Neuropsychological and Genetic Factors Surrounding Alzheimer's Disease Alzheimer's disease is a debilitating illness that interferes with an individual's ability to recall short-term and long-term memory. People diagnosed with the disease can initially recall recent activities though they have difficulties with long-term memory. However, these patients have difficulties with short- and long-term memory over time as the disease develops. Given the increase in the number of people diagnosed with this condition, Alzheimer's disease is regarded as the most common type of dementia among the elderly. This clinical condition is basically caused by neurodegeneration and surrounded by a progressive decline in mental ability as well as difficulties in independent living. This paper focuses on examining the neuropsychological and genetic factors surrounding the illness, early signs of the disease, and possible cures to the debilitating disease.

Brief History of Alzheimer's Disease

Alzheimer's disease has a history that can be traced back to over 100 years ago when Alois Alzheimer, a German physician, conducted a grim postmortem analysis of one of his patient's dementia-ravaged brain. When conducting this analysis, Alzheimer hoped to expose the biological roots of the patient's rapid and severe mental deterioration and unusual mood swings (Marsa, 2015, p.54). The patient was surrounded in a fog of confusion, displayed delusional behavior, and would occasionally become wild and uncontrollable. During the examination, Alzheimer noticed that small clumps of hard bundles of protein known as amyloid plaques were cuddled up next to the labyrinth circuitry of healthy nerve cells. Moreover, many fibers extending from the healthy nerve cells were not only tangled but also thickened. Therefore, the main features of characteristics of Alzheimer's disease are the amyloid plaques and tau tangles in the brain circuitry. Since then, scientists and physicians have focused on identifying how the proteins work and their role in the aberrant brain circuitry.

Since discovery, Alzheimer's disease has become a major public health issue that is considered as one of the most common form of dementia across the globe because it is a progressive neurodegenerative disease that affects many people, especially the elderly. The disease affects more than 20% of people aged 80 years and above and is estimated to affect more than 35 million people worldwide by 2050 (Femminella, Ferrara & Rengo, 2015, p.1). As a result of this projection, Alzheimer's disease is increasingly likely to generate a significant economic and social burden.

Genetic Factors Surrounding Alzheimer's Disease

The causes of Alzheimer's disease are not yet fully understood by scientists though increased examination or study of the disease shows that genes play a significant role in its development. Alzheimer's disease is an example of an inherited genetic illness, which is sometimes caused by a genetic mutation or permanent change in some genes. If an individual inherits a genetic mutation that causes Alzheimer's disease from his/her parent, he/she is increasingly likely to get the disease. However, this disease may be caused by the occurrence of a genetic variant, especially when the variant increases disease risk and directly causes the disease or disorder.

Prior to the era of gene identification, there were several clinical observations that demonstrated that Alzheimer's disease has a genetic component. One of these observations is family history, which is regarded as a major risk factor for the disease. In addition to age, family history is the only risk factor that has been consistently recognized in epidemiological studies. In this case, the existence of an affected first-degree relative is linked with an estimated fourfold increased risk for Alzheimer's disease (Levy-Lahad & Bird, 1996, p.829). According to the findings of several studies, lifetime risk for first-degree relatives was close to 50%. This is an indication that genes with autosomal dominant inheritance are major risk factors for a significant portion of Alzheimer's disease. The second clinical observation showing the link between the disease and genetic component is that Alzheimer's disease and dementia is closely associated with Down syndrome i.e. trisomy 21. Individuals with Down syndrome tend to invariably develop the neuropathology attribute of Alzheimer's disease by 40 years. This implies that the individuals have an enhanced incidence of clinical dementia, which in turn implicates chromosome 21 genes in the pathogenesis of Alzheimer's disease. The third observation is that in some families, the disease isolates as an autosomal dominant characteristic over several generations. This observation contributed to the hypothesis that a single gene's mutation could be enough to generate Alzheimer's disease that was similar to the disease in the general population. Therefore, genes responsible for familial Alzheimer's disease are seemingly relevant to those responsible for non-familial types of Alzheimer's disease.

