Prevalence of autism spectrum disorders in an Icelandic birth cohort.
A steady increase in the prevalence of autism spectrum disorders (ASD) has been reported in studies based on different methods, requiring adjustment for participation and missing data.
Recent studies with high ASD prevalence rates rarely report on co-occurring medical conditions.
The aim of the study was to describe the prevalence of clinically confirmed cases of ASD in Iceland and concomitant medical conditions.
The cohort is based on a nationwide database on ASD among children born during 1994-1998.
A total of 267 children were diagnosed with ASD, 197 boys and 70 girls. Only clinically confirmed cases were included. All received physical and neurological examination, standardised diagnostic workup for ASD, as well as cognitive testing. ASD diagnosis was established by interdisciplinary teams. Information on medical conditions and chromosomal testing was obtained by record linkage with hospital registers.
Two tertiary institutions in Iceland. The population registry recorded 22 229 children in the birth cohort.
Prevalence of all ASD was 120.1/10 000 (95% CI 106.6 to 135.3),
for boys 172.4/10 000 (95% CI 150.1 to 198.0) 1.72 per 100
and for girls 64.8/10 000 (95% CI 51.3 to 81.8). .648 per 100
Prevalence of all medical conditions was 17.2% (95% CI 13.2 to 22.2), including epilepsy of 7.1% (95% CI 4.6 to 10.8).
The proportion of ASD cases with cognitive impairment (intellectual quotient <70) was 45.3%, but only 34.1% were diagnosed with intellectual disability (ID).
Children diagnosed earlier or later did not differ on mean total score on a standardised interview for autism.
The number of clinically verified cases is larger than in previous studies, yielding a prevalence of ASD on a similar level as found in recent non-clinical studies. The prevalence of co-occurring medical conditions was high, considering the low proportion of ASD cases that also had ID. Earlier detection is clearly desirable in order to provide counselling and treatment.
Further Readings of Interest
Autism in the Faroe Islands: an epidemiological study.
The Faroe Islands are considered to be a genetic isolate. This population study of the prevalence of autism sought to identify a representative cohort for future genetic studies.
In 2002 all schools were screened for autism spectrum disorders. The target population were all children born in 1985 through 1994 and living in the Faroe Islands on December 31, 2002.
Children who screened positive for autism characteristics were examined using the Diagnostic Interview for Social and Communication Disorders (DISCO).
Of the children aged 8 through 17 years, 0.56% had childhood autism, Asperger syndrome or atypical autism. .56 per 100
The male:female ratio was just under 6:1. The prevalence of autism in the Faroe Islands was very similar to that reported from many western countries.