Two large, international studies have independently found three genetic mutations that are linked to a greatly increased risk of schizophrenia, but say the rare mutations only account for a small percentage of schizophrenia cases. The identification of the three mutations is being hailed as a breakthrough, as no genetic factors had been definitively linked to the disease before. But in a finding of even greater importance, the studies suggest that there’s no easy answer to the question of what causes the devastating mental illness. Instead of a common genetic problem, schizophrenia may be triggered by many rare mutations that cause subtly different variants of the disease.
“What is beginning to emerge is that a lot of the risk of brain diseases is conferred by rare [genetic] deletions,” [study author Kari] Stefansson said…. The new focus on rare mutations suggests that natural selection is highly efficient at removing schizophrenia-causing genes from the population. Despite selection against the disease, according to this new idea, schizophrenia continues to appear because it is driven by a spate of new mutations that occur all the time in the population. [The New York Times].
Researchers have made a map of the human brain that shows a dense network of connections at the top of the 
