Summer Births Linked to Type of Schizophrenia

Oct. 4, 2004 -- People with "deficit schizophrenia" -- a relatively severe form of the disease with symptoms of social withdrawal, depression, apathy, and lack of motivation or interest -- are more likely to be born in the summer months, a new study shows.

Schizophrenia is a severe mental disorder that affects about 1% of the population. The exact cause is unknown, but it's likely caused by a combination of factors such as heredity, problems in the way the brain develops before birth, and problems experienced during the mother's pregnancy that may affect the development of the unborn baby's brain and nervous system (the network of nerves in the body), such as exposure to a virus.

Schizophrenia has long been linked to birth during winter months; this type of schizophrenia involves hallucinations, incoherent thinking, and delusions - the so called "positive" symptoms that are "added" to the affected person's personality.

Deficit schizophrenia -- the focus of this current study -- involves "negative" symptoms (those aspects of a personality that are "lost") such as blunted speech and expression, lack of emotional response, lack of interest in socializing, and poor eye contact. It's considered a more severe form of the illness, writes lead researcher Erick Messias, MD, MPH, with the National Institutes of Health.

His paper appears in the current issue of Archives of General Psychiatry.

To look for more season-of-birth evidence and schizophrenia, Messias and his colleagues reviewed nine studies of 1,594 patients living in Ireland, England, Scotland, Spain, and the U.S.

Researchers found that more patients with deficit schizophrenia were born in June and July than in any other months.

Because studies have shown that schizophrenia is associated with birth in the winter, the researchers conclude that this subtype of the condition (deficit schizophrenia) arises from a different cause than non-deficit schizophrenia.

Messias and colleagues suggest that this new data will be useful in teasing out the genetic and environmental factors that may contribute to schizophrenia. Sunlight exposure, vitamin D, and infectious agents have all been proposed as possible explanations for this seasonal link, but no clear cause has been identified.