One in 68 children is diagnosed with an autism spectrum disorder. That figure jumps to one in 42 for males. A contributing factor may be that ASD and fragile X syndrome are often comorbid, and as a sex-linked disease, fragile X syndrome affects males more often than females. However, another factor that may contribute to ASD being more common in males is bias in diagnosis.
The article Autism - It’s Different in Girls by Maia Szalavitz claims that the criteria for diagnosing ASD are almost entirely based on data derived from studies of boys. Researcher Kevin Pelphrey believes that many girls and women may be missed in these diagnoses because autism symptoms may manifest differently based on sex. A study of upwards of 15,000 twins showed that if boys and girls have similar levels of traits that would typically indicate autism, girls would have to additionally have an intellectual disability or significant behavioral problems to be diagnosed as autistic, whereas boys would not. Pelphrey has found in his own research that brain analyses of autistic girls are quite comparable to the brain analyses of developmentally normal boys, appearing normal when compared to an autistic boy’s brain, but lacking in some activity when compared with the brain of a developmentally normal girl.
The article also suggests that many females may be missed in diagnoses because they have a greater ability to hide their symptoms, learning from other behavior, observing, and acting in ways according to social norms to mask their own autistic symptoms. In autistic females, diagnoses often occurs more based on internal feelings and experiences expressed by the patient rather than on outward presentation.
Dr. Maggie Guy has dedicated her time to taking EEGs of infants at increased risk of autism, as they are too young for a formal diagnosis. She looked at event related potentials when infants were presented with different stimuli - particularly faces. Results showed infants who were siblings of children diagnosed with autism had a diminished response in the N290 ERP component, which is strongly associated with facial processing. Interestingly, infants with fragile X syndrome showed increased N290 amplitude, however they also showed the same pattern of increased amplitude in response to toys, while other groups did not.
The idea of autism effecting the sexes differently may tie heavily into Dr. Guy’s work, as her sample was 74% male. The fragile X group was the least gender biased, with 8 out of 15 infants being male, so this may actually make sense of the increased N290 amplitude. If it is true that the autistic female brain is more similar to a developmentally normal male brain of the same age group, this could skew the results towards normalcy, hence give an increased amplitude in the ERP when compared to siblings of children with autism.
Perhaps future directions could discriminate between male and female data to give a better picture of how typically-autistic traits — such as decreased activity in response to human faces — differ across the sexes. Using Dr. Guy’s experimental set up on a population that included both diagnosed autistic and developmentally normal children of both sexes could help lead to a better understanding of how ASD differ with gender, and could give better insight on diagnoses, perhaps even contributing to the research of whether ASD really is simply more common in males, or if it just manifests differently.
References:
Guy, Maggie W., et al. “Neural Correlates of Face Processing in Etiologically-Distinct 12-Month-Old Infants at High-Risk of Autism Spectrum Disorder.” Developmental Cognitive Neuroscience, vol. 29, 2018, pp. 61–71., doi:10.1016/j.dcn.2017.03.002.
Szalavitz, Maia. “Autism--It's Different in Girls.” Scientific American, 1 Mar. 2016, www.scientificamerican.com/article/autism-it-s-different-in-girls/.
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