Associations between co-occurring conditions and age of autism diagnosis: Implications for mental health training and adult autism research.

Adult autism studies are increasingly comprised of later-diagnosed adults, yet little is known about how these adults compare to those diagnosed earlier in life. The present study examines medical and psychiatric conditions endorsed by autistic adults and documents differences between those diagnosed with ASD in childhood versus adulthood, as well as across age groups and sex at birth. 4657 legally independent adults (ages 18-85, M = 33.4 years) with professional ASD diagnoses who completed a medical questionnaire were drawn from the Simons Powering Autism Research Knowledge (SPARK) study. Chi square analyses, t-tests, and logistic regressions were used to compare medical and psychiatric conditions between age groups, sex at birth and adults diagnosed in childhood (before age 21) versus adulthood (at or after 21 years). Overall number of conditions endorsed as being diagnosed by a professional was high, with an average of 1.69 (SD = 2.01) medical or developmental and 2.98 (SD = 2.29) psychiatric conditions reported across the sample. Females were more likely to endorse psychiatric conditions (OR = 1.68). Adult-diagnosed adults were more likely to endorse psychiatric conditions (OR = 2.71) and reported more lifetime psychiatric diagnoses (M = 3.15, SD = 2.23) than their childhood-diagnosed counterparts (M = 2.81, SD = 2.33). These findings underscore the need for research to better understand and treat co-occurring psychiatric conditions in autistic adults and report and consider the age of diagnosis in adult autism samples. Moreover, results suggest it is imperative that mental health professionals receive autism training to promote accurate differential diagnosis and equitable access to mental health care for autistic adults with co-occurring psychiatric conditions.