Genes linked to schizophrenia identified in ancestral African population
by Tianna Hicklin, Ph.D./National Institutes of Health
At a Glance
- Researchers found damaging genetic variants linked to schizophrenia in the Xhosa population of South Africa.
- The findings suggest that though the mutations involved in the disorder are different for each individual, genes with the same functions are involved in all populations.
Schizophrenia is a chronic and severe mental disorder. It affects how a person thinks, feels, and behaves. People with schizophrenia can experience hallucinations, delusions, and disordered thinking. Symptoms can be very disabling.
No single gene causes this disorder. Rather, many different genes are involved, with each patient carrying one or more severe mutations. Most genetic studies of schizophrenia to date have been carried out in people of European and Asian descent. However, African populations harbor the most genetic diversity because most of human evolution occurred in Africa. A relatively small number of people emigrated 50,000 to 100,000 years ago to establish other populations.
To identify and characterize genes related to schizophrenia in an ancestral African population, an international team of researchers sequenced and compared the genomes of more than 1,800 people who identified themselves as Xhosa. Xhosa people live throughout South Africa and are the largest population of the Eastern Cape region. About half the participants had been diagnosed with schizophrenia and half were not.
The research team was led by Drs. Mary-Claire King and Jon M. McClellan at the University of Washington, Dan Stein at the University of Cape Town, South Africa, and Ezra Susser at Columbia University. Their work was funded in part by NIH’s National Institute of Mental Health (NIMH) and National Human Genome Research Institute (NHGRI). Results were published online on January 31, 2020, in Science.
The researchers found that genetic variation, in general, was greater in the Xhosa population compared with the largely non-African genomes that have been studied in the past.
The team then looked for changes in sequence, or mutations, in the exome—the set of genes that code for proteins. They found that people with schizophrenia were more likely to have unique, damaging mutations in their genes.
Those with the disorder were also more likely to have these mutations specifically in genes involved in brain development and in the functioning of synapses, which carry out communication between brain cells.
The team compared these genetic changes in the Xhosa population with those from genetic studies of people with schizophrenia from Sweden. Both studies found mutations in genes related to synaptic function. However, the results from the Xhosa study showed larger effect sizes. The authors suggest that the greater genetic diversity in the African population increases the power of genetic studies to identify genes related to behavioral disorders.
“The presence of only a few DNA variations damaging to synaptic function could have an outsized effect on schizophrenia,” Susser says. “While these variants differ from person to person, we believe they may disrupt neural pathways that elevate the risk for schizophrenia.”
“The genes and pathways identified by this research inform the understanding of schizophrenia for all human populations,” King adds, “and suggest potential mechanisms for the design of more effective treatments.”