A new study suggests that schizophrenia debilitating disease can be a byproduct of genetic changes that have fueled the evolution of the expansive human brain. The idea, still preliminary, is that the massive energy demands of the brain can make it vulnerable to mutations in genes related to metabolism.
Up to 1% of people will eventually be diagnosed with schizophrenia, a disease that can cause delusions and hallucinations and severely impair the ability of a person to communicate with others. No one knows what causes schizophrenia, although recent research involves defective genes. Because schizophrenia affects "social cognition", a characteristic of human evolution, some researchers have speculated that the disease is caused by aberrations in key genes of the expansion of the human brain evolution.
To test this hypothesis, an international team led by evolutionary biologist Philipp Khaitovich of Biological Sciences Institutes in China and the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, under Shanghai see how many genes linked to brain implicated in schizophrenia have undergone positive natural selection diverged from humans and chimpanzees from a common ancestor there are between 5 million and 7 million years.
First, the researchers studied the published databases of genes in the brain positively selected, which were classified into 22 categories according to function. They found that six categories included a high proportion of genes also involved in schizophrenia; genes in these six categories concern energy metabolism.
So the team focused its research on energy pathways in the brain. Using a technology called spectroscopy by nuclear magnetic resonance, the researchers measured levels of 21 metabolites key for nerve function in the brains of 10 deceased patients with schizophrenia and 12 normal human controls. Specifically, they studied an area of the prefrontal cortex involved in social cognition. Nine of metabolites, such as lactate, choline and acetate, showed significantly different levels - an upper portion, a lower portion - in schizophrenic and normal humans. This finding, the authors say, confirms previous studies that the brain's metabolism is "substantially changed" in schizophrenia.
The researchers then examined whether these new metabolites could be important in the evolution of the human brain. When they measured the concentrations in the same area in the brain of the chimpanzee, the team found that the differences between chimpanzees and normal human were much greater for those nine for the 12 non metabolites involved in schizophrenia, this suggesting that energy pathways involved in schizophrenia have also been modified by human evolution, the team reports in this week Genome Biology . And 40 genes involved in these new pathways related to schizophrenia also differ much between chimpanzees and humans that genes associated with the other 12.
The authors suggest that the human brain, which uses 20% of total body energy supply compared to 13% for non-human primates, is "very close to the limit of its metabolic capabilities." So close, they say, that small changes in energy-related genes could relatively easily cause mental problems.
"Schizophrenia can be the price we pay for our large brains and complex," said Jonathan Burns, a psychiatrist at R. Mandela School of Medicine in Durban, South Africa, called the findings "very exciting. "But Daniel Geschwind, neurogeneticist at the University of California, Los Angeles, warns that it is too early to link changes in metabolism to" any human cognitive specificity. "
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