Posserud MB, Solberg BS, Engeland A, et al. - The study observed a lower male to female ratio (MFR) and male prevalence ratio (PR) in adults than in children. Results imply the strong male predominance seen in childhood/clinical studies of autism spectrum disorder (ASD) diminishes in adult samples, possibly reflecting the influence of non-etiological factors such as later diagnosis in females, diagnostic biases, and diagnostic trends.

• Researchers recruited a total of 1,701,206 adults and 804,146 children, including 8,995 (0.5%) adults and 8056 (1.0%) children with ASD, 53,822 (3.2%) adults and 26,967 (3.4%) children with attention-deficit/hyperactivity disorder (ADHD) and 9,178 (0.5%) adults and 5,038 (0.6%) children with intellectual disability (ID).

• In children, the male to female ratio (MFR) for ASD was 3.67 and 2.57 was in adults, corresponding to a male PR in ASD of 1.54 (95% CI 1.53-1.56) and 1.41 (1.39-1.24), respectively.

• It was shown that comorbid ID reduced the MFR and the male PR in both adults and children, whereas comorbid ADHD significantly elevated the male PR in children.

• It has been reported that MFR and the population prevalence of ASD, ADHD and ID reduced from children to younger adults and yet further to older adults.