This is exactly the same sex ratio as has been reported for children with ASD who have severe to profound learning disabilities (Fombonne, 2003). The provisional sex ratio of those boys and girls at very high risk of ASD was found to be 2:1. Unlike most trait measures, our screening questionnaire of social communication competence was not developed from a male ASD prototype, but from a female prototype (Skuse et al, 2005). One approach we have taken is to evaluate ASD traits by screening a general population sample of typical children, ascertained in the course of a UK birth cohort study (ALSPAC study team, 2001). Clinical experience of interviewing many ‘high-functioning’ females with ASD in the UK confirms a widespread ‘wish to act normal’ which is not so prevalent among affected males at any age.Īs we lack a biomarker for ASD, the opportunities to validate the hypothesis that there is a large number of undiagnosed females with ASD seem limited. These include, first, a biologically engendered greater awareness of other females’ social behaviour, plausibly related to the possession of a second X-chromosome (Skuse, 2000) and, second, the influence of socialization pressures that have evolved in concert with those biological differences (Adler et al, 1992). The motivation for compensation comes both from influences that are common to all females. If there are girls out there in the general population with these characteristics, who have not been diagnosed, how would we recognise them? If there really is an ascertainment bias, one possibility is that those females with higher IQ, especially verbal IQ, are able to disguise their symptoms – a process that is known as ‘compensation’ (Lai et al, 2011). The DSM-5 defines two dimensions of impairment associated with an ASD, comprising social communication deficits, and repetitive/stereotyped interests and behaviors, with sensory sensitivities. Second, there is a persisting tendency to recognise autism in girls only if it is associated with generalized developmental delay. First, ASD is still disproportionately recognised in boys girls in adolescence are rarely newly diagnosed (at least, in the USA). Reassignment impacted primarily on girls, where prevalence jumped over 60% from the 2011-2012 figure (compared with a mere 2% increase in boys), and the findings have two significant implications. That change led many children who had previously been categorized as having primary generalized developmental delay to be reassigned to an ASD category. In 2014, there was a change in the way the telephone survey was conducted. By 2012 about 1 in 30 boys in the USA had been given a diagnosis of an ASD, compared with just 1 in 140 girls. This increase in ascertainment has been predominantly of boys. They also reveal that by far the greatest change has been among children in mid to late adolescence, the great majority of whom do not have severe to profound learning disabilities. The figures show the expected rapid increase. This survey reflected diagnoses that were provided to families by paediatricians from around the United States. Recent epidemiological evidence from the National Center for Health Statistics reports changes in the apparent prevalence of autism spectrum disorders in school age over the period from 2007 to 2014 (Blumberg et al, 2013 Zablotsky et al, 2015). Leading clinical centres in the USA have almost never diagnosed ‘high functioning females’, so in North America there is a dearth of research on girls and women with autistic traits whose verbal IQ is above average. The male:female ratio is widely found to be 4:1 in ascertained cases, a figure that disguises the remarkable fact that among those with very low IQ the ratio is only 2:1. A high proportion were reported to have associated neurological complications such as early developmental regression and/or epilepsy. For many years, diagnosticians regarded the typical child with autism as male with generalized learning difficulties. As diagnostic criteria developed, and standardized instruments were devised to measure autistic traits, Kanner’s male-typical template – associated with severe to profound learning disability – was used for validation. It is less well-known that he conducted a follow-up study in 1971, and discovered that all those girls were in State Hospitals, virtually uncommunicative to both staff and their families (Kanner, 1971). Three of these 11 were girls, and as children their symptomatic profiles were very similar to those of the boys. He described 11 children with what would now be regarded as severe autism. The concept of an autistic disorder is generally accepted to have originated with Leo Kanner and his classic 1943 account of ‘Autistic Disorders of Affective Contact’ (Kanner, 1943).
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