These factors contribute to the loss of connections between nerve cells and the eventual death of these nerve cells in the brain circuitry. Generally, there are two kinds of Alzheimer's disease with varying genetic components i.e. early-onset and late-onset. The causative genes of both types of Alzheimer's disease are amyloid precursor protein, apolipoprotein F, STM-2/PS-2, and S182/PS-1 gene on chromosome (Levy-Lahad & Bord, 1996, p.829).
Early-onset Alzheimer's disease affects individuals between 30 and 60 years, which represents less than 5% of Alzheimer's patients ("Alzheimer's Disease Genetics Fact Sheet," 2015). Some of the early-onset Alzheimer's diseases are brought by unknown causes but most of them are inherited and known as familial Alzheimer's disease. This type of the disease is caused by any different single-gene mutations on several chromosomes i.e. 1, 14, and 21. Each of the single-gene mutations results in the formation of abnormal proteins, which become causes of the disease. While gene mutations on chromosome 21 result in the creation of abnormal amyloid precursor protein, those on chromosome 14 generate abnormal presenilin 1 and mutations on chromosome 1 contributes to abnormal presenilin 2. Scientists have stated that each of the single-gene mutations play a part in breakdown of APP, a protein whose exact function is currently unknown. The breakdown of this protein is part of a procedure that creates harmful forms of amyloid plaques, which is a major factor in development and growth of Alzheimer's disease.

Late-onset Alzheimer's disease is the most common type of the disease which develops from age 60 and above. While the causes of this type of Alzheimer's disease are not yet fully understood, it is commonly attributed to genetic, lifestyle, and environmental factors that enhances the risk of an individual to develop the disease. Single gene-mutations that are responsible for early-onset of the disease are not seemingly involved in late-onset Alzheimer's disease. Clinical researchers and scientists are yet to identify a particular gene that generates this type of Alzheimer's disease. Nonetheless, an individual's risk of developing this disease is increased by one genetic risk factor i.e. apolipoprotein E. gene that is found in chromosome 19. The recent genome-wide screening technologies show that apolipoprotein E. is the single most significant genetic risk factor in late-onset Alzheimer's disease (Bertram & Tanzi, 2012, p.87). The most common form of apolipoprotein that is a major risk factor in development of late-onset Alzheimer's disease is APOE ?4. Apart from APOE ?4, researchers have found that BIN1, CR1, CLU, and PICALM are other genes that enhance an individual's risk to develop late-onset Alzheimer's disease.

Neuropsychological Factors Surrounding Alzheimer's Disease

Neuropsychological factors surrounding Alzheimer's disease are related to the concept of reserve which has been suggested to cause the disconnection between the extent of brain damage or pathology and its clinical symptoms (Sobral, Pestana & Paul, 2015, p.39). The two kinds of reserve that reportedly generate autonomous and interactive contributions to preserving function in brain injury. Cognitive reserve is a concept that refers to the ability of an individual to flexibly and efficiently use available brain reserve. This concept has largely been used to inform cognitive aging and describe the ability of the adult brain to cope with the impact of neurodegenerative process.

Individuals with a lower brain capacity characterized by a smaller head circumference have a high risk of Alzheimer's disease. However, individuals with a higher cognitive reserve that is operationalized by several years of education have a less risk of Alzheimer's disease (Tucker & Stern, 2011, p.355). Cognitive reserve plays an important role in an individual's risk to develop Alzheimer's disease because it enables a person to compensate for pathology through better use of the available brain reserve. Based on the model of cognitive reserve, people with higher reserve have effectively compensated for pathology in the early stages of this disease.

Cognitive reserve is not fixed since it continues to develop or evolve across the lifespan because of variables associated with lifetime experience. Some of these variables related to lifetime experience that contribute to evolution of cognitive reserve include occupation achievement, education, and leisure activities. These variables play an important role in development of cognitive reserve since they help maintain cognitive function in old age. According to the findings of epidemiological studies, these lifetime experiences can increase reserve and contribute to reduced risk of Alzheimer's disease. A significant portion of patients with Alzheimer's disease progress slowly, which indicates constant need to identify factors that…