Epidemiology of Autism Spectrum Disorders

doi:10.1016/j.pcl.2011.10.003

Pediatric Clinics of North America

Volume 59, Issue 1, February 2012, Pages 27-43

https://doi.org/10.1016/j.pcl.2011.10.003 Get rights and content

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Incidence

In a retrospective review of health and education records in 2006 from participating sites in the Autism and Developmental Disabilities Monitoring (ADDM) network, the incidence of ASD is 1 child in every 110 children.² This finding is similar to the estimates that 1 in 91 children aged 3 to 17 years in the United States will be diagnosed with ASD based on data from the 2007 National Survey of Children’s Health.³ These numbers are similar to regional data whereby, in a study of birth cohorts in

Prevalence of autism in the United States

Epidemiologic data gathered over the last 40 years report that the conservative estimate of ASD prevalence is 27.5 per 10,000 individuals; however, the prevalence estimate based on newer surveys is 60.0 per 10,000 individuals.⁵ A review of 23 published articles reporting the prevalence of ASD found that the pooled estimate was 20.0 per 10,000 individuals, although there was a large variation among the analyzed studies as reflected by the 95% confidence interval of 4.9 to 82.1.⁶ However, the

Prevalence of autism globally

The prevalence of typical autism across the world is generally reported to be 10 per 10,000.⁵ When analyzing the prevalence of typical autism, the pooled prevalence of published reports from 37 studies was 7.1 per 10,000; however, again, there were large variations with a wide 95% confidence interval of 1.6 to 30.6.⁶ Another systematic review of 32 surveys that were published from 1966 to 2001 reporting the prevalence of typical autism found that the range of prevalence estimates of AD to be

Prevalence of autism in Asia

The prevalence of ASD is similar in Asia. A Taiwanese 2005 national database review revealed a cumulative prevalence of ASD to be 28.72 per 10,000 individuals.¹³ This finding is a dramatic increase from the Taiwanese prevalence of 1.71 per 10,000 individuals that was reported in 1996.¹³ In Japan, the prevalence of ASD is reported to be 27.2 per 10,000 individuals.¹⁴ In Chinese children younger than 15 years of age, the prevalence of ASD as estimated from a government registry from 1986 to 2005

Prevalence of autism in Europe

The prevalence of ASD in Europe tends to be similar to the reported prevalence estimates in the United States and in Asia. A stratified, multiphase, random sample survey of adults living in England determined a prevalence of ASD of 98 per 10,000 individuals.¹⁸ A diagnosis survey distributed to children aged 5 to 9 years who were on the Special Educational Needs register in the United Kingdom determined the prevalence of ASD to be 94 per 10,000 and the prevalence of autism to be 11 per 10,000.¹⁹

Change in prevalence since 1940

Most studies conducted between 1960 and 1980 reported the prevalence of ASD to be 2 to 5 per 10,000, whereas studies published in early 2000 reported prevalences ranging from 30 to 60 per 10,000 individuals.³ This rate is still approximately half the rate that recent US studies have reported, as previously discussed. The US Department of Developmental Services reported that, between 1991 and 1997, there was a 556% increase in the prevalence of childhood autism.²⁵ From 1997 to 2008 the rate of

Conditions associated with autism

Although the cause of autism and ASD has not been elucidated, it is widely accepted to be a disorder of brain development. Therefore, it stands to reason that psychiatric conditions are a common comorbidity. In a large national survey, 87.3% of children aged 6 to 17 years diagnosed with ASD also had attention-deficit disorder or attention-deficit/hyperactivity disorder (ADHD), anxiety problems, behavioral or conduct problems, depression, or developmental delay. Among these conditions, the most

Risk factors for autism

There are numerous risk factors for autism that have been postulated. The following discussion is meant to discuss some of the more commonly proposed risk factors with scientific evidence to support this claim but is not inclusive of all postulated risk factors.

Anatomic traits with autism

Beginning with Kanner’s original description of autism, which described an increased rate of macrocephaly, researchers continue to study anatomic traits that may be associated with autism. Dysmorphic features and minor physical anomalies are more common in individuals with autism than in the general population.68, 74 In a study using a Waldrop scale to detect the presence or absence of 41 different minor physical anomalies in children with a mean age of 7 years, 96% (n = 23) had significantly

Genetic syndromes associated with autism

Features of autism have been reported in several genetic syndromes, which are listed in Table 1.75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91

Prognosis

The prognosis of autism reported in the literature varies with autism severity and comorbidities. However, overall, children with autism are reported to have a poorer health status.⁹⁴ In very young children with autism, there is a strong association between autism severity and impaired cognitive function. Specifically, children with an IQ less than 70 have more social, play, and stereotyped behavior deficits than children with a borderline or normal IQ. In contrast, there is no significant

Morbidities

There are significant morbidities associated with autism and ASD. Earlier, the prevalence of psychiatric symptoms in parents of individuals with autism was discussed; however, those with autism and ASD may also suffer from psychiatric symptoms. The mean score for the Global Assessment of Functioning (GAF) scale for a group of individuals with autism who were selected from 3 population-based studies was reported to be 21.1.⁹⁷ This GAF score is classified as serious impairment or inability to

Mortalities

There is excess mortality in autism, especially when comorbid with epilepsy.¹⁰⁴ Based on data from the California Developmental Disability System from 1998 to 2002, the mortality for individuals with autism was significantly higher than that of the general population.¹⁰⁵ A Swedish study of individuals with autism found the mortality rate to be 5.6 times higher than expected.⁹⁷ A Danish study reported the risk of dying in individuals with autism was nearly twice that of the general population,

Summary

Autism is a life-altering diagnosis for patients, their family, and the community. As autism becomes increasingly prevalent, knowledge of ASDs is crucial for health professionals. There is ongoing debate within the literature about the cause of the increased prevalence; however, regardless of cause, physicians need to be aware of the medical implications a diagnosis of autism or ASD has. This review covers incidence, prevalence, associations, comorbidities, and mortality of ASD; however,

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