Boys with autism and autism spectrum disorder had higher levels of hormones involved with growth in comparison to boys who do not have autism, reported researchers from the National Institutes of Health, the Centers for Disease Control and Prevention, the Cincinnati Children's Hospital and the University Of Cincinnati College Of Medicine.
The researchers believe that the higher hormone levels might explain the greater head circumference seen in many children with autism. Earlier studies had reported that many children with autism have very rapid head growth in early life, leading to a proportionately larger head circumference than children who do not have autism.
The researchers found that, in addition to a larger head circumference, the boys with autism and autism spectrum disorder who took part in the current study were heavier than boys without these conditions.
"The study authors have uncovered a promising new lead in the quest to understand autism," said Duane Alexander, M.D., Director of the National Institute of Child Health and Human Development, the NIH institute that funded the study. "Future research will determine whether the higher hormone levels the researchers observed are related to abnormal head growth as well as to other features of autism."
Autism is a complex developmental disorder that includes problems with social interaction and communication. The term autism spectrum disorder (ASD) refers to individuals who have a less severe form of autism.
The study was published on line in Clinical Endocrinology.
The researchers compared the height, weight, head circumference and levels of growth-related hormones to growth and maturation in 71 boys with autism and with ASD to a group of 59 boys who did not have these conditions.
The investigators found that the boys with autism had higher levels of two hormones that directly regulate growth (insulin-like growth factors 1 and 2). These growth-related hormones stimulate cellular growth. The researchers did not measure the boys' levels of human growth hormone, which for technical reasons is difficult to evaluate.
The boys with autism also had higher levels of other hormones related to growth, such as insulin-like growth factor binding protein and growth hormone binding protein.
In addition to greater head circumference, the boys with autism and those with autism spectrum disorders weighed more and had a higher body mass index (BMI). BMI is a ratio of a person's weight and height. A higher BMI often indicates that a person is overweight or obese. The boys' higher BMI may be related to their higher hormone levels, said the study's principal investigator, NICHD's James L. Mills, M.D., a senior investigator in the Division of Epidemiology, Statistics and Prevention Research's Epidemiology Branch. Dr. Mills and his coworkers also found that there was no difference in height between the two groups of boys.
The levels of growth-related hormones were significantly higher in the boys with autism even after the researchers compensated for the fact that higher levels of these hormones would be expected in children with a greater BMI.
"The higher growth-related hormone levels are not a result of the boys with autism simply being heavier," said Dr. Mills.
While it has long been noted that many children with autism have a larger head circumference than other children, few studies have investigated whether these children are also taller and heavier, Dr. Mills added.
Researchers analyzed medical records and blood samples from 71 boys diagnosed with autism and ASD who were patients at Cincinnati Children's Hospital Medical Center from March 2002 to February 2004. The researchers compared the information on the boys with autism and autism spectrum disorders to other boys treated for other conditions at the hospital and who do not have autism. Children with conditions that may have affected their growth - such as being born severely premature, long-term illness, or the genetic condition Fragile X were not included in the study. Girls are much less likely to develop autism than are boys, and the researchers were unable to recruit a sufficient number of girls with autism to participate in the study.
Dr. Mills explained that the bone age of the boys with autism - the bone development assessed by taking X-rays and comparing the size and shape of the bones to similarly-aged children - were not more advanced in the group of boys with autism. For this reason, Dr. Mills and his coworkers ruled out the possibility that they were merely maturing more rapidly than were the other boys.
Dr. Mills said that future studies could investigate whether the higher levels of growth hormones seen in children with autism could be directly related to the development of the condition itself.