Gender differences in parent-reported age at diagnosis of children with autism spectrum disorder
Introduction
The reported prevalence estimates of autism spectrum disorder (ASD) are always greater in males than females. The male to female ratio is around 4:1 (Baird et al., 2006; CDC, 2014; Fombonne, 2009) in the absence of intellectual impairment (see Rivet & Matson, 2011 for a review). Increased rates of ASD diagnoses in children over the last 15 years or so may be due to the broadening of, and changes to, ASD diagnostic criteria and practice, improved identification, earlier age at diagnosis in the teenage years, and different methodologies used to estimate prevalence (Russell, Collishaw, Golding, Kelly, & Ford, 2015).
Cognitively able girls may be diagnosed with ASD significantly less frequently and at an older age than boys despite there being no gender differences in the age at which parental concern is expressed (Giarelli et al., 2010). However, with the exception of learning/intellectual disability, there is little evidence to suggest what factors might be associated with earlier age at ASD diagnosis in girls. Indeed, several studies have suggested no gender difference in age at diagnosis (Mussey, Ginn, & Klinger, 2017). In a cross-cohort comparison study, Russell et al. (2015) found no gender difference in age at diagnosis nor differences in gender ratios of diagnosed children aged 7 years assessed in 1998/1999 (n = 96) and 2007/2008 (n = 209). Furthermore, in a large UK cohort study, Brett, Warnell, McConachie, and Parr (2016) found that the average age at diagnosis was 67.3 months for boys and 72.1 months for girls and had not decreased over the decade from 2004 to 2014. Although some children are now diagnosed by age 2 years, Brett and colleagues found no reduction in age at diagnosis for children diagnosed under age 3 years in the UK (Brett et al., 2016). While gender was not a significant influencing factor, earlier age at diagnosis was associated with language regression, lower socioeconomic status, greater degree of support required, greater symptom severity, and greater parental concern about initial symptoms (Brett et al., 2016; Daniels & Mandell, 2014).
There has been growing interest in the identification of ASD in girls, and it is becoming recognised that under-diagnosis or later diagnosis may be common (Dworzynski, Ronald, Bolton, & Happé, 2012; Loomes, Hull, & Mandy, 2017; Van Wijngaarden-Cremers et al., 2014). One way to measure whether there has been better detection of ASD in girls in recent years is to show whether there is evidence of change in the average age at diagnosis for girls. While Brett et al. (2016) assessed factors that influenced age at diagnosis, they did not specifically examine factors that are associated with earlier age at diagnosis independently for boys and girls. Thus, the current study builds on that of Brett et al. (2016) to examine gender differences in parent-reported age at diagnosis in large UK databases of children with ASD.
We had the following aims: First, to assess whether girls’ age at diagnosis has reduced, compared to boys’, across two age cohorts – children who were born between 1996–1999 and 2002–2005. Changes in diagnostic practices have been shown to have a substantial effect on the increased prevalence of ASD (King & Bearman, 2009). Thus, this separation of birth cohorts was chosen to better control for this potential confound of changes over a decade, so that any evidence of reduced age at diagnosis in girls is less likely to be an artefact of general changes in diagnostic practices. If ASD diagnosis in girls has become more timely, we would expect a differential reduction in age at diagnosis, for girls compared to boys, between the age periods. Second, to investigate whether age at diagnosis differed between boys and girls diagnosed across childhood. We assessed gender differences in age at diagnosis across childhood by grouping the sample at the median age at diagnosis where any differences between boys and girls would most likely be salient (see below). Finally, to examine characteristics that might be associated with earlier age at diagnosis in girls.
Section snippets
Methods
Data were available from two large representative UK databases: The Database of children with autism spectrum disorder living in the North East of England (Daslne, established in 2003; http://daslne.org) and the Autism Spectrum Database – UK (ASD–UK, established in 2011; www.asd-uk.com). Daslne covers six areas around Newcastle upon Tyne, whilst ASD-UK covers the rest of the UK. By 2017, the databases held data from over 4000 families, including information on children’s ASD and other medical
Results
Parent-reported age at diagnosis ranged from 7 to 213 months (mean = 67.0, SD = 37.2; median = 54, interquartile range = 46); only 5 parents reported an age at diagnosis below 12 months of age, therefore all parent-reported data were included. Chronological age at data collection ranged from 18 to 214 months (mean = 101.0, SD = 45.2; median = 94, interquartile range = 72). Table 1 shows descriptive statistics of chronological age and age at diagnosis of boys and girls with ASD by Year of Birth
Discussion
This large study found that, compared with boys, girls diagnosed with ASD at 5 years of age or older received their diagnosis an average of one year later. Whilst this was a small effect statistically, this difference can have a significant impact for children, families, and clinicians. This delay reduces opportunities for understanding girls’ difficulties, and accessing community support and interventions, educational support and strategies at school and for older young people, the workplace.
Declaration of conflicting interests
The authors declared that they had no conflicts of interest with respect to their authorship or the publication of this article.
Author contributions
A. Petrou analysed the data and J. R. Parr, and H. McConachie conceptualised the study and contributed to conceptual analysis. A. Petrou, J. R. Parr, and H. McConachie co-wrote the paper, and had complete access to the study data that support the publication.
Acknowledgements
We are grateful to the parents and children participating in Daslne and ASD–UK, and the child health teams who support the success of the databases through recruitment (see www.asd-uk.com for a list of participating NHS Trusts). We would also like to thank colleagues who have worked on the databases and members of the Steering Committee, Research and Parent Committees. We are grateful to the UK autism research charity, Autistica, for funding Daslne and ASD–UK (see www.autistica.org.uk).
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