Summary: Recent surveys of Autism show an increased incidence of Autism. The reasons appear to be better diagnostic criteria and tools, as well as a for greater awareness and confidence to diagnosis among health care givers. We include below some recent published worldwide reports about it. Last updated January 21, 2007

AUTISM: INCIDENCE AND SOME CAUSES

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Increased incidence of Autism: fact or artifact?

There has been a lot of advancement in the diagnostic criteria, diagnostic tools and investigations, physician awareness and the confidence among healthcare workers to diagnose Autism at an early age. This has resulted in the revision of statistical data concerning this disorder. Given below are excerpts from published data on the subject, based on Medline Search.

NEWS FLASH

US President George Bush authorized a bill in December 2006, initiated by their House of Representatives and the US Senate, to give a Research Grant of $1 Billion for research into the causes, prevention and treatment of Autism.

As one of the Representatives mentioned, the  incidence of Autism in the US this year is expected to be more than the combined incidence of new cases of AIDS + Cancer + Diabetes.


On the twin risk in autism

Hallmayer J, Glasson EJ, Bower C, Petterson B, Croen L, Grether J, Risch N.; Am J Hum Genet 2002 Oct;71(4):941-6
Autism is considered by many to be the most strongly genetically influenced multifactorial childhood psychiatric disorder. Two recent studies (Greenberg et al. 2001; Betancur et al. 2002) suggested that the twinning process itself is an important risk factor in the development of autism. Using data from our epidemiological study in Western Australia, we investigated the possibility of an increased rate of autism in twins. All children born between 1980 and 1995 with autism, Asperger syndrome, or pervasive developmental disorder not otherwise specified (PDD-NOS) were ascertained. Of the 465 children with a diagnosis, 14 were twin births (rate 30.0/1,000) compared to 9,640 children of multiple births out of a total of 386,637 births in Western Australia between 1980 and 1995 (twin rate weighted to number of children with autism or PDD per year 26.3/1,000). These data clearly do not support twinning as a substantial risk factor in the etiology of autism.

The epidemiology of autistic spectrum disorders: is the prevalence rising?

Wing L, Potter D.; Ment Retard Dev Disabil Res Rev 2002;8(3):151-61
For decades after Kanner's original paper on the subject was published in 1943, autism was generally considered to be a rare condition with a prevalence of around 2-4 per 10,000 children. Then, studies carried out in the late 1990s and the present century reported annual rises in incidence of autism in pre-school children, based on age of diagnosis, and increases in the age-specific prevalence rates in children. Prevalence rates of up to 60 per 10,000 for autism and even more for the whole autistic spectrum were reported. Reasons for these increases include changes in diagnostic criteria, development of the concept of the wide autistic spectrum, different methods used in studies, growing awareness and knowledge among parents and professional workers and the development of specialist services, as well as the possibility of a true increase in numbers.

The changing prevalence of autism in California.

Croen LA, Grether JK, Hoogstrate J, Selvin S.; J Autism Dev Disord 2002 Jun;32(3):207-15
We conducted a population-based study of eight successive California births cohorts to examine the degree to which improvements in detection and changes in diagnosis contribute to the observed increase in autism prevalence. Children born in 1987-1994 who had autism were identified from the statewide agency responsible for coordinating services for individuals with developmental disabilities. To evaluate the role of diagnostic substitution, trends in prevalence of mental retardation without autism were also investigated. A total of 5038 children with full syndrome autism were identified from 4,590,333 California births, a prevalence of 11.0 per 10,000. During the study period, prevalence increased from 5.8 to 14.9 per 10,000, for an absolute change of 9.1 per 10,000. The pattern of increase was not influenced by maternal age, race/ethnicity, education, child gender, or plurality. During the same period, the prevalence of mental retardation without autism decreased from 28.8 to 19.5 per 10,000, for an absolute change of 9.3 per 10,000. These data suggest that improvements in detection and changes in diagnosis account for the observed increase in autism; whether there has also been a true increase in incidence is not known.

Perinatal risk factors for infantile autism.

Hultman CM, Sparen P, Cnattingius S.; Epidemiology 2002 Jul;13(4):417-23
We evaluated the association of maternal, pregnancy, delivery, and infant characteristics and risk of infantile autism. We conducted a case-control study nested within a population-based cohort (all Swedish children born in 1974-1993). Cases were 408 children (321 boys and 87 girls) discharged with a main diagnosis of infantile autism from any hospital in Sweden before 10 years of age in the period 1987-1994, plus 2,040 matched controls. The risk of autism was associated with daily smoking in early pregnancy (OR = 1.4; CI = 1.1-1.8), maternal birth outside Europe and North America (OR = 3.0; CI = 1.7-5.2), cesarean delivery (OR = 1.6; CI = 1.1-2.3), being small for gestational age (SGA; OR = 2.1; CI = 1.1-3.9), a 5-minute Apgar score below 7 (OR = 3.2, CI = 1.2-8.2), and congenital malformations (OR = 1.8, CI = 1.1-3.1). No association was found between autism and head circumference, maternal diabetes, being a twin, or season of birth.

The prevalence of autistic disorder among children with a learning disability.

