Advanced Reading: Schizophrenia Research on Risk Factors

Highlights of the International Congress on Schizophrenia Research

Randall F. White, MD; Michael Compton, MD

The International Congress on Schizophrenia Research (ICSR) took place in Savannah, Georgia, from April 2 to 6, 2005. Researchers from around the world presented the latest findings on etiology, epidemiology, and treatment of chronic psychotic illness.

Risk Factors for Schizophrenia

Recent research regarding what factors contribute to the development of schizophrenia was discussed during a symposium on the first day of the 2005 ICSR.^[1] Vera Morgan, MSocSc, of the Department of Psychiatry and Behavioural Science, University of Western Australia, Perth, Australia, said retrospective studies show that adverse obstetrical events increase risk for schizophrenia in offspring 2- to 7-fold. Having a parent with schizophrenia increases this risk by about 13-fold. She described a population-based study in Western Australia of 382 mothers with schizophrenia, 1449 with mood disorders, and 1831 with no mental disorder who gave birth between 1980 and 1992. Among the women with schizophrenia, placental abruption, antepartum hemorrhage, and side effects of street drugs were more common compared with women with mood disorders. Furthermore, ventricular septal defect, other cardiovascular defects, and minor physical anomalies were more common among the infants of women with schizophrenia compared with those of the women with mood disorders.^[2] According to Dr. Morgan, this research shows that women with schizophrenia have a higher risk of obstetrical complications and of more physical anomalies in their infants, suggesting a possible interaction of genetic and environmental factors in the etiology of the disease.

Jane Boydell, MD, of the Institute of Psychiatry, London, England, said that prior research shows a doubling of the incidence of psychosis and schizophrenia in South London from 1965 to 1999.^[3,4] Given established epidemiologic work implicating cannabis use in adolescence as a risk factor for schizophrenia, an increase in cannabis use in the United Kingdom over the same time period raised the question of its role in schizophrenia incidence in South London. In a retrospective study using the Camberwell Psychosis Database, she and her collaborators studied 1150 patients who presented with psychosis over 7 periods from 1965 to 1999 and assessed the use of cannabis in the prior year among those with schizophrenia, those with mania, and those with other disorders. They found that cannabis use disproportionately increased among those with schizophrenia compared with patients who had other psychiatric disorders, from 8% in those from the first time period to 37% in the last. Furthermore, cannabis use increased in each successive period. Cannabis users had a younger age of onset of psychosis and were more likely to be male. Dr. Boydell said that these findings provide indirect evidence that cannabis may play a causal role in schizophrenia.

Carsten Pedersen, MSc, of the National Centre for Register-Based Research, Aarhus University, Aarhus, Denmark, said that being born and raised in a city is a well-known risk factor for schizophrenia.^[5] In an attempt to further explore this, he and his colleagues examined urban-born probands with schizophrenia who had a rural-born older sibling, indicating that the family had moved from the country to the city before the birth of the proband. For comparison, they examined families with both proband and older sibling urban-born, and families with both proband and sibling rural-born. They adjusted for household moves because prior research indicates that the number of moves during childhood also correlates with risk.

They found that urban birth of the proband and of the older sibling each contributed independently to the proband's risk of schizophrenia. Dr. Pedersen said this indicates that "city families" are at increased risk for producing offspring with schizophrenia, which could be a risk factor in addition to whether a given individual is born in an urban or rural place.