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Five Major Mental Disorders Share Genetic Roots, Study Finds
Mental health professionals have known for some time that certain mental disorders tend to appear together with unusual frequency in single individuals. Previously identified examples of paired disorders include bipolar disorder and major depression, bipolar disorder and schizophrenia, and schizophrenia and autism. A new study, published in 2013 in the journal The Lancet, helps explain some of the genetic underpinnings that connect mental illnesses. According to the findings presented in this study, bipolar disorder, major depression, schizophrenia, autism and attention-deficit hyperactivity disorder (ADHD) all stem from one overlapping group of genetic alterations that sometimes appears within human DNA.
DNA and Gene Basics
DNA plays an essential role by providing the basic instructions that the body needs to grow, develop, and function normally. Almost all cells within the body contain the same basic DNA, which is packaged into units called genes. In turn, genes are collected into larger units called chromosomes. In some cases, a single gene within the body controls just one trait or characteristic. However, in many other cases, a single gene helps control multiple characteristics, either by itself or by working together with other genes. The complex interaction between groups of genes helps explain the vast range of variety contained within the human species, since a change in a single gene or gene group can radically alter a person’s appearance, health or behavior.
Genes and Mental Health
In the study published in The Lancet, a multi-university research team examined the DNA of more than 33,000 individuals diagnosed with simultaneous cases of major depression, bipolar disorder, schizophrenia, ADHD, and autism (now known officially as autism spectrum disorders). For comparison’s sake, the team also studied the DNA of almost 28,000 individuals who did not have a diagnosis for any of these conditions. After an extensive analysis, the authors of the study concluded that all five of these mental disorders are linked to alterations in two specific genes responsible for regulating several aspects of human emotion and higher-level mental skills. The authors also concluded that all of the disorders are linked in varying degrees to four other genetic alterations found on two different chromosomes.
In addition to making their basic findings, the authors of the study in The Lancet concluded that, under any given set of circumstances, the genetic abnormalities they identified can produce separate cases of bipolar disorder, major depression, ADHD, autism or schizophrenia, as well as producing any possible combination of these disorders. An individual’s overall chances of developing any single disorder, or combination of disorders, also depend on other factors known to contribute to the risks for mental illness. Apart from genetics, the Mayo Clinic lists mental illness risk factors that include exposure to drugs or alcohol in the womb, exposure to certain viruses in the womb, substance abuse, traumatic brain injury, exposure to high levels of mental stress, a history of childhood neglect or abuse, social isolation, and chronic physical illness.
Prior to the publication of the study in The Lancet, no researcher had demonstrated the potential for a single group of genetic mutations to have such a wide-ranging effect on mental health. The discovery of this common link gives mental health professionals a powerful tool for understanding why their patients sometimes meet the diagnostic requirements for more than one major mental illness. It also helps put other potential causes of a multi-illness diagnosis—such as simple misdiagnosis and poorly designed mental disorder definitions—into perspective, and may help doctors feel more secure when making multiple diagnoses in the future. In addition, it appears that some of the genetic mutations responsible for mental illness also play important roles in the onset of certain serious physical problems, including seizures, high blood pressure and heartbeat irregularities.
The authors of the study in The Lancet note that their work does not conclusively prove that the genetic mutations they identified actually cause bipolar disorder or any of the other disorders in question. Instead, their work merely points out an unusually strong association between certain mutations and certain mental illnesses. Before anyone can say for sure that a given mutation causes a given illness, researchers will need to design and carry out additional large-scale studies designed to answer some very complex scientific questions.