Scientists are still trying to establish the definitive cause(s) of autism.
There is a genetic link. In twin studies, if one twin was autistic, the other had up to a 90% chance of being diagnosed. And if one sibling was affected, a second sibling had 35 times greater risk in being diagnosed. Dr. Frazier of the Cleveland Clinic recently published research that showed that if one identical twin had autism spectrum disorder, the other twin had a 76 percent chance of also being diagnosed with it. Identical twins share the exact same genetic blueprints. The numbers are lower for fraternal twins, who have the same genetic concordance rate as do non-twin siblings. The percentage of fraternal twins who each share an ASD diagnosis is 34 percent for same-sex twins and 18 percent for boy-girl twins, Girls are less likely to be diagnosed with autism than boys. These rates are higher than for non-twin siblings—though fraternal twins share the same genetic concordance rate with regular siblings, it is theorized that because they did share the same prenatal environment, this impacted the higher rates of fraternal twins having autism than non-twin siblings.
Over the past several years, scientists have identified a number of gene mutations associated with greater risk of autism. There are currently over 100 of these so-called autism risk genes. Approximately 15% of diagnosed cases have a genetic basis that can be identified.
However, most people who have autism have no reported family history of it.
A combination of environmental factors and genetic influences is thought to be the cause: For the remaining cases, Autism is likely caused by a certain combination of environmental factors affecting particular genes in unique ways, either turning them off or on, or changing their activity levels or causing mutations. Scientists think that this combination of environmental factors and genes influences early brain development in some way, causing irregularities. Exactly what happens is not yet understood.
Although more studies are necessary, environmental factors that are believed to increase risk for autism are:
- Advanced parental age of both parents (an older dad seems to have more affect on autism outcomes than does an older mom)
- Maternal illness during pregnancy (flu, persistent fever lasting a week, use of antibiotics)
- Premature infant (less than 26 weeks)
- Infant with extremely low birth weight
- Infant that was deprived of oxygen during childbirth
- Mother exposed to pesticides or air pollution while pregnant
In a study published in the journal Pediatrics (Nov. 12, 2012) researchers at the University of Aarhus in Denmark found that a pregnant mother having the flu doubled the risk for an autistic child; a pregnant mom having a persistent fever for a week tripled the risk; and a pregnant mom using an antibiotic slightly increased the risk of an autistic child.
Many Other Causes Are Being Researched:
- Some scientists believe that abnormal levels of neurotransmitters may be involved. Neurons in the brain trigger electrical impulses, triggering the release of neurotransmitters. These are like chemical messages that then cross between synapses and ensure a variety of normal brain activities take place, including the ability for cells to produce energy. Abnormalities in this brain circuitry need further study.
- Other scientists are researching whether a pregnant woman’s overactive immune system may somehow be a factor. There is a good deal of research going on in this area. Many children with autism have gastrointestinal problems and about 70% of the body’s immune system is based in the gut. One study found that about 12% of mothers with autistic children had antibodies to fetal brain tissue.
- Still another area being looked at is abnormalities in DNA methylation. Methylation is one way in which gene expression is changed through environmental exposures. As reported in 2014 in the periodical, Molecular Psychiatry, researchers from Johns Hopkins performed studies using post-mortem brain tissues from people known to have had autism, and they found that gene expression was abnormally methylated in individuals with ASD.
- Finally, researchers are looking at a pregnant mother’s ability to manufacture glutathione, which is an important defense against toxic metals. Folinic acid (a type of folic acid) has been found to potentially reduce autism risk. Research has also shown that there may be less risk of autism if the mother took a prenatal vitamin containing folic acid prior to conception and during the pregnancy.
What Does Not Cause Autism?
As with everything about Autism, no one agrees completely on what does not cause it.
The mainstream medical community, however, has agreed on two things that do not cause autism: Poor parental practices and vaccinations. The issue of vaccinations, however, is widely questioned in parenting public health forums and autism support circles.
Poor parental practices: There is no science-based data that states that poor parenting results in an autistic child. This viewpoint first appeared in the 1940’s partly due to the lack of any science-based data on a physiological cause. Mom’s cold, distant, and rejecting personality and behavior toward a child was deemed the cause—termed the “schizophrenogenic mother.” The vast majority of the medical and scientific community has discounted this viewpoint.
Vaccinations: The Center for Disease Control and Prevention (CDC) has stated that vaccines do not cause autism. The mainstream medical community has generally backed this and has viewed the risks associated with not getting vaccinated as outweighing the risks of any currently unsupported link to autism.
Most of the concern about this issue has historically been focused on the mercury-based preservative, thimerosal. Thimerosal used to be utilized in all childhood vaccines. In 1998, thirty different vaccines containing thimerosal were routinely given to U.S. children. Public health officials at the time determined that the recommended schedule of vaccines could give some children mercury that exceeded the safe limit. In 2001 thimerosal was removed or reduced to trace amounts in all childhood vaccines except for some flu vaccines. Even with the removal of thimerosal, since 2003 the CDC funded 9 studies looking at whether there was any link between autism and thimerosal. The CDC found no link.
Today only childhood flu shots contain trace amounts of thimerosal, and thimerosal-free shots are available for those who are concerned with even the trace amounts.
Other vaccine ingredients have now come under scrutiny. Vaccines contain a variety of chemicals needed – in small amounts – to keep the vaccine potent, sterile, stable, and safe. These chemicals include preservatives (albumin, glycine), antibiotics, egg proteins, water, and more. You can request a detailed list of ingredients from your pharmacy or doctor prior to having your child vaccinated. The medical community, CDC, and other entities believe that not vaccinating your child is more dangerous to your child than the risk of vaccinations, given the serious nature of the many diseases, like polio that have been eradicated due to aggressive vaccinations in the US. There are also no studies showing that these other ingredients are linked to an increased risk of autism.
Most recently, in a 2015 study published in The Journal of the American Medical Association, researchers evaluated 95,727 children who had had the measles-mumps-rubella (MMR) vaccine and found no link between autism and vaccination. Many in the medical community state that it isn’t vaccinations that cause a seemingly healthy child to start displaying autistic symptoms, instead, autistic symptoms just typically occur during the time frame children are receiving multiple vaccinations.
Some autism-focused entities, however, such as the Autism Society, still believe that more research is warranted, in particular they would like to see more research related to the cumulative effect of multiple vaccinations that the recommendations suggest for children today. Some medical researchers in mainstream medicine view the vaccine-autism link as being one-in-a million case where there is a link (just like there may be such small links to any number of environmental factors for any given child).
There are still some in the alternative medicine and functional medical community that view vaccinations as dangerous. Most of this community believes that vaccinations are one more environmental factor that causes autism. There is a variety of research studies underway that still include the question of a vaccine-autism link, as part of environmental factors being analyzed. One such study is the Childhood Autism Risks From Genetics and the Environment (CHARGE) study that is currently being conducted at the University of California, Davis. This study has been funded by the National Institute of Environmental Health Sciences and involves more than 600 families with autism. The study is looking at genetic and environmental factors.
The CDC’s Centers for Autism and Developmental Disabilities Research and Epidemiology network (CADDRE) is also collecting environmental risk factor data, including vaccines; that might put children at risk of autism.
In the end, the concern over unvaccinated children’s health has most medical authorities supporting vaccinations. Every year, 2.5 million unvaccinated children worldwide die of diseases that vaccines could have prevented. The thought of polio, measles, whooping cough, diphtheria and other illnesses is alarming, and authorities have already seen increases in these diseases due to unvaccinated children in the U.S.