A New Study Explores Why Multiple Diagnoses Are Common With Mental Illness

Much research has been invested in identifying susceptibility genes for schizophrenia and bipolar disorder. Several well-established linkages have emerged in schizophrenia.

“Relatives of people with schizophrenia have a greater risk of developing the illness, the risk being progressively higher among those who are more genetically similar to the person with schizophrenia,” wrote Colorado Recovery founder Richard Warner in his book The Environment of Schizophrenia.

“Evidence accumulated during the 20th century for a substantial genetic contribution to the etiology of both schizophrenia and bipolar disorder, with the genetic influences initially appearing to be largely distinct for each disorder. This reinforced the traditional concept of the Kraepelinian dichotomy, in which the two disorders were viewed as etiologically independent. The picture has now significantly changed to one of partial overlap in genetic influences, although many of the details about what is shared and independent remain to be elucidated. The dichotomy concept has thus been severely weakened but persists in diagnostic classification systems,” wrote Alastair Cardno and Michael Owen in their 2014 study on the genetic relationships between schizophrenia, bipolar disorder, and schizoaffective disorder.

Not only is there an overlap in genetic influences in schizophrenia and bipolar disorder, but more than half of patients diagnosed with one psychiatric disorder will also be diagnosed with a second or third mental illness in their lifetime. About a third have four or more.

A comprehensive new analysis of eleven major psychiatric disorders offers new insight into why comorbidities are the norm, rather than the exception. The study, published in the journal Nature Genetics, found that while there is no particular gene or set of genes driving an underlying risk for all of them, subsets of disorders—including bipolar disorder and schizophrenia; anorexia nervosa and obsessive-compulsive disorder; and major depression and anxiety—do share a common genetic architecture.

“Our findings confirm that high comorbidity across some disorders in part reflects overlapping pathways of genetic risk,” said lead author Andrew Grotzinger, an assistant professor in the Department of Psychology and Neuroscience at the University of Colorado at Boulder.

For the study, Grotzinger and colleagues at the University of Texas at Austin, Vrije Universiteit Amsterdam, and other collaborating institutions analyzed publicly available genome-wide association (GWAS) data from hundreds of thousands of people who submitted genetic material to large-scale datasets, such as the UK Biobank and the Psychiatric Genomics Consortium.

They found that 70 percent of the genetic signal associated with schizophrenia is also associated with bipolar disorder. That finding was surprising as, under current diagnostic guidelines, clinicians typically will not diagnose an individual with both.

The researchers also found that anorexia nervosa and obsessive-compulsive disorder have a strong, shared genetic architecture and that people with a genetic predisposition to have a smaller body type or low body mass index also tend to have a genetic predisposition to these disorders.

The eleven disorders included in the study were schizophrenia, bipolar disorder, major depressive disorder, anxiety disorder, anorexia nervosa, obsessive-compulsive disorder, Tourette syndrome, post-traumatic stress disorder, alcohol misuse, ADHD, and autism.

While more research is necessary to find out what the identified genes do, Grotzinger sees the results of his study as a first step toward developing therapies to address multiple disorders with one treatment.

“People are more likely today to be prescribed multiple medications intended to treat multiple diagnoses and in some instances, those medicines can have side effects,” he said. “By identifying what is shared across these issues, we can hopefully come up with ways to target them in a different way that doesn’t require four separate pills or four separate psychotherapy interventions.”

Colorado Recovery provides services for adults with serious mental illnesses that will stabilize their illness, minimize symptoms, improve functioning and enhance each person’s social inclusion, quality of life, and sense of meaning in life. We provide residential and outpatient treatment options for schizophrenia, bipolar, schizoaffective disorder, and other mental health conditions. Call us at 720-218-4068 to discuss treatment options for you or the person you would like to help.