New research from an international team of scientists has found that a large body size—in addition to a large head—is associated with autism. While previous studies have consistently found that large head size, or macrocephaly, is more frequent in people with autism, the new study led by Antonio Persico, M.D. of the University "Campus Bio-Medico" in Rome found that a subset of people with autism had an abnormally large body size, or macrosomy. They also found that this group of individuals had a higher incidence of immune disorders. This research takes an important step toward defining subtypes within the autism spectrum, which will help pinpoint the cause of and appropriate treatments for autism.
Because each case of autism differs in symptom severity and presentation, autism may arise for different reasons in different people. To get a handle on this diversity, researchers have been working to identify subtypes, known as endophenotypes, in autism. In a study using subjects and data from the Autism Genetic Resource Exchange (AGRE) and funded in part by the former National Alliance for Autism Research and by Cure Autism Now, the researchers analyzed numerous morphological, clinical, and biochemical features of 241 people with autism to see if any features co-occurred with macrocephaly. In addition to finding that head circumference was highly correlated with height and weight, they found that macrocephaly was associated with more impaired adaptive behaviors, but with less impaired IQ scores and verbal language development. Most surprisingly, macrocephaly was also associated with immune disorders in either the patient or their family. This finding adds to the growing body of research pointing to a role for the immune system in autism.
Although the associations between head circumference, height, and weight in autism are only correlations and do not indicate that one causes the other, their convergence in this study potentially identifies a "macrosomic" endophenotype. People with this endophenotype may have a similar cause for their autism, and future research could test whether they share similar genetic or exposure anomalies. Thus, recognizing the endophenotypes in autism is critical for understanding the origins of autism and for designing valuable treatments.