30093
Hypermasculinised Facial Structures in Brothers but Not Sisters of Autistic Children
Autism spectrum disorder (ASD) is diagnosed approximately three times more frequently in males than in females. One biologically-driven hypothesis suggests that the male prevalence in ASD may be influenced by the exposure to elevated concentrations of testosterone during pregnancy. During fetal development, the brain and the face evolve from the neural crest in synchrony. This has led to the speculation that facial structures may hold crucial information to further our understanding of atypical neurodevelopment in ASD. A recent study reported hypermasculinised facial structures of autistic boys and girls when compared to non-autistic children (Tan et al., 2017, Scientific Reports).
Twin and family studies have provided clear evidence that certain cognitive phenotypes associated with ASD, such as social difficulties, are highly heritable. In terms of facial structures, several studies have found familial factors to explain more than 70% of structural variations in faces; of which, familial factors accounted for 49% of the variations in facial masculinity in particular.
Objectives:
The present study aims to investigate whether masculinised facial features are present in full siblings of autistic children using 3D photogrammetry.
Methods:
Twenty-three boys (mean age=7.31 yrs, SD = 2.68) and 20 girls (mean age=6.95 yrs, SD = 2.76) who are non-autistic siblings of children with ASD were included in this study. Every sibling was age- and sex-matched with three typically-developing children without siblings with ASD (69 boys [mean age=7.39 yrs, SD = 2.51] and 60 girls [mean age=7.41 yrs, SD = 2.42]). Landmarks were placed on each 3D image to generate a set of linear and geodesic distances previously found to accurately differentiate between boys and girls of similar ages as those included in the current study. Using these distances, a continuous ‘gender score’ can be computed for each face to indicate the degree of facial masculinity. Behavioural information collected using Social Responsiveness Scale-2 (SRS-2) is available for 28 siblings (17 boys) and Children Communication Checklist-2 (CCC-2) is available for 24 siblings (14 boys).
Results:
Facial masculinity was significantly increased in the male siblings of autistic children compared to those of the male comparison group [t(90) = 2.92, p = .004, d = .70]. However, there was no difference in facial masculinity between female siblings and comparison group (p = .67). Using Spearman’s rank correlation coefficient, we found that facial masculinity was unrelated to scores on SRS-2 and CCC-2 when boys and girls were analysed together and separately.
Conclusions:
Tan et al. (2017) reported hypermasculinised facial structures in both boys and girls with ASD relative to a comparison group of non-autistic children. The current study found that hypermasculinised facial features were present only in male siblings of autistic children but not in female siblings. This study suggests the possibility that facial masculinity associated with ASD may be heritable only in boys but not in girls.