Accelerated brain growth between birth and roughly 6 to 14 months of age may predict clinical onset of autism spectrum disorder, according to an article in the July 16th issue of the Journal of the American Medical Association.

"Behavioral signs and symptoms during the second and third years of life, including delayed speech, unusual social and emotional reactions, and poor attention to and exploration of the environment, raise warnings that a child might have autism," the authors wrote in their introduction. "Autism is a neurobiological disorder, and neurobiological abnormalities must necessarily precede the first behavioral expressions of the disorder. However, such neurobiological early warning signs have not yet been discovered for autism."

Eric Courchesne, Ph.D., and his American colleagues analyzed data including head circumference and body length and body weight measurements for 48 children with autism spectrum disorder aged 2 to 5 years. The children had previously participated in magnetic resonance imaging studies that found age-related changes in the brain in children with autism.

Of the 48 children whose illness fell on the autism spectrum, 15 (12 males and 3 females) had pediatric head circumference measurements at 4 age periods: birth, 1-2 months, 3-5 months, and 6-14 months. They were collectively termed the longitudinal group. The remaining 33 children (29 males and 4 females) were termed the partial head circumference data group because they had measurements at birth and 6-14 months (7 children) or at birth only (28 children). Two of the 48 children did not have a birth measurement, but did have measurement of head circumference at age 2 weeks.

"This is the first study to our knowledge to find a potential early warning biological sign for autism and to link it to a later brain abnormality," the authors wrote. "Specifically, we found a rapid and excessive increase in head circumference measurements, and therefore, presumably, brain size, beginning several months after birth. This abnormally accelerated rate of increase in head circumference measurements in infants with autism spectrum disorder was evident in comparisons to 2 nationally recognized normative databases, 1 a national cross-sectional survey and the other a longitudinal study of growth patterns in healthy infants. In our study, head size increased from the 25th percentile based on the Centers for Disease Control and Prevention averages of healthy infants to the 84th percentile in 6 to 14 months. This excessive increase occurred well before the typical onset of clinical behavioral symptoms."

The researchers added that only 6 percent of the individual healthy infants in the longitudinal data showed accelerated growth trajectories in head circumference from birth to 6 to 14 months; 59 percent of infants with autistic disorder showed these accelerated growth trajectories.

"Although an abnormally large increase in head circumference in an infant cannot be viewed as a certain and unique marker of autism, it nonetheless does appear to be an important signal that an infant is at significantly heightened risk for the disorder," the authors concluded.

In an accompanying editorial, Janet E. Lainhart, M.D., wrote "In this issue of The Journal, Courchesne and colleagues provide additional information about abnormalities of head size and brain volume in autism."

"Courchesne et al conclude that increased rate of head circumference growth during infancy appears to indicate an increased risk for autism. However, risk requires the establishment of precedence. If increased rate of head growth in infancy is a risk factor for autism, it must precede the onset of the disorder. It is not yet clear if this is the case. ... Increased rate of head growth during infancy in autism may be an important concomitant or correlate of autism (that is, a physical symptom of the disorder) rather than a risk marker."

"The study by Courchesne et al provides important direction for what studies need to be performed next. The findings should be confirmed in a larger sample of individuals with autism. In addition, brain growth in infancy and the relationship between patterns of early head and brain growth and the early course of autism need to be studied. It is premature to conclude that increased rate of head growth is a universal feature of autism."