From electromagnetic waves to air pollution, there are dozens of possible causes of autism. Researchers have been working for decades to find out what is responsible for the growing number of children diagnosed with this developmental disorder.
35 Possible Causes of Autism
Over the years, researchers have focused on whether autism is a genetic disorder or if it is caused by environmental factors. Many theories point to a combination of genetic and environmental causes or to chemical imbalances within the body. In most cases, scientists need to conduct more research to determine if the theory is legitimate.
Possible Genetic Causes
- CYP27B1 gene mutation - Studies, such as one published in Cellular and Molecular Neurobiology in 2010, suggest that a genetic mutation in the CYP27B1 gene may lead to an inability to process Vitamin D and may play a role in the development of autism.
- De novo gene mutations - Errors during the copying of DNA, called de novo mutations, may be responsible for some cases of autism, according to a 2007 study published in the journal Science. The study found that many individuals with autism had these genetic mutations, and these results have been corroborated by many subsequent studies.
- Fragile X syndrome - Although it isn't the cause of all cases, fragile X syndrome is the basis for some forms of autism.
- NLGN4 gene deletion - In 2008, the European Journal of Human Genetics published an article asserting that the deletion of a certain gene on the X-chromosome may cause some cases of autism and that some people may carry this deletion with mild or no symptoms.
- Oxytocin receptor mutation - A commentary in the journal BMC Medicine, published in 2010, asserts that many of the genetic mutations that may be associated with autism affect the reception of the bonding hormone oxytocin.
- X-chromosome mutations - A 2010 study in the journal Molecular Psychiatry found that people with ASD or schizophrenia were more likely to have mutations on the X-chromosome, possibly accounting for the greater number of males affected by both disorders.
Possible Environmental Causes
- Advanced parental age - Studies, such as one published in the American Journal of Epidemiology in 2008, have found that children born to older parents were more likely to have autism.
- Air pollution - Several studies have examined the role of air pollution in autism. In 2013, the journal JAMA Psychiatry published a study that found a strong correlation between autism and air pollution related to traffic.
- Artificial sweeteners - Some people believe that the use of artificial sweeteners and autism are related, although this theory has not been proven with research.
- Brain injury - Some studies have also focused on whether brain injury can cause autism. Researchers focused on injuries during fetal development, as well as those after birth.
- Electromagnetic radiation - An idea put forward in the journal Medical Hypotheses in 2004 suggests that exposure to radiofrequency electromagnetic radiation in utero or early in development could cause autism.
- Fertility drugs - A few studies have focused on fertility drugs and autism, exploring whether exposure to these drugs may make it more likely for a baby to develop ASD.
- Fever-suppressing medications - One hypothesis, which was published in BMC Pediatrics in 2003, asserts that fever-suppressing medications like ibuprofen could be one cause of autism. This has not been proven.
- Flavonoid deficiency - Recent studies, such as one published in 2009 in the Journal of Neuroimmunology, examine whether an expectant mother who consumed flavonoids, chemicals found in many fruits, could expect protection for her baby against autism.
- Folic acid - An important study published in the Journal of the American Medical Association in 2013 found that folic acid deficiency during pregnancy could be a cause of autism.
- Heavy metals - Some studies, such as one published in the journal Medical Hypotheses in 2010, assert that prenatal exposure to heavy metals like cadmium, nickel, and mercury may cause genetic mutations that result in autism.
- Lyme disease - The Lyme Induced Autism Foundation seeks to raise awareness for the theory that autism could be caused by infections like Lyme disease.
- Maternal infection - Several studies, such as this 2010 one published in the Journal of Autism and Developmental Disorders, have found a relationship between a severe maternal infection during pregnancy and a later diagnosis of autism.
- Medications during pregnancy - Certain medications that the mother takes during pregnancy may result in children receiving a diagnosis of autism. Several studies, including this one from 2002 in Pediatric Research, focus on thalidomide and valproic acid.
- Prenatal vitamins - One study published in Epidemiology in 2012 found that the mothers of children with autism were less likely to have taken prenatal vitamins during the first three months of their pregnancy.
- Television - The National Bureau of Economic Research suggests the possibility that autism may be caused by too much television time, since the increase in autism diagnoses corresponds with the increased number of households with cable TV.
- Terbutaline - Early studies examined suggested there was a link between the asthma and pre-term labor drug terbutaline and autism rates, but more recent research sheds doubt on this theory.
- Thimerosal - The vaccine preservative thimerosal has long been a suspected environmental factor, but most research has refuted the idea that thimerosal exposure can cause autism.
- Thrush - Some alternative medicine practitioners believe that an overgrowth of yeast can lead to autism. Studies have not demonstrated a conclusive link between thrush and ASD.
- Vaccines - There are conflicting views on whether vaccines may cause autism, although the majority of research studies have found that there is no link.
- Vitamin D deficiency - A 2008 article in Medical Hypotheses suggested that vitamin D deficiency during pregnancy and early development might be one of the causes of autism. Several studies have focused on this issue, but the results are inconclusive.
Other Possible Causes
- Adrenal fatigue - Some people believe there may be a link between the adrenal fatigue syndrome (which is not recognized by the medical community) and autism. Studies have not supported this theory.
- Autoimmune diseases - Researchers have studied whether a family history of autoimmune diseases like asthma, type 1 diabetes, and rheumatoid arthritis may cause autism. Studies have shown that these and other autoimmune diseases are more common in families with ASD.
- Celiac disease - Some scientists have conducted research to determine whether there is a causal link between celiac disease and autism, but results are conflicting.
- Epigenetic factors - Many researchers believe that autism may be caused by epigenetic factors, environmental influences that cause certain genes to be expressed. A review of the literature published in Human Molecular Genetics in 2006 indicates this is a promising research area.
- Gestational diabetes - Many studies have examined the role of gestational diabetes in contributing to autism. A 2012 study published in Pediatrics showed that a diagnosis of gestational diabetes increased the risk of ASD.
- Gut microbia - A 2012 article in the journal Digestive Diseases and Sciences suggests that an imbalance of bacteria in the intestines could result in autism.
- Immune system - Several studies, including one from 2008 published in the journal Behavioral Brain Research, have found that the immune system is disregulated in people with autism. Tests of brain and spinal fluid from individuals with ASD show that the immune system was activated.
- Mirror neuron dysfunction - Mirror neurons are partially responsible for the brain's ability to interact with others, and there are several studies examining mirror neurons as the cause of autism. Results are inconclusive.
- Poor neonatal health - General health complications in newborn babies can cause them to be vulnerable to autism, according to a 2011 article in Pediatrics.
Correlation or Causality
When considering autism research, it's very important to remember the distinction between correlations and causes. A correlation means that two factors occur at the same time, but it doesn't indicate that one factor causes the other. Although many studies seek to draw a conclusion about the cause of autism, they actually show only a correlation.
It's easy to get confused as you read this type of research, but you can clear things up for yourself by asking whether the research actually shows that something caused ASD.
Dozens of Explanations
There are dozens of possible explanations for ASD, ranging from environmental triggers to co-existing health conditions or genetic mutations. Researchers are working all the time to find an explanation for this perplexing condition.