Deb S, Prasad KB.; Br J Psychiatry 1994 Sep;165(3):395-9
767 children with a learning disability who attended 16 different special schools in the Grampian region of north-east Scotland were studied for a diagnosis of autistic disorder according to the DSM-III-R criteria. Questionnaires were completed for 634 (82.7%) children. 14.3% of children with a learning disability fulfilled the diagnostic criteria for autistic disorder. There was a male:female ratio of 3:1. This gave a 9 per 10,000 minimum prevalence of autistic disorder among all school-age children in the Grampian region. There was a higher prevalence of autistic disorder in the cities compared with rural areas. The prevalence did not change with age but increased with decreasing IQ.

Prevalence of autism in a United States population: the Brick Township, New Jersey, investigation.

Bertrand J, Mars A, Boyle C, Bove F, Yeargin-Allsopp M, Decoufle P.; Pediatrics 2001 Nov;108(5):1155-61
This study determined the prevalence of autism for a defined community, Brick Township, New Jersey, using current diagnostic and epidemiologic methods. The target population was children who were 3 to 10 years of age in 1998, who were residents of Brick Township at any point during that year, and who had an autism spectrum disorder. Autism spectrum disorder was defined as autistic disorder, pervasive developmental disorder-not otherwise specified (PDD-NOS), and Asperger disorder. The prevalence of all autism spectrum disorders combined was 6.7 cases per 1000 children. The prevalence for children whose condition met full diagnostic criteria for autistic disorder was 4.0 cases per 1000 children, and the prevalence for PDD-NOS and Asperger disorder was 2.7 cases per 1000 children.

Autism in Northern Finland.

Kielinen M, Linna SL, Moilanen I.; Eur Child Adolesc Psychiatry 2000 Sep;9(3):162-7
The diagnostic criteria and the methods of ascertainment influence the prevalence. The age specific incidence obtained in this study showed the cumulative incidence to be lowest, 6.1 per 10,000, in the oldest age group of 15- to 18-year-old children, and highest, 20.7 per 10,000, in the age group of 5-7 year-olds, when the criteria of the ICD-10 and the DSM-IV were used.

Cumulative incidence and prevalence of childhood autism in children in Japan

Honda H, Shimizu Y, Misumi K, Niimi M, Ohashi Y.; Br J Psychiatry 1996;169(2):228-35
An epidemiological survey of childhood autism as defined in ICD-10 Research Criteria was conducted in the northern part of Yokohama, Japan. Cumulative incidence and prevalence were 16.2 per 10,000 and 21.1 per 10,000, respectively.

Autism: not an extremely rare disorder

Gillberg C, Wing L.; Acta Psychiatr Scand 1999 Jun;99(6):399-406
Aim: To study autism over time in order to ascertain whether there has been an increase in its prevalence in recent years. The early studies yielded prevalence rates of under 0.5 in 1000 children, whereas the later ones showed a mean rate of about 1 in 1000. There was a marked difference in prevalence rates between those studies that included some children born before 1970 (low rates) and those that included only children born in 1970 and after (high rates). This is probably due to the lower rates obtained by use of criteria strictly based on Kanner's description of his syndrome. The US studies reported atypically low rates. There was a highly significant estimated increase with calendar year in the non-US studies (3.8% per year).

[Infantile autism among children in the county of Nordland. Prevalence and etiology];

Herder GA.; Tidsskr Nor Laegeforen 1993 Aug 10;113(18):2247-9
Few epidemiological studies of infantile autism have been conducted in Norway. A prevalence of four per 10,000 children was found in Nord-Trondelag. Studies from Sweden, England and Japan show prevalence figures of 2-13 per 10,000. The aim of this study was to establish the prevalence of infantile autism in Nordland county and look for causal factors and disabilities among the children. Together with the Autism-Team we found 28 persons, born between 1975 and 1991, who lived in the county in 1992. This gives a prevalence of 5.5 per 10,000. 21 were boys, seven girls, 26 were mentally retarded, 13 had no verbal speech. Nine had epilepsy. 13 children were diagnosed before the age of four.

Changes in the incidence of childhood autism and other autistic spectrum disorders in preschool children from two areas of the West Midlands, UK

Powell JE, Edwards A, Edwards M, Pandit BS, Sungum-Paliwal SR, Whitehouse W.; Dev Med Child Neurol 2000 Sep;42(9):624-8
The incidence of childhood autism and other autistic spectrum disorders (ASDs) in preschool children was determined for two areas of the West Midlands between 1991 and 1996. The incidence rate per 10,000 children per year for the combined areas was 8.3 for all children with ASDs, 3.5 for classical childhood autism (CA), and 4.8 for other ASDs. While rates for classical CA increased by 18% per year, a much larger increase (55% per year) was seen for 'other ASDs', suggesting that clinicians are becoming increasingly able and/or willing to diagnose ASDs in preschool children.

The epidemiological study of autism in Fukushima-ken.

Hoshino Y, Kumashiro H, Yashima Y, Tachibana R, Watanabe M.; Folia Psychiatr Neurol Jpn 1982;36(2):115-24
A survey of children aged under 18 years in Fukushima-ken (prefecture) in Japan showed that 2.33 per 10,000 children suffered from early infantile autism. The average of prevalence rates of autistic children born between 1968 and 1974 was 4.96 per 10,000 children. Autistic boys outnumbered autistic girls with a sex ratio of 9 : 1.

As is evident, the incidence of Autism varies from one country / state / county to another, depending on the diagnostic acumen and facilities available. However, the fact remains that autistic tendencies are much more common than suspected. Earlier diagnosis may give the child a better long term prognosis.


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