Profile of Girls Diagnosed with Autism Spectrum Disorder in a Clinical Setting

Background: Autism spectrum disorder (ASD) is estimated to be almost 5 times more common in boys than girls (Baio, 2014) and as such, what we know about the profile of ASD in girls lags far behind what is known about boys. Research has demonstrated greater cognitive impairment in girls (Frazier et al, 2014) and later age of diagnosis, which can delay the start of intervention (Kavanagh et al., 2013; Rynkiewicz et al., 2012).

Objectives: The purpose of this study is to analyze the characteristics of girls diagnosed with autism in a clinic setting, including age of diagnosis, rates of diagnosis, and cognitive and adaptive functioning. 

Methods: A record review was conducted of 1293 diagnostic evaluations conducted between 1/1/2012 and 9/30/2014 in an autism center serving a diverse population in Atlanta, GA. Children (ranging in age from 19 months to 16 years) were clinically referred and received a diagnostic interview prior to the assessment, confirming the presence of red flags for ASD. Diagnostic evaluations each included a developmental/cognitive measure (e.g., Mullen Scales of Early Learning, Differential Abilities Scale-Second Edition), adaptive measure (e.g. Vineland Adaptive Behavior Scales), and the Autism Diagnostic Observation Scale (ADOS or ADOS -II).

Results: Of the 1293 children who were evaluated, 824 received a diagnosis of ASD, and 108 (13%) of these were girls. There was no significant difference in age of first diagnosis based on gender (Girls M=50.77 months, SD =19.3; Boys M=54.2 months, SD=18.99).  Sixty-six percent of the boys evaluated met diagnostic criteria for ASD, whereas only 41% of the girls met diagnostic criteria. Thirty percent of girls had a nonverbal IQ that fell within the average to above average range (IQ > 85), while 28% had average to above average verbal IQ. Girls with average to above average verbal IQ had a significantly later average age of first diagnosis (M=60.28 months, SD=24.08) than those with delayed verbal scores (M=46.36 months, SD=15.35; t(56) = 2.42, p<.05), though this difference was not found with regard to nonverbal IQ.  Both verbal IQ and nonverbal IQ were positively correlated with the girls’ scores in adaptive communication, daily living skills, socialization and motor skills on the Vineland.

Conclusions: Findings highlight comparable age of diagnosis for boys and girls, a lower rate of diagnosis for girls than boys in a clinical setting, and a later age of diagnosis for girls with higher verbal IQ scores (5.0 years old) compared those with delayed verbal IQ (3.8 years). Thirty percent of girls had average to above average cognitive scores, which is lower than the 46% that has been shown in overall population studies of both boys and girls with autism (Baio, 2014). Higher cognitive scores were associated with better adaptive communication, daily living skills, socialization and motor skills. These findings underscore the importance of continued focus on girls with ASD, particularly those with higher functioning forms of ASD, who may be later to be identified and underrepresented in the literature.