Psychiatric genetics

Psychiatric genetics is a subfield of behavioral neurogenetics and behavioral genetics which studies the role of genetics in the development of mental disorders (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) are part of the causation of psychiatric disorders. Psychiatric genetics is a subfield of behavioral neurogenetics and behavioral genetics which studies the role of genetics in the development of mental disorders (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) are part of the causation of psychiatric disorders. Psychiatric genetics is a somewhat new name for the old question, 'Are behavioral and psychological conditions and deviations inherited?'. The goal of psychiatric genetics is to better understand the causes 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. Recent advances in molecular biology allowed for the identification of hundreds of common and rare genetic variations that contribute to psychiatric disorders. 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. A systematic comparative analysis of shared and unique genetic factors highlighted key gene sets and molecular processes underlying six major neuropsychiatric disorders: attention deficit hyperactivity disorder, anxiety disorders, autistic spectrum disorders, bipolar disorder, major depressive disorder, and schizophrenia. This may ultimately translate into improved diagnosis and treatment of these debilitating disorders. Linkage, association, and microarray studies generate raw material for findings in psychiatric genetics. Copy number variants have also been associated with psychiatric conditions.