The Etiology of Schizophrenia - Coursework Example

The Aetiology of Schizophrenia Introduction: Schizophrenia is a complex disease that has remained a puzzle to the medical and scientific community. It remains a puzzle as it has not been possible for scientific investigators to identify a single factor that can be used to characterize schizophrenia as seen in all patients in spite of decades of disease. Schizophrenia manifests during adolescence or early adulthood through the presentation of psychotic symptoms, which include auditory hallucinations and delusions, social withdrawal, flattened effect, poor motivation, and depressed mood (Rasmussen, 2006). Efforts to unravel the mystery that shrouds an understanding of the aetiology of schizophrenia that can lead to better intervention means continues, for schizophrenia is among the major public health problems that societies around the world have to confront. Schizophrenia is a common occurrence with nearly one percent of the world population likely to be affected by it. The consequences of schizophrenia are severe. Most of the affected individuals are unable to return to the work place or to classrooms, as part of their normal family or social responsibilities and require support for the rest of their lives. The disruption of their normal life causes leads to a high rate of suicides of up to ten percent in those individuals affected by schizophrenia. The economic costs to society as a result of schizophrenia run into billions of pounds (Andreasan, 2000). Aetiology of Schizophrenia: Though the aetiology of schizophrenia is not clearly understood it is becoming clear that it is a heterogeneous disease with a number of possible causes impacting on the possible development of schizophrenia, which has led to these being classified under different nomenclatures. The aetiology of schizophrenia is better understood by examining the classifications of the causative factors of schizophrenia, which come under two heads of genetic vulnerability and environmental vulnerability. Findings that emerged from data taken from twin and adoption studies of schizophrenia have clearly linked genetic factors and environmental factors to the development of schizophrenia. A large amount of research has gone into understanding the aetiology of schizophrenia, which has resulted in a clearer picture emerging of some of the individual factors that contribute to the development of schizophrenia than was known earlier. However, in spite of these fascinating new insights into the aetiology of schizophrenia, it must be remembered that there remains much to be understood regarding the aetiology of schizophrenia (Austin, 2005). Genetic Vulnerability in the Aetiology of Schizophrenia: While it has not been difficult to identify the heritability of schizophrenia, which is estimated to be between sixty to eighty-five percent, it has proved to be extremely difficult to identify the genes that are responsible for the genetic vulnerability to schizophrenia. There are several factors that contribute to this. According to Austin, 2005, a partial contributor to this haze around the genetic vulnerability of schizophrenia is the very nature of the genetic contributions. The model that is best suited to explain the observed patterns in the inheritance of schizophrenia calls for the interaction of at least three genes and the environment. The more the number of genes involved in a particular disease the more the difficulty in identifying them and this is the case with in the attempt the genes involved in the genetic vulnerability to schizophrenia (Austin, 2005). The search for the candidate genes involved in schizophrenia has thrown up a number of possibilities, the definiteness of which is impeded by the research method needed to ensure the validity of the findings. Since each of the three individual genes makes a small contribution to the development of schizophrenia, a very large sample size is needed to create the required dimensions to identify the relatively small impact of each individual gene. Such large sample sizes are difficult to come by (Austin, 2005). Yet another issue that has impeded identifying the genes involved in the development of schizophrenia is the belief that in the case of a majority of the individuals a small number of genes interacting with the environment are responsible for the development of the illness, but in a small number of individuals it is a pool of many genes that increase the vulnerability to the illness and in different individuals this gene pool may operate in different combinations. In addition is the possibility that has emerged from evidence that in very few cases families demonstrate schizophrenia form a single gene that has a major effect (Austin, 2005). The difficulties in identifying the genes that might have a role to play in the development of schizophrenia do not end there. Yet another issue is replication. Confidence levels of findings of candidate genes from a single report are low and it needs replication