Introduction
Mental health is perhaps one the most important forms of health that humans consider to be vital. Several mental conditions such as Alzheimer’s and depression have been recorded with high prevalence in the society and this has alarmed medical practitioners and government bodies as well . While these condition may abound, little knowledge exist as to the manner in which they occur and treatment methods. Scholars and medical practitioners have taken time and effort in the endeavor to comprehend the causes and treatment methods of mental disorders. However, since the biological processes that lead to mental illnesses are quite intricate and complicated to understand, several hypotheses have been developed to assist studies. Genetics and environmental factors have been associated with numerous mental disorders. Some experts have asserted that the possibility or genetic susceptibility and the presence of the right of environmental factors could lead to some of the mental disorders. This research paper evaluates in the relation between environmental factors, genetics and mental disorders such as depression. The paper will provide a succinct analysis of the term depression. The paper will analyze some aspects regarding genetics and susceptibility to depression. The research will also provide an analysis of the possibility of environmental processes that may increase susceptibility to depression.
Introduction to depression
Depression may be defined as a combination of numerous mental disorders that exhibit different characteristics and reflect several mental alteration in emotional processes, cognitive abilities and psychomotor. Each individual exhibits rather diverse profiles, severity and course on these disorders. Similarly the treatment regiment and response for each of these patients have been differentiated. Genetic epidemiology studies have provided insightful evidence into the fact that mood disorders have variation based on genetic components. Mendel theories of genetics and inheritance provide several assertions regarding health and genetics. Depression has not been found to have direct generational attribute of genetics, however, this paper will attempt to understand the assertion by several scholars about the same.
Genetics, environment and depression
Studies into human epidemiology on depression have uncovered a general risk vulnerability of about 2% to 19% of any one suffering from the said mental disorder (McNeil, Cantor-Graae and Weinberger, 32). However, for persons who are family members of patients, especially those of the first consanguinity, then the prevalence changes to between 5% and 25%. In other analysis of families suffering major depression, statistics indicate similarity in the symptoms that the disease exhibit. Multiple kinds of depression features seem to exist for familial depression cases.
Moreover, there persists additional evidence in twin and family based research on susceptibility to depression. Cooper, agrees that this susceptibility is found to increase three fold in twins and first relatives (41). This is predominantly the case in major depression cases. One such study has directly pointed out evidence of increased susceptibility from genetics. The study was conducted on patients with Alzheimer’s disease (AD) with their genetic components thoroughly examined. In this study, there was evidence pointing to the fact that there exists an allelic association between Alzheimer’s disease and an allele of the apolipoprotein E (APOE) gene (Lesch,32). In this finding, evidence suggest that an individual’s risk of contacting AD increases six fold if the individual is found to have one or two copies of the APOE protein in the gene. The said protein is said to be only a susceptibility gene. Cooper, (51) asserts that it is not a causative or necessary agent for the development of AD.
Nevertheless, understanding a candidate genetic material and the existence of mental disorders is still a matter of debate in past studies. This is due to the fact that there is extremely insufficient information and facts on biological processes that leads to mental disorders. Lesch (84) argues that of all the diseases that affect man, it is mental disorders that is least understood by biologists. Researchers have to find less determinate methods and a myriad of hypotheses in order to develop such an analysis.
Conversely, McNeil, Cantor-Graae, & Weinberger (60), dispute that genetics alone can provide enough evidence for susceptibility. Environmental factors, according to McNeil, et al, have a considerable influence on the manner in which such depression exhibits itself (62). However, determining the extent to which the interaction of such environmental factors and genetics impacts depression remains a great challenge.
This relation between the environmental factors and gene susceptibility and their impacts as expressed in differentiated depression is an observable fact referred to as gene-environment correlation. In appreciating these issues, individual genotype exposure to different environmental factors may provide evidence towards such an assertion. This implies that if a single genotype , with the same components (such as monozygotic twins) was to be exposed to different environmental factors, McNeil, et al, argue that a similar case of depression will exhibit different symptoms.
An additional study sought to establish a gene-environment correlation in the case of AD. In this particular study, there was evidence of an association between the presence of the gene APOE protein content and in a case of a head injury. Lesch (84) stresses that with the existence of the gene and a history of head injury, the risk of AD was found to increase nearly tenfold. Subsequent studies into the impact of head injuries on AD found that head injuries had a significant impact on biological processes. In this case, head injuries influenced the pathogenesis of AD, largely attributed to an increase beta-amyloid precursor protein (APP). The increase in APP is said to exacerbate the occurrence the APOE protein in the body thus increasing susceptibility to AD.
A separate analysis of a case of gene-environment correlation to mental disorders is found in schizophrenia. Malaspina, Goetz and Friedman clarify that head injuries were found to have a significant relation to schizophrenia (54). Schizophrenic pedigrees in comparative studies found that a large portion of the patients had history of head injuries (Cooper, 59). However, studies into the gene vulnerability due to such head injuries were rather open to doubts in the case of schizophrenia. Other mental disorders have different gene-environment correlation. Some quantitative studies into family cases and environmental factors have been undertaken. Such studies looked into twins’ relations, adoption and association. Quantitative research on these matters may provide open ended discussions into the possibility of family and gene factors and its impacts on mental disorders.
