Genetics and Epigenetics of Mental Illness: Implications for Diagnosis and Treatment

Epigenetics encompasses environmental and experiential processes in gene expression that determine when and whether a gene product is produced. However, there is no known gene for any psychiatric disorder, nor is there ever expected to be one. Genes do not code for psychiatric disorders or psychiatric symptoms, they code for proteins and epigenetic regulators that regulate the efficiency of information processing in brain circuitry. These brain circuits can be visualized utilizing various neuroimaging techniques. Every abnormal symptom has an abnormal circuit associated with it, but not every abnormal circuit has an abnormal symptom associated with it. Currently, psychiatric disorders are categorical collections of symptoms chosen by a committee of experts. The Research Domain Criteria (RDoC) created by the National Institute of Mental Health, proposes a dimensional approach for classifying psychiatric symptoms and behaviors related to various brain circuits. This diagnostic strategy is an attempt to link symptom domains that cut across multiple psychiatric disorders first to inefficient information processing in specific brain circuits and eventually to genes regulating those circuits. These advances in understanding the role of genetics may help mental health clinicians improve the understanding of mental illness and subsequent treatment outcomes. Keywords: epigenetics; genetics; research domain criteria; brain mapping; biomarkers; psychiatry; psychiatric; neurodevelopment; brain imaging; psychotherapy