of the findings through further research for confidence levels to be enhanced for acceptance. Many years of research have yielded several possible genes, but none of these findings have been replicated for acceptance with confidence that they do indeed have a role to play in the development of schizophrenia (Austin, 2005). The lack of success in applying the traditional genetic models to the aetiology of schizophrenia has resulted in newer concepts of genetic models for aetiology of schizophrenia. One such concept is that there is no gene of major effect. Instead multiple genetic loci of modest effect that are interactive in combination are responsible for the true cumulative of the disease. This is in sharp contrast to diseases alleles involved in single gene disorders like Huntington’s disease. In such diseases of disease alleles increase the potential risk of the disease five thousand times. This suggested genetic model for the aetiology of schizophrenia implies that the disease alleles associated with schizophrenia have a considerably lower potential risk for the disease individually, which may be as low as two or three times (Pearlson, 2000). Another new concept aimed at the understanding of the aetiology of schizophrenia is genetic predisposition of the disease interacting with one or more of the several environmental factors during the development stages of the brain to cause the illness. This is similar to the concept in Alzheimer’s disease, where disparate susceptibility genes converge through multiple genetic paths in a given sample population to converge on a common phenotype (Pearlson, 2000). The new concepts appear to be unnecessarily complicated, but in the given state of the lack of clarity in the aetiology offer newer means to its understanding. Such concepts to understanding of the aetiology of diseases are not a novel idea, nor are they considered only in the disease of schizophrenia. Such intricate inheritance models are being hypothesized for other complex inheritance diseases like hypertension, type 2 diabetes and obesity (Pearlson, 2000). The genetic linkage to schizophrenia is well established from evidence of several studies. Yet it is insufficient to explain the aetiology of schizophrenia in full and it this becomes even clearer when the heritability of schizophrenia is estimated to lie between sixty and eighty-five percent. This means that there are other factors to be considered in the aetiology of schizophrenia. It is seen from evidence that has emerged from studies that genetic influences very frequently act in combination with environmental factors in the aetiology of schizophrenia. This gives rise to the current diathesis-stress models of aetiology of schizophrenia. The diathesis-stress models in the aetiology of schizophrenia suggest that inherited factors are genetically determined characteristics of the brain that impact upon the structure and function of the brain. Vulnerabilities can also be acquired from prenatal events and post natal stressors that gave an impact on the structure on the brain. Though the vulnerability to schizophrenia in most cases is congenital, vulnerability is enhanced through the environmental stressors. Mere presence of congenital vulnerability to schizophrenia is in sufficient for the clinical manifestation of the illness. For this to happen there needs to be one or more environmental stressors acting in concert for the manifestation of the illness (Walker, Kestler, Bollini & Hochman, 2004). Environmental Factors in the Aetiology of Schizophrenia: The environmental factors in the aetiology of schizophrenia are several and are classified under several heads. A significant issue in the environmental factors is that it is difficult to prioritize or assign greater vulnerability for schizophrenia, though there is some evidence of some of these factors having greater risk significance than the others. One feature however stands out and that is the relative risk associated with the genetic factors is higher than that of the environment factors, but prevalence of exposure to many of the environmental factors is high and it is this that makes the risk that can be attributed to the environmental factors considerable (Austin, 2005). Obstetric Complications: There are three categories of obstetric complications that increase the vulnerability to schizophrenia. The first is complications of pregnancy which includes preeclampsia, diabetes, Rhesus factor incompatibility and bleeding. The second category arises from complications during delivery and includes atonic uterus, asphyxia and emergency caesarean section. The final category is abnormal foetus development, which is normally associated with low birth weight, though the association between low birth weight and schizophrenia eludes explanation (Austin, 2005). Maternal Nutrition: Evidence from studies suggests that there is the possibility of food deprivation during pregnancy increasing the vulnerability to schizophrenia (Lobato, et al, 2001). Season of Birth: