Why are more males than females diagnosed with Autism Spectrum Disorder?

Written by: Brian Cechmanek

The prevalence of Autism Spectrum Disorder (ASD) is roughly 1 in 68 children, and is commonly reported with a 5:1 ratio of males to females with ASD (1 in 42 boys versus 1 in 189 girls) (CDC, 2014). While it is possible that this is an accurate sex difference in rates of ASD, sex differences in ASD have not been fully studied, opening the possibility that the way ASD is diagnosed creates some of this imbalance. One partial explanation for this bias is that males are diagnosed more often than females - or rather, that females with ASD are under-diagnosed. Madic-Maravic et al (2015) explored this potential explanation. 

To examine sex differences in diagnoses, low-functioning participants were separated into two groups: those with “typical autism”, and any other forms of ASD (Pervasive Developmental Disorders); “atypical autism”. Males were more frequently diagnosed with typical forms (83%), compared to females (56%). There were, however, no sex differences for ADI-R (social reciprocity, communication, restrictive repetitive stereotyped behaviours) scores. But, other studies have shown differences, particularly less restrictive repetitive stereotyped behaviours in female autistic participants (labelled “high functioning”) (Mandy et al, 2012). This could suggest that only female autistic participants (labelled ‘high-functioning’), show less restrictive repetitive stereotyped behaviours than boys.

This study found that females were more often diagnosed with other forms of ASD. These atypical forms may not always be as likely to be diagnosed, which means that in high-functioning groups, autism may be less likely to be diagnosed in females than in males. More specifically, this study showed that males tend to have a more predictable set of ‘clinical symptoms’, while females show more socialization and communication symptoms. 

A tautology is a logical truth by its own definition. In this case, clinical diagnosis of autism is based on clinical symptoms, which are determined by clinical definitions. If males with autism display more clinical symptoms, then by definition males will be diagnosed more than females. But when the set of symptoms used for clinical diagnosis evaluate certain symptoms more than others, such as restrictive repetitive and stereotyped behaviour (seen more in males) rather than communicative symptoms (seen more in females), we can see how a sex bias for diagnosis could occur. Further, use of the ADI-R (a parental survey of their child) for diagnosis, may be biased by restrictive repetitive and stereotyped behaviours being more apparent to the parent, than communicative symptoms. This hints that future work should examine the clinical classifications used to diagnose ASD, to ensure that females are not being (unintentionally) under-diagnosed. 

Reference:

Vanja Mandic-Maravic1, Milica Pejovic-Milovancevic1, Marija Mitkovic-Voncina1, Milutin Kostic1, Olivera Aleksic-Hil1, Jelena Radosavljev-Kircanski1, Teodora Mincic1 & Dusica Lecic-Tosevski1.Sex Differences in Autism Spectrum Disorders: Does Sex Moderate the Pathway from Clinical Symptoms to Adaptive Behavior. Sci Rep. 2015 May 19;5:10418. doi: 10.1038/srep10418. http://www.ncbi.nlm.nih.gov/pubmed/25988942