Nature does nothing for free. Therefore, gene versions that cause diseases should also carry some kind of advantages - otherwise, selection would have eliminated them long ago. So what is the value of hereditary factors that cause schizophrenia?
Princeton, the late 1940s. The U.S. military is interested in a solitary but obviously highly gifted mathematics student. On a secret mission, he is to decipher espionage messages that Soviet agents have hidden daily his opponents are already hot on his heels: as unscrupulous doctors, they try to put him out cold in a mental hospital ...
What begins as an ordinary agent thriller turns more and more into a game of confusion. The film "A Beautiful Mind" tells the life story of mathematician John Nash, who was plagued by severe delusions - and in 1994 received the Nobel Prize in Economics for his groundbreaking work on game theory.
Genius and madness went hand in hand for Nash. But not everyone diagnosed with the typical symptoms of schizophrenia - delusions, hallucinations, and a disturbed sense of self - can hope for a Nobel Prize. On the contrary. Most of those affected can hardly developmentally because of their disturbed personality.
The cause of the nervous disorder is still not fully understood. However, there have long been indications that an inherited predisposition plays a not inconsiderable role. The risk of developing the disease is about forty percent if both parents suffer from schizophrenia. Among identical twins, it even rises to fifty percent.
But why are there gene versions that can lead to schizophrenia in the first place?
"It is paradoxical that schizophrenia is so common worldwide, even though it affects reproductive success"
After all, mental illness, which typically breaks out between puberty and age 30, doesn't exactly promote reproduction. So evolution should have eliminated such variants long ago. Nevertheless, about one percent of the population around the world still develops schizophrenia.
"It's kind of paradoxical that this disorder is so common worldwide, even though it affects health and reproductive success," agrees Steve Dorus of Britain's University of Bath. Together with Bernard Crespi from Canada's Simon Fraser University in Burnaby and Kyle Summers from the U.S. East Carolina University in Greenville, he tried to uncover the evolutionary secret of schizophrenia.
To do this, the researchers selected 76 DNA sequences suspected of increasing the risk of schizophrenia. In their analysis, they relied on the one hand on the HapMap project, which has collected the variations in the human genome. The "Haplotter" database contains gene versions for which positive selection is suspected, i.e. which - for whatever reason - have spread more widely in the human population. On the other hand, the "HomoloGene" database, which contains corresponding genes from various animal and plant species, proved helpful in enabling the researchers to compare the differences in individual hereditary factors between humans and apes.
The HapMap analysis crystallized 14 gene versions that appear to have been favored by evolution. The gene DTNBP1 (dystrobrevin-binding protein 1) stood out as particularly prominent. In comparison with other primate species, four genes emerged, with NRG1 (neuregulin 1) in particular standing out. And finally, the gene DISC1 (disrupted in schizophrenia 1), whose genetic influence in schizophrenia is undisputed, seems to enjoy special promotion by selection.
- In short, all three gene versions increase the risk of disease but are still subject to positive selection. They must therefore represent some advantage for the carrier. But which one?
- Dorus admits that this is the big question - "and we really haven't found a good answer yet.
- It is not unusual for disease-causing gene mutations to be beneficial. Sickle cell anemia, whose carriers are immune to malaria, is often cited as an example.
In the case of schizophrenia genes, the suspicion is that they could promote the creativity, imagination, and mental flexibility of those affected in return. The researchers still want to investigate whether this is the case. But perhaps the tendency to mental illness does indeed have its good sides - and sometimes even a Nobel Prize.