Evidence from epidemiological studies have shown that there is an increased prevalence of births of schizophrenics during the periods of late winter and early spring and the risk for schizophrenia has been linked to the seasonal atmosphere changes that occur during these periods (Ledgerwood, Ewald, & Cochran, 2003). Infection: The issue of viral infection during the pregnancy as a risk factor for schizophrenia has been controversial. Evidence from studies show sufficient evidence to accept that maternal infection with influenza during pregnancy is a risk factor for schizophrenia, while evidence in the case of other viruses remains less convincing (Lobato, et al, 2001). Stress: Stress is a widely accepted risk factor for schizophrenia, though the exact definition of the various factors involved in stress needs to be worked out more clearly (Austin, 2005). Immigration: Observations of the prevalence of schizophrenia among the first generation and second generation immigrants demonstrate an increased risk for schizophrenia, which cannot be explained by any other considerations (Austin, 2005). Use of Drugs: The association between the misuse of drugs and with psychosis and schizophrenia has been established for a long time now. The main drug linked to increased risk for schizophrenia is cannabis (Austin, 2005). Family Influence: Stress has been seen as a factor that increases the risk for schizophrenia. When there is increased stress due to inflexible and inadaptable approaches in the family, the stress increases and so does the risk for schizophrenia, if there is already a genetic disposition for it. Such inflexibility and lack of willingness to adapt to change environments within the family may come from cultural influences and this implies that strong inflexible cultures may have a bearing on the increased risk for schizophrenia (Wuerker, 2000). The familial environmental factors normally taken into consideration, when evaluating the aetiology of schizophrenia are normally psychological issues related to the quality of parenting in general and mothering in particular. Familial biological factors also need to be taken into consideration while evaluating the aetiology of schizophrenia. The familial biological factor that stands out is the transmission of infection, from family and pets. Though the evidence for a role in infection in the risk for schizophrenia, except in the case of influenza during pregnancy, it still remains a potential risk factor. Infections particularly virus are easily transmitted from one member of the family to another. Such infections result from exposure of any family member to these infections as a part of their daily activity. Animal and bird pets can be a reservoir for infectious agents and transmit them to family members (Torrey & Yolken, 2000). Conclusion: The exact aetiology of schizophrenia still remains a mystery. There is strong evidence to suggest that main aetiology of schizophrenia is in genetic factors. From then on the understanding of the aetiology of schizophrenia becomes less clear, because of the complex nature of the nature. Though there is ample evidence for the genetic link with schizophrenia identifying the genes involved has been elusive. This has led to a plethora of possible candidate genes being identified, but the confidence that any or all of these candidate genes are involved in the aetiology of schizophrenia is still low. The lack of clarity in the aetiology of schizophrenia has given rise to many hypotheses on the aetiology of schizophrenia. The most promising of these models for the aetiology of schizophrenia is the model of the hereditary factor being the predisposing factor in the development of schizophrenia, with environmental stressors acting in concert for the manifestation of schizophrenia. Literary Resources Andreasan, C. N. (2000). Schizophrenia: the fundamental questions. Brain Research Reviews, 31, 106-112. Austin, J. (2005). Schizophrenia: An Update and Review. Journal of Genetic Counselling, 14(5), 329-340. Ledgerwood, G. L. Ewald, P. W. & Cochran, G. M. (2003). GENES, GERMS, AND SCHIZOPHRENIA: an evolutionary perspective. Biology and Medicine, 46(3), 317-348. Lobato, M. I. Belmonte-de-Abreu, P. Knijnik, D. Teruchkin, B., Ghisolfi, E. & Henriques, A. (2001). Neurodevelopmental risk factors in schizophrenia. Brazilian Journal of Medical and Biological Research, 34(2), 155-163. Pearlson, D. G. (2000). Neurobiology of Schizophrenia: Annals of Neurology, 48(4), 556-566. Rasmussen, F. (2006). Paternal age, size at birth, and size in young adulthood – risk factors for schizophrenia. European Journal of Endocrinology, 155 (Suppl.1), 65-69. Torrey, F. E. & Yolken, H. R. (2000). Familial and genetic mechanisms in schizophrenia. Brain Research Reviews, 31, 113-117. Walker, E. Kestler, L. Bollini, A & Hochman, M. K. (2004). Schizophrenia: Etiology and Course. Annual Review of Psychology, 55, 401-430. Wuerker, K. A. (2000). THE FAMILY AND SCHIZOPHRENIA. Issues in Mental Health Nursing, 21(1), 127-141. Read More