Autism Spectrum - Epidemiology

Epidemiology

Reviews tend to estimate a prevalence of 6 per 1,000 for autism spectrum disorders as a whole, however prevalence rates vary for each of the developmental disorders in the spectrum. Autism prevalence has been estimated at 1-2 per 1,000, Asperger syndrome at roughly 0.6 per 1,000, childhood disintegrative disorder at 0.02 per 1,000, and PDD-NOS at 3.7 per 1,000. These rates are consistent across cultures and ethnic groups, as autism is considered a universal disorder.

While rates of autism spectrum disorders are consistent across cultures, they vary greatly by gender, with boys being affected far more frequently than girls. The average male-to-female ratio for ASDs is 4.2:1, affecting 1 in 70 males, but only 1 in 315 females. Females, however, are more likely to have associated cognitive impairment. Among those with an ASD and mental retardation, the sex ratio may be closer to 2:1. Prevalence differences might be accounted by gender differences in the expression of clinical symptoms, with females showing less atypical behaviors and, therefore, less likely to receive an ASD diagnosis.