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Dyslexia risk linked to summer births.

A new study suggests that children born in summer months stand the greatest chance of developing dyslexia, a reading disorder that may afflict up to 9 percent of children in the United States.

This seasonal pattern may result from the exposure of women in the second trimester of pregnancy to influenza or other viral diseases during late winter, theorize Richard Livingston, a psychiatrist at the University of Arkansas for Medical Sciences in Little Rock, and his colleagues. Viruses may subtly derail the paths traveled by brain cells during that crucial stage of fetal development, the researchers maintain.

The finding of seasonal clustering requires confirmation by other investigators, but it coincides with evidence implicating viruses and other sources of potential harm to the fetal brain as contributing causes of schizophrenia (SN: 9/19/87, p. 180), autism, mental retardation, and hyperactivity.

"Second-trimester viral exposure is presently the most attractive hypothesis to account for a seasonal birth pattern in dyslexia," the researchers conclude in the May JOURNAL OF THE AMERICAN ACADEMY OF CHILD AND ADOLESCENT PSYCHIATRY.

However, brain changes that lie behind dyslexia should prove "significantly more discreet" than those presumed to foster a severe mental disorder such as schizophrenia, Livingston notes.

Livingston and his co-workers reviewed data on 585 boys born between 1948 and 1970 who were referred to a university psychiatric clinic, often for behavior or learning problems. Boys ranged in age from age 9 to their early 20s. A total of 173 suffered from dyslexia, defined as a reading score on standard tests falling at least two years behind the expected level despite a normal IQ.

Too few dyslexic girls attended the clinic to allow for an analysis of their risk of developing the disorder.

Overall, boys born in May, June, or July displayed more than twice the risk of developing dyslexia as boys born in any other month, the investigators found. Births in these three months accounted for 40 percent of all instances of dyslexia, Livingston says.

The risk of being born dyslexic peaked during particular spans of years, the psychiatrists note. The most pronounced risk was from 1950 to 1954, when summer births accounted for seven in 10 cases of dyslexia. A review of Arkansas state health records indicates that the greatest number of cases of influenza and measles occurred in the years during which the most dyslexics in the sample were born, Livingston says.

Complications other than viral exposure may disturb fetal brain development and foster dyslexia among children born in non-summer months, he adds. For instance, compared with summer-born dyslexics in the Arkansas sample, dyslexic boys born from November to January experienced substantially more premature births, size abnormalities at birth, and birth-related head injuries.

"I suspect different types of early brain insults can cause dyslexia," Livingston says.
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Title Annotation:researchers think a mother's exposure to viruses during winter months may cause child to develop dyslexia
Author:Bower, Bruce
Publication:Science News
Date:May 1, 1993
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