Epidemiology of autism

[7] The risk of developing autism is increased in the presence of various prenatal factors, including advanced paternal age and diabetes in the mother during pregnancy.

[5] Andrew Wakefield published a small study in 1998 in the United Kingdom suggesting a causal link between autism and the trivalent MMR vaccine.

After data included in the report was shown to be deliberately falsified, the paper was retracted, and Wakefield was struck off the medical register in the United Kingdom.

According to the new diagnostic criteria for ASD, one must have both struggles in social communication and interaction and restricted repetitive behaviors, interests and activities.

ASD diagnoses continue to be over four times more common among boys (1 in 34) than among girls (1 in 154), and they are reported in all racial, ethnic and socioeconomic groups.

Studies have been conducted in several continents (Asia, Europe and North America) that report a prevalence rate of approximately 1 to 2 percent.

[22] In autism epidemiology, point or period prevalence is more useful than incidence, as the condition starts long before it is diagnosed, bearing in mind genetic elements it is inherent from conception, and the gap between initiation and diagnosis is influenced by many factors unrelated to chance.

Research focuses mostly on whether point or period prevalence is increasing with time; cumulative incidence is sometimes used in studies of birth cohorts.

[23] Estimates of the prevalence of autism vary widely depending on diagnostic criteria, age of children screened, and geographical location.

[26] A 2006 study of nearly 57,000 British nine- and ten-year-olds reported a prevalence of 3.89 per 1,000 for autism and 11.61 per 1,000 for ASD; these higher figures could be associated with broadening diagnostic criteria.

[39] A small 2008 study found that a significant number (40%) of people diagnosed with pragmatic language impairment as children in previous decades would now be given a diagnosis as autism.

[41] A 2009 study of California data found that the reported incidence of autism rose 7- to 8-fold from the early 1990s to 2007, and that changes in diagnostic criteria, inclusion of milder cases, and earlier age of diagnosis probably explain only a 4.25-fold increase; the study did not quantify the effects of wider awareness of autism, increased funding, and expanding support options resulting in parents' greater motivation to seek services.

[42] Another 2009 California study found that the reported increases are unlikely to be explained by changes in how qualifying condition codes for autism were recorded.

[47] However, preliminary results of an epidemiological study conducted at Montreal Children's Hospital in the 200–2004 school year found a prevalence rate of 0.68% (or 1 per 147).

[48] A 2001 review of the medical research conducted by the Public Health Agency of Canada concluded that there was no link between MMR vaccine and either inflammatory bowel disease or autism.

[30] The National Health Interview Survey for 2014–2016 studied 30,502 US children and adolescents and found the weighted prevalence of ASD was 2.47% (24.7 per 1,000); 3.63% in boys and 1.25% in girls.

[57] A 2005 study of a part of Yokohama with a stable population of about 300,000 reported a cumulative incidence to age 7 years of 48 cases of ASD per 10,000 children in 1989, and 86 in 1990.

[59] A 2009 study reported that the annual incidence rate of Israeli children with a diagnosis of ASD receiving disability benefits rose from zero in 1982–1984 to 190 per million in 2004.

[68] A 2008 study in Germany found that inpatient admission rates for children with ASD increased 30% from 2000 to 2005, with the largest rise between 2000 and 2001 and a decline between 2001 and 2003.

[72] However, a perceived link between the two arising from the results of a fraudulent scientific study has caused considerable controversy, despite being subsequently disproved.

[10] Since heritability is less than 100% and symptoms vary markedly among identical twins with autism, environmental factors are most likely a significant cause as well.

[79][80] Autism is also associated with several other prenatal factors, including advanced age in either parent, and diabetes, bleeding, or use of psychiatric drugs in the mother during pregnancy.

[83] Increased chance of autism has also been linked to rapid "catch-up" growth for children born to mothers who had unhealthy weight at conception.

One study from California found a three to fourfold increased risk of autism in a small 30 by 40 km region centered on West Hollywood, Los Angeles.

[92][93] One longitudinal study had found elevated levels of perfluorodecanoic acid and zearalenone in the cord serum of children that later developed autism, suggesting that prenatal exposure may affect ASD.

[94] Key symptoms of autism spectrum disorder are impaired social and communication abilities and having a narrow scope of interest and repeated behaviors.

One scoping review has determined multiple brain structures that appear to play a role in language related symptoms in autism spectrum disorder.

For example, having a larger sized right inferior frontal gyrus is correlated with those diagnosed with autism, specifically categorized in the language impairment subgroup (but not in those without).

[95][96] Some research yields conflicting results however related to different structures and total language scores, in which a possible factor for this could be age.

[98][96] Much research centered around those with ASD that have impaired communication and seeking improvement in social interaction often investigate the use of psychosocial interventions.