Brain volumes are significantly reduced in children who were born prematurely compared with children born at full-term, investigators report in the Journal of Pediatrics.

The specific effects of preterm birth depend on the child’s gender, however, with males being more susceptible to reductions in white matter, brain regions consisting of nerve fibers that look white under the microscope.

Up to 50 percent of very-low-birth-weight children have neurodevelopment handicaps and require special help in grade school, Dr. Allan L. Reiss and his team note in their paper. The reasons for these difficulties are not clear.

To investigate, Reiss, at Stanford University School of Medicine in California, and his associates obtained brain MRIs of 8-year-olds, including 65 who were born preterm and 31 who were born at term. Those born preterm weighed 600 to 1250 grams at birth.

Compared with the full-term subjects, boys and girls born preterm had reductions in gray matter, brain regions consisting of nerve bodies that look gray under the microscope. Preterm boys, but not preterm girls had significant reductions in white matter as well.

“The X chromosome is chock full of important genes for brain development and function; and having a second X chromosome may provide a partial layer of redundancy that helps protect girls,” Reiss explained in an interview with Reuters Health.

“It may be that there are genes on the X chromosome that help guide white matter development, or lay down…cells that will lead to white matter development later in life,” he added.

The authors point out that the gender differences in white matter were most evident in brain regions known to be involved in motor function, attention, emotion, reading and language. These brain structure differences in preterm males may partially explain boys’ greater likelihood of experiencing mental retardation, learning disabilities and autism.

However, only girls exhibited a link between the amount of gray matter and IQ test results.

The researchers plan to reexamine the subjects at ages 12 and 16. “That way we can see if this is a development phenomenon that will correct itself later in life,” Reiss added.

SOURCE: Journal of Pediatrics, August 2004.