December 18, 2013. For most people with schizophrenia, the cause of their illness is thought to be a complicated mixture of many genetic and environmental factors. For a small number, however, duplicated or deleted regions of genetic material on chromosomes seem to have an outsized effect: People with these missing or extra bits of DNA have a very high risk of developing the illness. Not everyone who “carries” the DNA changes gets schizophrenia, but a new study published online December 18, 2013, in Nature shows that carriers without the illness have similar, though milder, versions of the cognitive problems (such as difficulty paying attention or remembering details) that afflict people with schizophrenia.
Kari Stefansson, of deCODE genetics/Amgen in Reykjavík, Iceland, and Andreas Meyer-Lindenberg at the University of Heidelberg, Mannheim, Germany, and their colleagues looked at the genomes of over 100,000 adults from Iceland to identify those with chromosomal changes that have been linked to schizophrenia or autism, or, in several cases, with both disorders. The researchers excluded any people with diagnoses of schizophrenia, autism, or similar illnesses to form a group of “carrier controls” that they then compared to control and schizophrenia groups (both of whom lacked the chromosomal abnormalities). As expected, the researchers found that people with schizophrenia performed worse on cognitive tests than controls lacking a genetic abnormality. But surprisingly, carrier controls were also impaired, though not as much as people with the illness. The findings suggest that cognitive impairments are a fundamental defect in schizophrenia, write the authors, and are present long before psychotic symptoms develop. (For more details, see the related news story.)—Allison A. Curley.