebral cortex there are cognitive decline curves that are representative of the rate of attrition for neurons, and normal aging results in one curve while a deviation from this curve represents a cognitive decline. It is hypothesized that those with a higher brain reserve start at a higher percentile of neurons, which affects the rate of decline. This complicates the diagnosis of a neurodegenerative disease, since there are some individuals that may suffer from cognitive declines that are not due to disease.
McDonald (2002) pointed out that there is a debate in the literature regarding the relationship between normal aging and dementia versus dementia due to Alzheimer's disease. This author also presented a theory related to the causes of age-related cognitive decline such as is found in Alzheimer's disease. McDonald stated that this decline is due to various co-factors. Each patient presents with different combinations of these co-factors, which explains the differences in levels of dementia and other symptoms. The co-factors include genes, neurotransmitter changes, vascular abnormalities, stress hormones, head trauma...