From the Guidelines
The rise in autism spectrum disorder (ASD) prevalence is most credibly explained by a combination of genetic, environmental, and improved diagnostic factors, rather than a single cause. The diagnostic criteria for ASD have broadened significantly since the 1980s, now encompassing a wider spectrum of behaviors and including milder cases that previously went undiagnosed 1. Healthcare providers, educators, and parents have become more knowledgeable about recognizing autism symptoms, leading to earlier and more frequent identification. Standardized screening tools are now routinely used during well-child visits, catching cases that would have been missed in previous decades. While genetic factors play a significant role in autism risk, with hundreds of genes identified as contributors, environmental factors may also play a role, including advanced parental age, certain prenatal exposures, and premature birth 1. Importantly, extensive research has conclusively debunked any link between vaccines and autism. Some key environmental factors that have been associated with an increased risk of ASD include exposure to pesticides, heavy metals, bisphenol A (BPA), and phthalates 1. Additionally, certain genetic mutations associated with ASD may also confer high risk of comorbidities, including epilepsy, motor impairment, and sleep disturbance 1. The apparent "epidemic" of autism likely represents our improved ability to recognize and diagnose the condition, as well as some true increase due to identified risk factors, rather than an actual increase in its occurrence. Key points to consider include:
- Genetic factors contribute to ASD risk, but do not account for the dramatic rise in prevalence over the past few decades 1
- Environmental factors, such as exposure to certain chemicals, may play a role in ASD development 1
- Improved diagnostic criteria and screening practices have led to increased detection of ASD cases 1
- The role of the clinical geneticist is to determine the etiology of ASD, if possible, and to provide counseling for the family 1
From the Research
Environmental Factors
- Maternal exposure to certain substances, such as valproic acid, acetaminophen, and heavy metals like cadmium, lead, arsenic, and mercury, has been linked to an increased risk of autism spectrum disorder (ASD) 2, 3.
- Other environmental factors, including maternal infection, folic acid supplementation, and electromagnetic radiation, have also been considered as potential contributors to the rise in ASD 4.
- The role of environmental factors in the development of ASD is complex and may involve interactions with genetic susceptibilities 5.
Genetic Factors
- Genetic polymorphisms, such as those affecting cytochrome P450 enzymes, have been associated with an increased risk of ASD 4.
- Hundreds of potential genes have been identified as contributing to the risk of ASD, with many overlapping between ASD, schizophrenia, depression, and cardiometabolic disorders 3.
- Genetic factors may underlie the differential vulnerability to environmental risk factors of susceptible individuals 5.
Diagnostic and Awareness Factors
- Changes in diagnostic criteria and increasing awareness and recognition of ASD have contributed to the reported rise in incidence and prevalence 6.
- Broadening of the diagnostic concept and increased screening, including of adults and girl children, have also played a role in the increased prevalence of ASD 3.
Other Factors
- Maternally derived antibodies, maternal infection, and measles, mumps, rubella vaccination have been considered as potential contributors to the rise in ASD, although the evidence is not conclusive 4, 6.
- Epigenetic factors, including impaired methylation and mutations of mecp2, have been associated with ASD and related disorders 4.