From the Guidelines
The rising prevalence of Autism Spectrum Disorder (ASD) is likely caused by a combination of genetic and environmental factors, with environmental factors playing a significant role in the dramatic increase in prevalence over the past few decades 1.
Key Factors Contributing to the Rising Prevalence of ASD
- Genetic factors: While genetics are an important risk factor, they would not account for the dramatic rise in prevalence during this span of time, nor do changes in diagnostic criteria 1.
- Environmental factors: Growing evidence suggests that environmental factors and gene–environment interactions contribute to the etiology of the disorder, with some autism-related genes being targeted by environmental pollutants such as pesticides, heavy metals, bisphenol A (BPA), and phthalates 1.
- Early developmental period: The prenatal period is a sensitive time when the developing brain is particularly susceptible to disruptions from environmental chemicals, and subtle signs of autism can be detected as early as 9 months 1.
- Endocrine disruptors: The role and potential mechanisms of environmental endocrine disruptors in the etiology of autism have been discussed, with studies suggesting that a decreased second digit-to-fourth digit ratio, indicating increased fetal testosterone exposure, is associated with an autism spectrum disorder diagnosis 1.
Importance of Further Research
Further research is needed to fully understand the causes of the rising prevalence of ASD, including the investigation of environmental chemical exposures during early life stages and their potential impact on the developing brain 1.
Clinical Implications
Genetic testing, including chromosomal microarray analysis, is warranted and clinically indicated for all suspected cases of ASD, and may help identify specific genetic syndromes and inform prognosis and treatment targets 1.
From the Research
Possible Causes of Rising Prevalence of Autism Spectrum Disorder (ASD)
- Changes in diagnostic criteria: Studies have shown that changes in diagnostic criteria, such as the broadening of the diagnostic concept over time, may account for some of the apparent increase in prevalence 2, 3, 4.
- Increased awareness and recognition: Growing awareness and knowledge among parents and professional workers, as well as the development of specialist services, may also contribute to the rising prevalence of ASD 2, 5, 6.
- Changes in reporting practices: Changes in reporting practices, such as the inclusion of outpatient contacts, can also explain some of the increase in reported ASD prevalence 3.
- Genetic factors: There is strong evidence that complex genetic factors play a major role in the etiology of ASD, and family studies point to a strong hereditary component in the aetiology of autism 2, 6.
- Environmental factors: While some environmental risk factors, such as vaccines, mercury, and heavy metal exposure, have been suggested as possible causes of ASD, there is no conclusive evidence to support these claims, and the gene-environment interplay has not received enough attention in scientific research 6.
Factors Contributing to the Apparent Increase in Prevalence
- Methodological differences across studies: Different methods used in studies can also contribute to the apparent increase in prevalence 5, 4.
- Broadening of the diagnostic concept: The broadening of the diagnostic concept over time may also account for some of the apparent increase in prevalence 2, 4.
- Increased public awareness: Higher public awareness of ASD has generated several controversial theories of causation, and may also contribute to the rising prevalence of ASD 6.