Poor cognitive performance has long been considered a risk factor for schizophrenia. A new study refines this idea by showing that it is actually a person's poor cognitive performance relative to his or her family members that is associated with a higher risk of developing the disorder. The study—which includes nearly one million Swedish individuals—was conducted by Foundation Scientific Council Member & 1995 Lieber Prizewinner, Kenneth S. Kendler, M.D. of Virginia Commonwealth University, in collaboration with Kristina Sundquist, Henrik Ohlsson, and colleagues at Lund University in Sweden. A paper describing the study was published online in JAMA Psychiatry on March 30, 2016.

Dr. Kendler and colleagues took advantage of the extensive data included in Sweden's population registers. Their first dataset included 996,886 people born in Sweden between 1972 and 1990 who had a school record at age 16. The researchers used the data about the educational status of each individual's parents as well as the school achievement of at least one cousin and sibling to create a variable that they called Familial Cognitive Aptitude (FCA). They used the Swedish Hospital Discharge Register and the Swedish Outpatient Register to determine which of the people in this cohort would go on to be diagnosed with schizophrenia or bipolar disorder.

"We found that the risk for schizophrenia was strongly predicted by the deviation of school achievement from the familial cognitive aptitude, but not at all by the absolute level of school achievement," say Drs. Sundquist and Ohlsson.

While this study does not provide information about when these cognitive deficits first showed up in the people who would go on to be diagnosed with schizophrenia, the results suggest that looking at cognitive performance in individuals as well as their families may help identify people who may go on to develop the disorder so that they can be offered treatment early on.

One potential future research avenue raised by these results is determining whether, and to what extent, significantly differing in cognitive achievement relative to one's family is a stressor or risk factor that puts someone at increased risk for developing the disorder.

Takeaway: A study based on data about 1 million Swedes demonstrated that a young person’s deviation from his or her family’s cognitive aptitude, as measured by school performance of several close relatives, predicted risk level for developing schizophrenia.