A new study suggests that boys and girls with autism have facial features that are characteristically more male than female. A wider forehead and a narrower midface are among several of the distinguishing traits. The findings, published in Scientific Reports, could provide evidence for a controversial theory that sees autism as the result of an "extreme male brain." 

Many conditions associated with brain development produce characteristic physical traits, and researchers from the University of Western Australia wondered if that tendency extended to the autism spectrum. They conducted a close analysis of facial compositions of 54 autistic and 54 non-autistic boys, as well as 20 autistic and 60 non-autistic girls. They chose to focus on preadolescent children based on the established evidence that sex hormone levels rise in puberty, giving way to normal changes in physical attributes, including those in the face. Focusing on the younger years meant whatever features they spotted would be more likely due to something other than aging. They closely examined the faces of the study participants for 11 facial features typically associated with a person's sex. 

The researchers found distinct facial similarities in boys and girls with autism compared to those in the control group. These included differences in the width of the alar base (or nostrils); height of the nose and upper lip; forehead width and height; right upper cheek height; and other subtle facial differences. In all of these, the participants with autism appeared closer to what's typically characterized as a male face. Other findings were in line with similar studies that have defined the autistic facial phenotype as an increased height and mouth width, and decreased midface height.

“Investigations into the facial structure of individuals of ASD [autism spectrum disorder] have the potential to reveal greater insights into the biological pathways leading to autism,” the researchers wrote in their study.

They also acknowledged some limits to their study. Data on prenatal testosterone exposure was not available, for example. In order to thoroughly establish the association between facial types and testosterone exposure, studies would need to be conducted that measured hormone levels in amniotic fluid or umbilical cord blood. The study also didn’t include data measuring testosterone levels at one month to three months old, a time in an infant’s development known as “mini-puberty” when hormone levels actually rise.  

The effort to identify a facial phenotype for autism could help improve clinical assessments, leading to diagnosis at a younger age and earlier interventions and treatment.

Proponents of extreme male brain theory may see this new study as supporting their claim. Coined in 2002 by Simon Baron-Cohen, now a director of the Autism Research Centre in Cambridge, England, the theory says that people with autism exhibit personality attributes and behaviors typically associated with the male gender, such as lack of empathy and rigid thinking. These common traits of people with autism, the theory asserts, are the result of higher exposure levels of male hormone testosterone during fetal development. Many experts have criticized the theory. 

Facial phenotyping is already used to identify and help diagnose other neurodevelopmental and genetic disorders such as Down Syndrome, characterized by upward-slanting, almond-shaped eyes, a flatter face and nose, and smaller ears. Fetal alcohol syndrome also produces distinctive facial features in a child that include an upturned nose, a thin upper lip and a small head circumference, among others, according to the journal American Family Physician.