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. …