Patients who have a first­-degree relative with schizophrenia are eight times more likely to develop the disorder compared with those with no family history, a meta-analysis shows.

Researchers from the Prince of Wales Clinical School at UNSW Sydney say their findings will improve the accuracy of risk communication to patients and could even inform a ‘vulnerability index’.

Their meta-analysis is the first to quantify the familial risk of schizophrenia, drawing on data from 19 cohort and case-control studies involving 4875 at-risk relatives and more than 5000 healthy control relatives.

The risk of developing the condition increased to 11-fold when there were two first-degree relatives with schizophrenia. However, only two studies looked at the risks of having two relatives with the disorder.