The clinical onset of autism appears to be preceded by two phases of brain growth abnormality, according to a study published in the July 16, 2003, issue of The Journal of the American Medical Association (JAMA).
"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 provide as background information in the article. "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, PhD, from the University of California, San Diego, La Jolla, California, and colleagues analyzed data, including head circumference (HC), body length and body weight measurements, from the medical records of 48 children with autism spectrum disorder (ASD) aged two to five years. The children had previously participated in magnetic resonance imaging (MRI) studies reporting age-related changes in the brain in autism.
Of the 48 participants with ASD, 15 (12 males and 3 females) had pediatric HC measurements at four age periods: birth, one to two months, three to five months, and six to 14 months, and were termed the longitudinal group. The remaining 33 children (29 males and 4 females) were termed the partial HC data group because they had HC measurements at birth and six to 14 months (n=7) and at birth only (n= 28). Two of the participants did not have a birth HC measurement, but did have an HC measurement at two weeks of age.
"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 write. "Specifically, we found a rapid and excessive increase in HC measurements, and therefore, presumably, brain size, beginning several months after birth. This abnormally accelerated rate of increase in HC measurements in infants with ASD was evident in comparisons to two nationally recognized normative databases, one 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 (CDC) averages of healthy infants to the 84th percentile in six to 14 months. This excessive increase occurred well before the typical onset of clinical behavioral symptoms," the authors report.
The researchers add that only six percent of the individual healthy infants in the longitudinal data showed accelerated HC growth trajectories from birth to six to 14 months; 59 percent of infants with autistic disorder showed these accelerated growth trajectories.
"Although an abnormally large increase in HC 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 write in conclusion.
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