Do risk factors for autism spectrum disorders affect gender representation?

To examine the M:F ratio in several known risk factors to demonstrate insights regarding autism spectrum disorders (ASD) etiology and sex. The study included 615 participants aged 18 months to 18 years age (mean = 49.8 months, SD = 28.4 months) diagnosed with ASD. Cognitive, adaptive and assessment of ASD were obtained using standardized tests. Detailed birth, familial, medical and developmental histories were obtained from the parents. Risk factors included ASD in the family (having a first-order family member with ASD); advanced maternal age (≥35 years); advanced paternal age (≥38 years); birth order (first-born versus third-born); low birth weight (LBW) (<2500 g); prematurity (gestational age <36 weeks). The M:F ratio (4.4:1) in the LBW group was lower than the M:F ratio (7.1:1) in the >2500 g group; however the difference showed only a statistical trend. No significant differences in M:F ratio were found between the ASD groups with and without the other examined risk factors. It is possible that the absence of a major association between most of the examined risk factors and sex representation points to the relatively minor role of these risk factors in ASD.