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Psychiatric genetics, a subfield of behavioral neurogenetics, studies the role of genetics in psychological conditions such as alcoholism, schizophrenia, bipolar disorder, and autism. The basic principle behind psychiatric genetics is that genetic polymorphisms, as indicated by linkage to e.g. a single nucleotide polymorphism (SNP), are part of the etiology of psychiatric disorders.
Psychiatric genetics is a somewhat new name for an old question, "Are behavioral and psychological conditions and deviations inherited". The goal of psychiatric genetics is to better understand the etiology of psychiatric disorders, to use that knowledge to improve treatment methods, and possibly also to develop personalized treatments based on genetic profiles (see pharmacogenomics). In other words, the goal is to transform parts of psychiatry into a neuroscience-based discipline.
Research on psychiatric genetics began in the late nineteenth century with Francis Galton (a founder of psychiatric genetics) who was motivated by the work of Charles Darwin and his concept of desegregation. These methods of study later improved due to the development of more advanced clinical, epidemiological, and biometrical research tools. Better research tools were the precursor to the ability to perform valid family, twin, and adoption studies. Researchers learned that genes influence how these disorders manifest and that they tend to aggregate in families.
Most psychiatric disorders are highly heritable; the estimated heritability for bipolar disorder, schizophrenia, and autism (80% or higher) is much higher than that of diseases like breast cancer and Parkinson disease. Having a close family member affected by a mental illness is the largest known risk factor, to date. However, linkage analysis and genome-wide association studies have found few reproducible risk factors.
Heterogeneity is an important factor to consider when dealing with genetics. Two types of heterogeneity have been identified in association with psychiatric genetics: causal and clinical. Causal heterogeneity refers to a situation in which two or more causes can independently induce the same clinical syndrome. Clinical heterogeneity refers to when a single cause can lead to more than one clinical syndrome.
Several genetic risk factors have been found with the endophenotypes of psychiatric disorders, rather than with the diagnoses themselves. That is, the risk factors are associated with particular symptoms, not with the overall diagnosis. In psychiatry, endophenotypes are a way of objectively measuring certain internal processes in a reliable way that is often lacking the diseases with which they are associated. They lie in the space between genes and disease process and allow for some understanding of the biology of psychiatric diseases.
Genetic Linkage studies attempt to find a correlation between the diagnosis and inheritance of certain alleles within families who have two or more ill relatives. An analysis of a linkage study uses a wide chromosomal region, whereas a genetic association study endeavors to identify a specific DNA polymorphism, which can be a deletion, inversion, or repletion of a sequence. Case-control association studies can be used as an exploratory tool for narrowing the area of interest after preliminary mapping of a gene by a linkage study.
There are many way in which genetics are becoming more and more important every day. One hope for future genetic testing is the ability to test for presymptomatic or prenatal illnesses. This information has the potential to improve the lives of those affected with certain illnesses, specifically those like schizophrenia. If possible to test for schizophrenia before the symptoms develop, proactive interventions could be developed, or even preventative treatments. In one study, 100% of patients with bipolar disorder indicated that they would probably take a genetic test to determine if he or she were carrying a gene associated with the disorder, if such a test existed.
Francis Galton studied both desirable and undesirable behavioral and mental properties to better examine the world of genetics. His research led to his proposal of a eugenic program of birth control. His goal was to decrease the frequency of the less desirable traits that occurred throughout the population. Galton later reevaluated and changed his conclusion due to the possibility of polygenic transmission, but his ideas were still pursued by other psychiatrists, specifically some in German and Scandinavia.
Genotyping and its implications are still seen as ethically controversial by many people. The findings can undermine what constitutes someones "self." In response to past consequences of psychiatric genetics, the ELSI, or the Ethical, Legal, and Social Initiative (National Institute of Health's Genome Project) was created. Hopefully the ELSI will address any genetics related ethical issues and will allow research in this area to continue, while avoiding harmful consequences.