Law Assignment代写 单一原因
There is no single known cause or a single factor sufficient by itself to lead to AD; multiple factors are thought to function in sequence or combination to cause the disease. AD is a complex process, involving many factors that affect the brain over a long time. Currently, Hendrie (2001) documents that so far two risk factors are linked to the disease while several others are under investigation. Known risk factors are age and family history/genetic disposition. The risk of AD increases exponentially with age, doubling in each decade after 65 (Wilson and Bennett, 2003). Individuals from families with a history of AD have a more risk of developing the disease. To date, researchers have pointed out the three genes responsible for the genetic link of the disease (Bekris, Yu, Bird and Tsuang, 2010). Other potential risk factors include gender and educational level. Females are more susceptible to the disease, but their incidences could be because of the effects of age - on average female gender is known to live longer than male gender (Hendrie, 2001). In relation to educational level, a research by Wilson and Bennett (2003) alludes, individuals who have more years of formal education have a lower risk of developing AD in old age compared to individuals with lower educational levels.
Environmental aspects and metabolism disorders have also been linked to development of AD. The most studied environmental suspects are metal poisoning with zinc and aluminum, viral infections and foodborne poisons. Aluminum became a suspect in AD after autopsy studies demonstrated trace amounts of the metal in individuals who had succumbed to AD (Hendrie, 2001). Although many studies since have not been able to confirm this finding beyond doubt or have had questionable results, it is evident that aluminum occurs in higher concentrations than usual in several autopsy findings of Alzheimer's patients. Wilson and Bennett (2003) suggest a higher risk of AD among individuals used antiperspirants and antacids with high concentrations of aluminum. Zinc has been implicated in AD in two ways. Some researchers hypothesize low zinc levels could be responsible while others argue that high zinc levels could be the problem (Hendrie, 2001). Low zinc levels were implied by postmortem studies that found low levels of zinc in the brains (especially the hippocampus) of patients who had succumbed to AD. In contrast, another research alludes that excess zinc levels may be responsible (Hendrie, 2001). In this research, zinc was demonstrated to precipitate soluble beta amyloids in the cerebrospinal fluid into clumps like the plaques demonstrated in the brains of AD patients (Hendrie, 2001). Foodborne poisons such as toxins have been associated with some types of dementia. Some legume seeds have been confirmed contain amino acids that may cause neurological damage when ingested. Both act by enhancing the activity of the neurotransmitter glutamate, also implicated in AD. In Canada, an epidemic of a neurological disease analogous to AD occurred among people who had eaten muscles contaminated with Demoic acid, a glutamate stimulator (Wilson and Bennett, 2003). Viruses have been suggested in AD because, in the past, viruses have been demonstrated to lead to some neurological diseases years after entering the body. So for years, Goedert and Spillantini (2006) document that researchers have sought viruses or other infectious agents in AD.