Boys are 4 times more likely to be diagnosed with ASD than girls. One possible explanation is that most ASD research focuses on males and excludes female subjects, and as a result, the symptoms and mechanisms of ASD are poorly understood in girls. Girls are also prone to engage in “camouflaging” their autism symptoms. This study aimed to change that by investigating the effects of oxytocin (OT) and arginine vasopressin (AVP) on several behavioral symptoms of ASD in both boys and girls, including social behavior, language, repetitive behavior, and internalizing symptoms. OT and AVP are two neuropeptides (protein hormones that act on the brain) that have recently gained attention in ASD research due to their roles in facilitating prosocial behavior and are being studied as possible biomarkers of ASD.
The researchers compared blood plasma levels of OT and AVP among 40 individuals with ASD (19 girls, 21 boys) and 35 neurotypical individuals (16 girls, 19 boys), all of whom were between the ages of 8 and 18. They found that for both ASD and neurotypical subjects, girls had higher levels of OT than boys, and boys had higher levels of AVP than girls. Surprisingly, they found that these neuropeptides had different effects on boys and girls. Although OT is commonly thought of as a social hormone, higher blood plasma OT levels in girls were associated with greater anxiety in girls, but not in boys. Meanwhile, higher AVP levels were found to be associated with greater anxiety in boys, but not in girls. In girls, higher AVP levels were associated with higher levels of restricted and repetitive behavior, while the opposite was true in boys (albeit the correlation was nonsignificant for boys). For both boys and girls, higher OT levels were associated with greater social language.
This study’s findings that higher plasma OT levels were associated with higher anxiety in girls is consistent with previous studies that have shown plasma OT to be a biomarker of anxiety and depression in women. Previously, lower ASD diagnoses in girls have been attributed to higher OT levels in girls that “protect” them against expressing ASD symptoms, but the researchers of this study argue that all OT in the body may not have the same effect and should be studied more carefully, especially in girls. Girls with autism experience depression at a rate from 50-80% and are three times more likely to commit suicide than boys with autism.
Overall, the sexually dimorphic effects of two hormones, OT and AVP, proves the importance of including girls in ASD research and not extrapolating all ASD symptoms to all genders and different demographics. Doing so can hopefully help us better recognize how ASD manifests itself in girls, which will not only help us better diagnose and work with them, but also inform more accurate research in the future.
Miller, M., K. L. Bales, S. L. Taylor, J. Yoon, C. M. Hostetler, C. S. Carter, and M. Solomon. “Oxytocin and Vasopressin in Children and Adolescents With Autism Spectrum Disorders: Sex Differences and Associations With Symptoms.” Autism Research, 2013, vol. 6, pp. 91-102.