Tiny molecules of microRNAs that control hundreds of genes associated with schizophrenia are underexpressed during fetal development, according to the new study by an international team of researchers. One specific group of these cellular RNA fragments, known as miR-9, were highly underexpressed, making those fetuses particularly vulnerable to developing schizophrenia later in life.
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The genes under miR-9’s control are important to the growth and maturation of neurons in the human fetal brain. Their underexpression, the researchers say, means that certain brain circuits will probably not be wired correctly during prenatal development. The team that conducted the research was based at the Icahn School of Medicine at Mount Sinai in New York; it included biologists, neuroscientists, psychiatrists and mathematicians. It also involved a complex laboratory procedure only five years old.
Most molecular experiments in schizophrenia research are greatly limited because they must be conducted postmortem, on brain tissue derived from deceased patients. The scientists involved in the new study overcame this problem by engineering fetal schizophrenia neurons.
First, they obtained skin samples from living schizophrenia patients, then they reprogrammed the skin cells into embryonic-like stem cells before finally coaxing them to develop into human brain cells. These reverse-engineered schizophrenia neurons, akin to fetal cells in the first or second trimester of a woman’s pregnancy, became the basis for the study.
The importance of the discovery was underscored by the fact that these “perturbed” miR-9 levels, which appear responsible for deficiencies in fetal brain development, have not been detected in the brains of schizophrenia patients after death.
“If the impact of these genetic variations is indeed during early cortical development,” the authors of the study wrote, “this would be consistent with our inability to detect perturbed miR-9 levels in post-mortem [brain tissue].”
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The sample size of the Mount Sinai study was admittedly small — just four schizophrenia patients — but in a second, slightly larger study of 14 patients, conducted by the National Institutes of Health, the results were replicated.
“These findings support a model of an extremely complex genetic architecture underlying schizophrenia risk,” the report said, “one in which miR-9 is just one of many factors contributing to schizophrenia predisposition in a subset of patients.”
More than 1,000 genes have been associated with schizophrenia in recent years, but the social significance of these most recent findings, Brennand said, cannot be overstated.
“What I hope it tells parents is that it’s not their fault,” Brennand said. “If science can do anything, even before new treatments, maybe we can at least change attitudes.”