Schizophrenia baffles most; people often associate the disease with a loose conglomeration of symptoms such as hearing voices and hallucinations. Even the word schizophrenia is misleading—it roughly translates to the splitting of the mind. Researchers have been struggling to understand the disease, which only affects 1 percent of the U.S. population, but is one of the most debilitating mental illnesses.

Three new studies in the journal Nature have shown that a few small changes in our genome can cause this disorder and many people in the population carry the anomalies.

The authors scanned the genomes of 2,663 people with schizophrenia and 13,498 without it, looking for single nucleotide polymorphisms (SNP). SNPs are genetic variations present in most people, but more commonly found in people with schizophrenia. The researchers discovered that people with schizophrenia had many deviations on their genes in the Major Histocompatibility Complex (MHC), a cluster of genes responsible for controlling immune reactions.

Researchers say this discovery is particularly intriguing because many people in the general population share the same variations on their MHC genes, but not everyone develops schizophrenia. They even speculate that if a mother becomes ill while pregnant, this can cause the genes to mutate from a normal to abnormal gene.

The researchers also found variations on NRGN and TCF4, which affects some of the pathways that control brain development, memory, and cognition. "It's a disease of thoughts and emotions, the two functions of the brain that define us as a species and define us as individuals," said Kari Stefansson, CEO of the Icelandic company deCODE Genetics and one of the investigators.

"Common variants conferring risk of schizophrenia," Nature.

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