Researchers in two large-scale multinational studies have found that rare genetic changes are associated with an increased risk of schizophrenia.

The International Schizophrenia Consortium studied the genomes of 3,391 patients with schizophrenia, looking for a specific type of genetic error called a “copy number variation (CNV),” in which a section of the genome has been deleted or duplicated. In the other study, the SCENE consortium cataloged all the CNVs between 15,000 parents and their children and looked for matches with the CNVs of over 4,600 schizophrenia patients.

Both studies found genetic deletions in chromosomes 1, 15 and 22. These deletions are associated with a greatly increased risk of schizophrenia.

Schizophrenia affects around 1 in every 100 people at some point during their lives. Genetic factors are thought to account for more than 70% of cases.