Alzheimers Disease - Research Paper Example

? Alzheimer’s disease: Is it Hereditary Explanation of Alzheimer’s disease According to Rabins , Alzheimer’s disease (AD) “is a progressive disorder of the brain, which “is characterized by a gradual deterioration of mental faculties caused by loss of nerve cells and the connections between them”. AD is the most common form of dementia constituting 50% to 70% of dementia cases. Changes in behavior and personality are associated with AD. AD follows a reasonably well predictable and relentless course in an individual with the disease. Yet, the decline in mental faculties does not follow a similar pattern, and varies from individual to individual. Findings from recent studies have, however, shown that only 50% of individuals diagnosed with AD can look forward to a survival rate of over five years from the time of diagnosis of AD. Among the remaining 50% cases, survival of more than 20 years has been reported (Rabins, 2010). Initial symptoms of AD present themselves, in most cases, in the later stages of life of sixty years and above. Estimates on the prevalence suggest that approximately 5.1 million Americans have AD (National Institute on Aging, 2011). There is lack of clarity on the origin and start of the disease processes of AD. It is generally assumed that presentation of the problems associated with AD occurs almost ten years after the actual damage has occurred to the brain. Abnormal protein deposits from amyloid plaques and tau tangles occur all over the brain, resulting in damage to neurons, which lose their efficiency to function, and gradually die. Among the parts of the brain affected early is the hippocampus, a vital constituent in memory formation. Progressively, the damage spreads to all parts of the brain, and in the final stages of AD, widespread damage of the neurons causes significant shrinkage of brain tissue (National Institute on Aging, 2011). In the first stage of the disease, the symptoms are mild in the form of impaired short term memory, faulty judgment, and poor insight. In the second stage the memory deficits become worse. There is also the development of decline in basic self-care skills, delusions, and hallucinations. In the third stage, there is almost total loss of reasoning capacity, and the debilitation becomes so bad that there is total dependence on care from others (National Institute on Aging, 2011). Three factors are associated with cause of AD. These factors are genetic make up, environmental, and lifestyle. Evidence coming out of studies over the last three decades is paving the way of untangling the knotty issue of whether AD is the result of genetic factors, environmental factors, lifestyle factors, or their combination (National Institute on Aging, 2011). Assumptions AD is classified into early-onset AD, where the symptoms of the disease present prior to the age of 60 years and late-onset AD, which presents after the age of 60 years. Early-onset AD accounts for only about 5% of all cases of AD. It is early-onset AD that is believed to be implicated in the hereditary nature of the disease. The inheritance assumption here is in the presence of the inherited abnormal gene on one of the three chromosomes, namely the amyloid precursor protein (APP) gene on chromosome 21, the presenilin-1 (PS-1) gene on chromosome 14, and the presenilin-2 (PS-2) gene on chromosome 14. It is believed that the presence of such inherited genetic mutations is a definite pointer to the development of AD. In the case of late-onset AD, these genetic mutations are believed not to be the culprits in the development of the disease. Instead, genetic predisposition, coupled with other essential environmental risk factors, is considered responsible for the development of the disease. In the absence of the essential risk factors, the disease is unlikely to develop, and this is the reason for individuals with a genetic disposition for AD not developing the disease (Rabins, 2010). The author has not based any of these assumptions on studies conducted in person, but has produced this information on the basis of findings of studies conducted by others and information available on the question of the hereditary nature of AD (Rabins, 2010). Variation in the ApoE4 gene is assumed as the main risk for the development of AD. Those carrying the ApoE4 gene are considered to be at higher risk for AD, because of the connection of AD with neurotransmission channels, oxidative stress, and the effectiveness of estrogens. Such a surmise has given rise to other candidate genes for the development of AD, namely COMT connected with neurotransmission, SOD2 connected with the elimination of oxidative stress, and ESR1 and ESR2 which are estrogen action facilitators (Alzheimer’s Disease: A new way of approaching early detection of Alzheimer’s disease). The article is not a direct study report, but provides a peek into the new direction in research in AD that is being conducted by a researcher (Alzheimer’s Disease, 2012). Over nearly two decades it has been assumed that inherited AD was caused mostly through the mutations of the presenilin genes. It was further assumed that it was over activity of these genes that resulted in AD. However, a study on mice models has demonstrated that it is not over activity, but absence of activity of the presenilin genes that leads to the development of AD (Alzheimer’s Disease, 2004). Support for the assumption of the involvement of both genetic disposition and environmental factors in the development of late-onset AD is given by Goddard et al (2004). It is assumed that the genetic risk factor in late-onset AD is related to the ApoE locus on chromosome 19, and that identifying other genetic factors is not easy due to the heterogeneous nature of the disease. However, there are