Cases of Twin Studies
Twins have been found to a very excellent means in understanding the fundamental concepts of genetic and environment correlation and its impact as found in mental disorders. Studies into Monozygotic (MZ) discordant twins can present elaborate indication into the non-inherited character of mental disorders (Tsuang, Stone and Faraone,32). This is due to the fact that MZ twins have a similar genotype and any variations in character can fully be attributed to environmental factors. Such evaluation can best be done in comparative studies into heritability and genetic variation due to the presence or absence of some environmental risk factors. McNeil, et al, (82) asserts that the magnitude or orders of depression and other mental disorder smay be significantly influenced by a combination of genetic and environmental issues in moderation. Therefore, for such a study to work there must be significant differences in the environments that such discordant twins are exposed for plausible differences and conclusions.
Some studies have been undertaken on large population-based samples of twins to evaluating impacts of life events on major depression (MD) in women (Malaspina, Goetz and Friedman, 47). Related research were performed to look into the gene-environment correlation with regard to Generalized Anxiety Disorder (GAD). Evidence pointed out that common familial environments and genetic factors were not found to have significant impact on how these disorders manifest. Yet, different environment occurrences such as stressful life events, such as loss of a close family member, may have had a significant influence on both GAD and MD. In this respect, Cooper (72) suggest that there is strong possibility that environmental factors play a crucial role on whether females express higher vulnerability to such mental disorders.
Mental disoders from Neurodevelopment Disorder
The growth process of a human body is principally a culmination of interactions between genetic components and the environment. Methodical examination of the impacts of gene-environment interaction and neurological development disorder may provide essential insights into the impact of this interaction o mental disorders. Etiological factors as displayed by environmental and genetic interaction begin at early stages of development and any disorder in the development is exaggerated by genetic vulnerability (Tsuang, et al 64). Thus the severity of cases vary with the degree to which gene-environment interaction varies. According to Lesch (84) these factors depend on the presence or absence of genetic vulnerability and the presence of appropriate environment factors.
Two cases of neurodevelopment disorders commonly associated with gene-environment interaction are autism and schizophrenia. Schizotaxia is term developed to refer to the condition or the state of susceptibility to schizophrenia (Cooper, 91). According to Cooper schizotaxia is based on neurodevelopment of the individual and the condition is set to be determined by the gene-environment interaction. Early exposure, especially in childhood, to adverse environmental conditions such as obstetric complications affects the neurodevelopment of the individual. The results are irregularities expressed in social, cognitive and neurobiological deficits at childhood.
Analysis
The above discussion has clearly identified studies into gene-environment interaction as an open and inconslusive field in psychiatry. Nonetheless, there are essential results that have come out of these studies. First,most studies have established that there is a considerable increase in susceptibility to mental disorder based on genetics. In this sense, reviews into families and twin cases suffering AD and Schizophrenia have ascertained an increase in the susceptibility by about six folds. But a more important finding is that genetics factors only increase the vulnerability but not major etiologic factor.
With th above assertion in mind, the next imperative subject of debate is the impact of environmental factors that would aggravate gene susceptibility. These research studies have established that cases of schizophrenia and AD is said to increase in persons who have suffered major head injury in the past. Evidence has found out that a significant number of cases increased in individuals with a history of head injury.
Twin studies have also presented important argument on matter concerning gene-environment interaction. In studies involving women MZ twins, women who had undergo a stressful life event, such as marriage breakup or death of a close family member, gene susceptible of an individual increased nearly ten folds as compared to the non affected twin. Other studies point to the fact that neurodevelopment disorder based on gene-environment interaction is equally important in future development of mental disorders in adults.
Coclusion
While, none of these studies seem to be quite conclusive in most matters,there is compelling evidence that genetics and enviromental factors have a bearing on mental disorders. Future studies need to utilize advanced technology that we now have. Exact gene mappings and vulnerability to mental disorders is one of the areas that can be clearly identified. For instance, cases of autism have been directed towards purely genetic etiologic factors. In that, several cases of autism have not found any relation to environmental factors. The implication is that in depth analysis into the gene component responsible for autism can be performed to discern these issues.
Works Cited
Cooper, B. "Nature, nurture and mental disorder: old concepts in the new millennium." Br J Psychiatry (2001): 91-101.
Lesch, Klaus Peter. "Gene–environment interaction and the genetics of depression." Journal of Psychiatry and Neurosceince. (2004): 174-184.
Malaspina, D, RR Goetz and JH Friedman. "Traumatic brain injury and schizophrenia in members of schizophrenia and bipolar disorder pedigrees." American Journal of Psychaitry (2001): 440-446.
McNeil, TF, E Cantor-Graae and DR Weinberger. "Relationship of obstetric complications and differences in size of brain structures in monozygotic twins pairs discordant for schizophrenia." American Journal of Psychiatry (2000): 2003-212.
Tsuang, MT, WS Stone and SV. Faraone. "Understanding predisposition to schizophrenia: toward intervention and prevention." Canadian Journal of psychiatry (2002): 518-526.
World Health Organization. Global health risks: mortality and burden of disease attributable to selected major risks. Geneva: World Health Organization, 2009.
