Sex Differences in Co-Occurring Conditions of ASD

Background: Researchers have noted that as the overall number of autism spectrum disorders (ASDs) diagnoses has increased over the last few decades, a large difference in the number of female versus male diagnoses has also persisted, with males being 3-4 times more likely than females to be diagnosed with ASD.   Reasons for the large sex difference remain unclear; some have speculated that co-occurring conditions of ASDs may play an important role in determining the diagnosis of ASDs.  Examining the differences in co-occurring conditions between males and females with ASD may help to understand how these conditions affect the determination of ASD.  

Objectives: To compare numbers and types of co-occurring conditions in females versus males aged 3 – 17, with a current ASD diagnosis.

Methods: Using the US 2007 National Survey of Children’s Health dataset, two study groups were defined based on parent-reported data: 1) Males with a reported current ASD diagnosis (n = 753), and 2) Females with a reported current ASD diagnosis (n = 168).  Co-occurring conditions of interest included Attention Deficit Hyperactivity Disorder (ADHD), learning disability, developmental delay, speech problems, hearing problems, anxiety, depression, behavioral or conduct problems, and seizures or epilepsy.  Statistical analysis was carried out to examine the associations between child sex and the ASD co-occurring conditions.  Odds ratios (ORs) were computed by taking the odds of each co-occurring condition for the female group and comparing them against the odds of the condition for the male ASD group.  Analysis was performed using weighted data and accounted for the complex sampling procedures of the NSCH.

Results: As compared to males with a current ASD, females with a current ASD were 3.5 times (95% CI: 1.1-11.0) more likely to be African American (AA) and 2.4 times more likely to have a mother with education less than HS or HS (OR=2.4, 95% CI: 1.2-5.1).  Furthermore, boys with a current ASD were nearly 13 times more likely to have learning disability in the past and 5 times more likely to have a current, mild learning disability than girls. Girls were found to be 8 times more likely to have a reported speech problem in the past than boys after taking into account race, ethnicity, and maternal education.

Conclusions: Selective vulnerability of AA females to ASD, along with lower educational attainment of their mothers, if confirmed, may suggest differences in underlying risk including biological, nutritional, and/or environmental factors.  Greater risks for learning disabilities in males and speech problems in females with ASDs may relate to different patterns of sex-specific brain development. Studies that provide larger sample sizes are needed to further investigate sex differences in each co-occurring condition.