Researchers are studying abnormal head growth in autism. In a study published in Pediatric Neurology, researchers hypothesized that accelerated head growth in the first two months of life could be an early indicator of increased risk of developing autism. Macrocephaly is a consistent physical finding in autistic adults, but it is not generally present at birth.
Although autism usually occurs before three years of age, it is often diagnosed later, sometimes not until the child is six years old. In a recent study of 251 autistic patients from 195 families, researchers found that 82 patients had family histories of autism while 113 did not. The study sample was 73 percent male (higher than the 3:1 ratio observed in the general autism population). Patients ranged in age from three to 21 years of age.
Nineteen percent of these patients had macrocephaly (head circumference greater than the 97th percentile), which is significantly higher than the three percent found in the general population. The group with macrocephaly and the 81 percent without it did not differ significantly on any of the diagnostic variables measuring social, communication and daily-living skills.
The researchers focused on the patients in the study whose medical records contained multiple head circumference measures. Twenty-eight (35 percent) showed an abnormal increase in head circumference of 25 or more percentile points between two consecutive measurements. Using data from those patients with repeated head circumference records between birth and one year of age, the researchers found that at or shortly after birth, autistic children display head circumference that is similar to that of the general population.
However, their analyses showed a significant number of individuals with accelerated head growth between birth-to-one-month and one-to-two-months of age. Seventeen individuals were measured at these two time periods, and 11 (65 percent) of them had head growth of more than 25 percentile points. According to these researchers, this sudden and excessive increase in head size between the first and second months of life in individuals with autism represents one of the earliest physical findings in the autism population and points to the need for investigations of this phenomenon. Regular observations of head circumference and its growth rate during the early stages of life may be important factors for identifying some children at risk for developing autism.
This study was limited because the data was acquired retrospectively from patient records whose reliability could not be confirmed, and early head circumference measurements were available for only a limited number of the individuals in the study. In addition, head measurements were not available for parents or unaffected siblings to rule out familial influences.
“Accelerated Head Growth in Early Development of Individuals with Autism”, Pediatric Neurology, Volume 32, Number 2, February 2005, pp. 102-108.
Published in ERN May/June 2005 Volume 18 Number 5