Autism Increase Not Due to Better Diagnosis

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Autism Increase Not Due to Better Diagnosishttp://www.niehs. nih.gov/news/ newsletter/ 2009/april/ extramural- papers.cfm# Autism A study conducted by NIEHS-funded researchers at the University of California Davis found that the seven- to eight-fold increase since 1990 in the number of children born in California and later diagnosed with autism cannot be explained by changes in how the condition is diagnosed or counted. The researchers also conclude that the trend is not slowing and suggest that the research focus should shift from genetics to the multitude of chemical and infectious agents in the environment that could be involved in the rapid rise in the incidence of autism.The results of the investigation show that the incidence of autism by age six in California

increased from fewer than 9 cases per 10,000 children born in 1990 to more than 44 per 10,000 children born in 2000. Migration patterns and changes in diagnosis were ruled out as possible reasons for the increase. The results show that less than one-tenth of the increase can be attributed to the inclusion of milder cases of autism.These researchers are currently involved in two large studies aimed at discovering possible environmental factors and gene-environment interactions responsible for autism. They are focusing on the potential effects of metals, pesticides and infectious agents on neurodevelopment.

 

Epidemiology. 2009 Jan;20(1):84- 90.

The rise in autism and the role of age at diagnosis.http://www.ncbi. nlm.nih.gov/ pubmed/19234401

Hertz-Picciotto I, Delwiche L.

Department of Public Health Sciences, University of California, Davis, California 95616, USA. ihp (AT) ucdavis (DOT) edu

BACKGROUND: Autism prevalence in California, based on individuals eligible for state-funded services, rose throughout the 1990s. The extent to which this trend is explained by changes in age at diagnosis or inclusion of milder cases has not been previously evaluated.

 

METHODS: Autism cases were identified from 1990 through 2006 in databases of the California Department of Developmental Services, which coordinates services for individuals with specific developmental disorders. The main outcomes were population incident cases younger than age 10 years for each quarter, cumulative incidence by age and birth year, age-specific incidence rates stratified by birth year, and proportions of diagnoses by age across birth years.

 

RESULTS: Autism incidence in children rose throughout the period. Cumulative incidence to 5 years of age per 10,000 births rose consistently from 6.2 for 1990 births to 42.5 for 2001 births. Age-specific incidence rates increased most steeply for 2- and 3-year olds. The proportion diagnosed by age 5 years increased only slightly, from 54% for 1990 births to 61% for 1996 births. Changing age at diagnosis can explain a 12% increase, and inclusion of milder cases, a 56% increase.

 

CONCLUSIONS: Autism incidence in California shows no sign yet of plateauing. Younger ages at diagnosis, differential migration, changes in diagnostic criteria, and inclusion of milder cases do not fully explain the observed increases. Other artifacts have yet to be quantified, and as a result, the extent to which the continued rise represents a true increase in the occurrence of autism remains unclear.

PMID: 19234401 [PubMed - in process]

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