pointers to the linkage of chromosome 20 also in the development of late-onset AD, and this supports the possibility of other genetic factors being present in the development of AD (Goddard et al, 2004). These findings were the result of a study conducted on 43 elderly sibships, as the test group, taken from the NIMH AD Genetics Initiative, and 129 elderly unrelated control subjects, taken from the Oregon Brain Aging Study (OBAS). To incorporate covariates like age and ApoE genotyping into the analysis, the study used a new statistical approach. The design of the study makes the findings of the study reliable. However, the authors of the study recommend further studies to confirm the findings of the study (Goddard et al, 2004). Hereditary factors and environmental factors have been assumed to play a marked role in the development of AD. To this is the added assumption that the environmental or non-genetic factors are risk factors for AD, and have to be assessed on the basis of relation to the life course. Cognitive function varies over life course, and various sets of influences on cognition will have a significant role to play in the development of AD at different stages in life. Midlife risk factors for AD may not be significant risk factors in later life. For example obesity and high blood pressure constitute environmental risk factors for AD in midlife, but the development of these risk factors in later life may not be that important to onset of AD (Gatz et al, 2010). These assumptions are derived from the study conducted on thirty same-sex twin pairs, all of whom had been assessed at baseline and that one of the twins developed dementia at a later stage in life, at a minimum of three years after the baseline assessment. The limitation of the study pertains to the low sample number of twins. However, the authors claim that rigorous criteria were used in selection of the matched pairs to offset the small sample size limitation (Gatz et al, 2010). Neurological conditions like AD have a strong impact on the ability to recall details of one’s life experiences or episodic memory. It is assumed that episodic memory deficits are inherited. Studying measures of studying and recall, it has been found that there is significant overlap of genetic factors and environmental factors in episodic memory defects. Furthermore, episodic memory defects are more likely to arise from genes that are specific to the acquisition process (Panizzon et al, 2011). The findings mention come from a study that involved a large sample size of 314 monozygotic twin pairs, 259 dizygotic twin pairs, and 47 unpaired twins, from the Vietnam Era Twin Study of Aging. The limitations of this study include the all male nature of the samples, making it difficult to extend the findings to the female gender (Panizzon et al, 2011). Student’s Position I take the position that it is still too early to say that AD is hereditary. There may be many indications that AD is hereditary, but ignoring the contribution of environmental factors will be with the peril of incomplete understanding of the etiology of the disease. Such a position finds support from the lack of full understanding of the genes involved in the development of AD, the manner in which they contribute to it, and the impact of hereditary distortions in their contribution to the development of AD. Studies clearly show that environmental factors do have a role to play in the development of AD (Rabins, 2010; Goddard et al, 2004; Panizzon et al, 2011). The most likely position on the etiology of AD is that hereditary factors have a strong role to play in AD, but environmental factors also contribute to the development of AD. Implications and Future Research The implications of this paper are that there is still no clear understanding on what causes AD. Genetic factors are found to have a strong role to play along with environmental factors. Removing this enigma in the development of AD will require future research to have several components. Future research will have to identify the complete set of genetic factors involved in the development of AD, and the manner in which they contribute to it. In addition, future studies will have to identify the full set of environmental factors that may have a role to play in the development of AD, and the life course at which they contribute to the development of AD. Finally, correlation studies will have to be conducted to provide answers to the interaction between genetic factors and environmental factors in the development of AD. References Alzheimer’s Disease: A new way of approaching early detection of Alzheimer’s disease. (2012). Obesity, Wellness & Fitness Week, (Jan 14, 2012), 44. Alzheimer’s Disease; Deactivation of two genes could b the cause of AD. (2004). Obesity, Wellness & Fitness Week, (Jun 26, 2004), 35. Gatz, M., Reynolds, C. A., Finkel, D., Pedersen, N. L. & Walters, E. (2010). Dementia in Swedish Twins: Predicting Incident Cases. Behavioral Genetics, 40, 768-775. Goddard, K. A. B., Olson, J. M., Payami, H., Van Der Voet, M., Kuivaniemi, H. & Tromp, G. (2004). Evidence of linkage and association on Chromosome 20 for late-onset Alzheimer’s Disease. Neurogenetics, 5, 121-128. National Institute on Aging. (2011). Alzheimer’s Disease Fact sheet. Retrieved March 27, 2012, from, National Institutes of Health Web Site: http://www.nia.nih.gov/alzheimers/publication/alzheimers-disease-fact-sheet. Panizzon, M. S., Lyons, M. J., Jacobsen, K. C., Franz, C. E., Grant, M. D., Eisen, S. A. & Xian, H. (2011). Genetic Architecture of Learning and Delayed Recall: A Twin Study of Episodic Memory. Neuropsychology, 25(4), 488-498. Rabins, P. V. (2010). Alzheimer’s Disease. HopkinsMemory.com. Retrieved March 27, 2012 from www.johnshopkinshealthalerts.com/alerts_index/memory/23-1.html. Read More