Scientists reported that they have taken a significant step towards understanding the cause of schizophrenia, in a landmark study that provides the first rigorously tested insight into the biology behind any common psychiatric disorder. More than two million Americans suffer from schizophrenia, which is characterised by delusional thinking and hallucinations. The drugs available to treat it blunt some of its symptoms but do not touch the underlying cause. The finding will not lead to new treatments soon, but the results provide researchers with their first biological handle on an ancient disorder whose cause has confounded modern science for generations. The finding also helps explain some other mysteries, including why the disorder often begins in adolescence or young adulthood. The researchers pieced together the steps by which genes can increase a person's risk of developing schizophrenia. That risk, they found, is tied to a natural process called synaptic pruning, in which the brain sheds weak or redundant connections between neurons as it matures. During adolescence and early adulthood, this activity takes place primarily in the section of the brain where thinking and planning skills are centered, known as the prefrontal cortex.
People who carry genes that accelerate or intensify that pruning are at higher risk of developing schizophrenia than those who do not, the new study suggests. Some researchers had suspected that the pruning must somehow go awry in people with schizophrenia, because previous studies showed that their prefrontal areas tended to have a diminished number of neural connections. The new paper not only strongly supports that this is the case, but also explains it and identifies the genes responsible: People with schizophrenia have a gene variant that apparently facilitates aggressive 'tagging' of connections for pruning, in effect accelerating the process.
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