Epidemiology

There are estimated to be around 52 million people living with ASD worldwide.[18] The detected prevalence of ASD has increased substantially throughout the world, although since 2012, prevalence in the US may have plateaued.[7][19]​​​[20][21][22][23][24]​​ Data suggest that the rise in ASD diagnosis has been accompanied by a fall in the prevalence of other neurodevelopmental disorders and that more accurate clinical diagnosis underlies the increase in detected prevalence.[25][26]​​ Other data suggest that at least 1% of children have ASD; some studies report a prevalence of around 1% to 2% in the US and other industrialised countries.[22][27]​​​ One report from the US Centers for Disease Control estimated that 1 in 44 children aged 8 years has ASD, and that ASD was 4.2 times more prevalent in boys than girls.[10]

Within the US, there is some evidence to suggest that Hispanic and African-American children are relatively under-diagnosed compared with white, non-Hispanic children, especially those with average to above average intelligence.[28] In the US, earlier diagnosis is typically seen in children of higher socioeconomic status and with better access to services.[29] Lower rates of ASD are reported in resource-limited settings, which is likely, in part, to reflect difficulties in collecting epidemiological data.[30]

It is estimated that between 40% to 80% of children with ASD have an intellectual disability. Specific learning disorders or disabilities, such as dyslexia or dyscalculia, may also occur in ASD.[6][10] People with ASD may also have other neurodevelopmental disorders; co-occurring ADHD is common.[31]​​[15][16][17] Coexisting mental health problems, such as depression, anxiety, and sleeping difficulties, are also more common in people with ASD than in their age-matched peers; anxiety disorders are experienced by around 50% of children and adults, depression by around 10% of children and 25% to 50% of adults, and sleeping difficulties by around 50% to 80% of children.[32][33][34][35][36][37][38][39] There is some evidence to suggest that older adults with ASD experience a reduction in their risk of psychiatric comorbidities compared with in their youth, and in particular in their risk of social phobia.[37]

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