Psychiatric Disorders

It is well accepted that many of the psychiatric disorders listed in the Diagnostic and Statistical Manual, fourth edition, have hereditary predispositions. (The DSM-IV is the official diagnostic manual for mental disorders in the United States.) In the last two decades, clinical genetic (family, twin, and adoption) studies have provided some valuable information about both the genetic and environmental aspects that lead to the development of these psychiatric disorders. More recently, a growing number of molecular genetics studies have provided more data about the genetics of the disorders. However, there has been little success in the identification of specific genes involved in the etiology of these complex disorders.

The DSM-IV includes more than 350 diagnoses and at least one third of the disorders have had one or more clinical genetic study completed. Additionally, some of the disorders have been subjected to molecular genetic studies. Several of the most frequently examined DSM-IV psychiatric disorders from a "genetic study" perspective are listed below:

• Alcoholism
• Alzheimers
• Attention Deficit Hyperactivity Disorder (ADHD)
• Autism
• Bipolar Disorder
• Mental Retardation
• Obsessive-Compulsive Disorder (OCD)
• Panic Disorder
• Schizophrenia
• Social Phobia
• Substance Use Disorder
• Tourette's Syndrome

Major psychiatric disorders, such as schizophrenia and bipolar disorder, have been shown in numerous studies to have significant genetic factors involved in their etiology. The effects of environment and gene-environment interactions on the expression of the disorders are thought to be important, but need more study. Several childhood onset disorders, such as mental retardation, autism, and ADHD, also have strong genetic components in their etiology. All of these disorders are considered complex and are thought to have multiple genes acting together with nongenetic factors, with each gene typically contributing only small effects.