Studies at OTARC and elsewhere have shown that infants and toddlers show early signs of ASD, which can be observed from the first year of life. These are first characterized by a lack of attention to social stimuli, and usually progress into clearer ASD symptoms throughout toddlerhood and the pre-school years (Clifford & Dissanayake, 2008). Similarly, studies investigating the early development of restricted and repetitive behaviours (RRBs) in children with an ASD have highlighted that certain RRBs are present in toddlerhood, with others becoming more evident over time (Leekam et al., 2011). These early symptoms are now used for the early identification of ASD in infants and toddlers.
However, given that approximately four times more males than females are diagnosed with an Autism Spectrum Disorder (ASD), studies on ASD, including studies on the early signs of ASD and their later manifestation, typically include more boys than girls. As a consequence, identification and diagnosis is based primarily on what we know about boys with an ASD. The question then is whether the early signs and later manifestations of ASD are the same or different in girls and whether they may be at risk of mis- or under diagnosis, leading to the disproportion in diagnosis.
The research for my PhD (supervised by Professor Cheryl Dissanayake) was designed to find answers to these questions. I completed three studies.
- Study 1: I used data from developmental checklists of 60 boys and 18 girls who were diagnosed with ASD at 24-months as part of the Social Attention and Communication Study (Barbaaro & Dissanayake, 2010). The checklists had been completed by Maternal and Child Health nurses to chart early social interaction (SI) and vocal communication (VC) across three different time periods (Time 1, birth to 12 months; Time 2, 13 to 18-months; Time 3, 19 to 24 months). I found that the SI and VC behaviours were similar in boys and girls, with both boys and girls engaging to a similar extend in SI behaviours, such as smiling, pointing and eye contact, and VC behaviours such as babbling, obeying instructions and verbalising needs. Of particular interest was that both boys and girls showed a decrease in SI and VC behaviours from the first to the second year of life.
- Study 2: For this study, I analyzed the data from the same cohort, at age 2- and 4 years, to investigate gender differences in cognitive abilities, assessed by the Mullen Scales of Early Learning, and autism manifestations using the Autism Diagnostic Observation Schedule (ADOS). The analysis showed no gender differences in cognitive development or social attention difficulties at both 24- and 48 months. Indeed, cognitive and social abilities improved to a similar extent in both boys and girls over time. However, boys displayed more RRBs than girls at both 24- and 48 months.
- Study 3: To confirm the findings of Study 2, I directly observed the social attention behaviours and RRBs in 11 boys and 11 girls closely matched at 24- and 48 months of age. Again, I found no gender differences on social attention, but boys showed slightly more RRB than girls.
In conclusion, the combined results from all three studies indicate a similar developmental trajectory in young boys and girls for cognitive ability, the early signs of ASD, and for social attention difficulties. The only difference was for RRBs with boys presenting with significantly more RRBs than girls from toddlerhood to pre-school age.
As RRBs are more easily observed in the early years than social attention and communication deficits, it is possible therefore that ASD in girls can be missed considering that they display less of them. It is also possible that girls may not come to a diagnostician’s attention because the social and behavioural deficits observed in ASD may be more acceptable in girls than boys or may be more noticed in boys because of the current gender bias – that is parents and other cares of young children expect ASD to affect more boys than girls and therefore may not be so concerned about girls. It seems therefore that mis- or under diagnosis in girls may occur not because ASD symptoms are different in boys and girls, but because they are more noticeable in boys.