Children with autism often have siblings with language delays and other, more subtle behaviors that are characteristic of the autistic spectrum. The Interactive Autism Network conducted a study of more than 1,200 families. The Interactive Autism Network is an online research registry dedicated to gathering information about autism.
NPR’s Jon Hamilton writes that findings suggest “the genes behind autism in one child may contribute to less serious problems in that child’s siblings.”
The study’s lead author, Dr. John N. Constantino, of Washington University School of Medicine, stated, “Mild symptoms, called quantitative traits, may be confounding studies that compare children with autism to their siblings. Researchers presume one child is affected, and the other is not, but our findings suggest that although one child may have autism and the other does not, it’s very possible both children are affected to some degree by genes that contribute to autism” (Science Daily). These quantitative traits are “not strong enough to provoke a diagnosis of autism,” but they appear to be more present in siblings of children with autism than they are in the general population (Science Daily).Eleven percent of families with a child with autism also had a second child that had been diagnosed with the disorder. Additionally, one in five siblings, or 20%, who did not have autism “had been diagnosed with language delay or speech problems early in life” (Hamilton). Almost half of those siblings “had speech qualities associated with autism” (Hamilton). According to Rebecca Landa, director of the Center for Autism and Related Disorders at the Kennedy Krieger Institute in Baltimore, these speech qualities include, among other things, “a lack of intonation, a familure to emphasize important words or a staccato delivery of sentences” (Hamilton).
Landa adds, “Not only autism, but autistic traits can run in families. If you have one child with autism, it’s important to monitor any other children from infancy.” If there appears to be a problem, that child needs to be professionally evaluated.
The significance of this study cannot be overstated. Autism is a spectrum disorder; people can be highly affected or not. Dr. Constantino reiterates, “It’s not an all-or-nothing condition.” Siblings of children with autism seem to have genetic susceptibility and subtle autistic traits. An accumulation of quantitative traits provokes a diagnosis of autism; subtler traits of the disorder suggest genetic inheritability of not only autism but its hallmark behaviors.