Depression, schizophrenia, obsessive-compulsive behavior, psychosis, autism – the diseases that can affect our soul are many and varied. For a long time, researchers have been debating how much is genetic. Now researchers have scanned the genomes of more than 720,000.000 people. 490.000 of them were healthy controls, plus more than 230 000 people who had at least one of.000 people who suffered from at least one of eight mental disorders.
The result: apparently, the individual disorders have more in common genetically than the psychiatric diagnostic pigeonholes previously suggested, because there is no single depression or schizophrenia gene. Individual gene variants each make tiny contributions to driving up risk of mental disorder. The researchers found numerous single nucleotide polymorphisms (SNPs) that are associated with several psychiatric disorders.
To what extent are genes to blame and to what extent is the environment to blame??
But scientists are still unable to answer one important question: How much of the disease is due to genes and how much is due to the environment?? For example, schizophrenia: All gene variants associated with schizophrenia together currently explain only about 20 percent of the differences between sick and healthy subjects. But according to twin studies, the heritability is up to 80 percent. So where is the remaining 60 percent hidden??
Science offers several explanations for this discrepancy. One possibility is that the twin studies are based on false amptions and are misleading. However, psychobiologist Turhan Canli of Stony Brook University sees another possibility for why genetic studies have so far been unable to find a full explanation for the heritability of mental disorders. Genetic analyses have simply excluded large areas of human DNA from the study. He is thinking primarily of the approximately eight percent of our DNA that actually has no place there: Genes and gene fragments of viruses, or more precisely, human endogenous retroviruses. They are in our genome because our ancestors were infected with them millions of years ago. The pathogens have taken their chance and irrevocably inscribed themselves in the genome of their host.
Viruses provide clues
Researchers suspect retroviruses are a link between environmental factors such as infections, lifestyle or stress and the long-term misregulation of risk genes for mental disorders. Various studies show how these retrovirus gene fragments could influence mental suffering – and in the neighborhood of some human endogenous retroviruses lie, of all things, the genes known to be risk factors for schizophrenia.