Certain genes called retrotransposons — also known as jumping genes — are more common in the brains of people with schizophrenia, according to new research published in the journal Neuron.
Jumping genes are mobile elements that copy and paste themselves at various places throughout the genome. They make up about half of the human genome, compared with the 1 percent of genes that actually code for making proteins, said study co-author Dr. Tadafumi Kato, a neurobiologist at the RIKEN Brain Science Institute in Japan.
The research suggest these jumping genes may alter how neurons (nerve cells in the brain) form during development, and in turn increase the risk for developing schizophrenia, said Kato.
Prior research has found that a certain type of jumping gene, known as long interspersed nuclear element-1 (LINE-1), was active in human brain cells. The researchers wondered whether these genes played a role in mental illness. To find out, they conducted a post-mortem analysis of 120 human brains, 13 belonging to people who had been diagnosed with schizophrenia.
The findings revealed a greater number of LINE-1 copies in the brains of schizophrenics compared with other groups.
Furthermore, stem cells that came from the brains of people with schizophrenia had a higher concentration of LINE-1 genes than those from people without the disorder. (Stem cells are body cells that haven’t yet become specialized into, for example, skin or liver cells, and have the capability to develop into any tissue in the body.)
The team also found that in people with schizophrenia, greater concentrations of LINE-1 genes were found near genes associated with mental disorders associated with how neurons in the brain communicate with one another.
Perhaps these LINE-1 segments are inserting themselves into genes critical for brain development. When triggered by genetic and or environmental factors, they may alter that brain development, leading to schizophrenia, Kato said.
The findings are “very convincing,” because the team used so many different methods to tie the jumping genes to schizophrenia, said Alysson Muotri, a neurobiologist at the University of California at San Diego. And LINE-1 genes may actually serve some beneficial purpose for people, he added.
“LINE-1 retrotransposition may be a mechanism to generate cognitive diversity in the human population,” Muotri said. “This mechanism may have evolved to create outliers in the population, people with extraordinary abilities. On the other hand, the other end of the spectrum may be patients with schizophrenia or autism.”