DNA Tie for Two Disorders: Genetic defects link psychiatric ailments
Schizophrenia and bipolar disorder may share more than a propensity for wreaking havoc on mental life. These severe psychiatric disorders, each of which occurs in about 1 in 100 adults, rest on identical flaws in a set of genes that produce a protective covering for brain cells, a new study suggests.
The critical genes are active in brain cells called oligodendrocytes, say neuroscientist Sabine Bahn of the University of Cambridge in England and her colleagues.
Oligodendrocytes produce fatty myelin molecules that coat brain cells and influence their transmission of electrical impulses.
More than a dozen proteins that oligodendrocytes use to make myelin occurred in unusually low concentrations in the preserved brains of 15 people with schizophrenia and 15 people with bipolar disorder, Bahn’s team reports in the Sept. 6 Lancet. Several other proteins, which regulate the genes that code for the myelin-making proteins, also exhibited low concentrations in both groups of brains. No such disturbances appeared in the preserved brains of 15 people who had had no mental disorder.
“Our findings raise questions about myelin’s role in these psychiatric illnesses,” Bahn says. She’s now directing an analysis of myelin-related proteins in 150 preserved brains from people with schizophrenia, bipolar illness, or no mental disorder.
If the results hold, they will indicate that disrupted myelin production may set the stage for psychosis, a warping of one’s sense of reality that often occurs in schizophrenia, bipolar disorder, and brain ailments such as Alzheimer’s disease, Bahn suggests.
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Signs of schizophrenia include apathy, disorganized behavior, and psychotic symptoms such as hallucinations and delusions. Bipolar disorder, sometimes called manic depression, features swings from severe depression to a type of agitated euphoria called mania. Psychotic delusions, say of being invincible, are a common element of mania.
Earlier studies linked schizophrenia to disturbances in myelin-producing genes in specific brain regions. Further work needs to examine whether the same regional effects characterize bipolar disorder, say Kenneth L. Davis and Vahram Haroutunian, both psychiatrists at Mt. Sinai School of Medicine in New York, in a commentary published with the new report.
Psychiatrist Elliot S. Gershon of the University of Chicago calls Bahn’s report “very interesting and exciting news.” In the May American Journal of Human Genetics, Gershon and his coworkers reported that alterations of two other genes, found on chromosome 13, frequently occur in people with either schizophrenia or bipolar disorder. The functions of those genes are poorly understood.
Accumulating data also suggest that additional genes, located on chromosome 8, contribute both to bipolar disorder and schizophrenia (SN: 9/5/98, p. 151), Gershon adds.
However, any potential link between these two mental disorders is controversial. For instance, a study led by Pekka Tienari of Finland’s University of Oulu found that having a biological mother with schizophrenia didn’t increase rates of bipolar illness and other mood disorders in nearly 400 adults who had been adopted as infants. These results, published in the September American Journal of Psychiatry, clash with the notion that schizophrenia and bipolar disorder share genetic influences.
The two disorders stem from various influences, some shared and some unique, Bahn contends. “It’s like inflammation,” she says. “There can be many causes for the same symptoms.”
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