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What Causes Autism?
What Causes Autism?
What causes the disorder of autism and related disorders has not been limited to a single gene, a single mutation, or a single outside environment. Even with all of the research taking places, there are still a variety of factors have the potential ability to cause autism and related disorders. Additionally, the factors might cause autism in certain people and have no effects on others. Here, we are going to explore the most prevalent potential causes of autism and similar disorders.
The Genetics Behind Autism
The Genetics Behind Autism
Important indicators that certain people can be genetically predisposed to autism are results from family and twin studies. The reason why the studies are important indicators is because identical twins share the same DNA with slight variations in how the genes can be expressed and family members share relatively the same DNA. In identical twin studies, it has been found that if one twin is affected by autism, it is a 36 to 95 percent likely that the other twin is affected. For families that have a child with ASD, the risk of having a second one with ASD increases as well [1].
The Human Genome Project and the Autisms Genome Project
The Human Genome Project and the Autisms Genome Project
In 1990, the Human Genome Project began to map the human genome. It was completed in 2003. The goal was to map the complete human genome in order to see the genetic code of a human. In 2004, the Autism Genome Project began to look through the human genome and find autism-susceptible genes. From the study, it has been found there are specific areas in the human genome that are susceptible to autism, like the 11p12-p13 on chromosome 11. Other areas of interest are chromosome 15 and region 2p16 on chromosome 2 [2].
Mutations that Increase the Risk for Developing Autism
Mutations that Increase the Risk for Developing Autism
- De novo mutations: changes in the DNA that occur spontaneously in either the parent's cell, the parent's sperm cell, or during fertilization [1].
- Copy number variants (CNVs): duplication, deletions, or rearrangements of genes and other genetic material in the DNA [2].
- Rare mutations, like ADNP, ARID1B, ASH1L, CHD2, CHD8, POGZ, SHANK3, and SYNGAP1, are linked to ASD [3].
Through various studies, it has been found that people with ASD tend to have more copies of de novo mutations than a person without the disorder. The studies then suggest that is does not depend on which gene is mutated but mutations across a variety of genes [1]. One of the important CNV deletions that has been discovered was the deletion of the a gene that codes for the neurexin protein which controls how the brain cells talk to each other. It deals with how the different cells and proteins adhere to each other. This could explain some of the symptoms and characteristics of ASD and other related disorders [2].
In total, there have been around 65 genes that have a strong relation to autism and over 200 other genes that have a weaker connection to autism. Changes in over 1,000 genes have also been related to autism and similar disorders [4].
Genetic Disorders
Genetic Disorders
It has been found out that certain genetic disorders increase a person's risk of having autism. Fragile X Syndrome, for example, is an intellectual disability that is linked to autism [1]. Retts Syndrome [2] and tuberous sclerosis [1] are two other genetic disorders that are linked to an increased risk of having autism. There are many other genetic disorders that are being investigated and have been found to increasing the likelihood of a person having autism.
Here is a video by Spectrum.org that explains why certain scientists believe that autism is a genetic condition.
Environmental Causes of Autism
Environmental Causes of Autism
The term "environmental," in this case, is used by scientists to describe what causes the disorders other than changes in the DNA of a person's genetic code. In fact, there is a possibility that up to 40 percent of the risk of having ASD is based on non-genetic factors [3].
There are prenatal risks to possibly developing ASD and there are natal risks to possibly developing ASD.
Prenatal Risks
Prenatal Risks
Prenatal risks can include the age of the parents. It has been found that the risk of autism increases 29% every ten years in for a father's age. This could be attributed to the methylation of the DNA, disorders in the sperm genomic imprinting, or the formation of de novo mutations. The mother having an older age can cause chromosome abnormalities and the need for obstetric intervention. Other prenatal risks that increase the risk for autism are being small for the gestation age, maternal bleeding during pregnancy, metabolic syndromes like diabetes, and obesity. Certain viral infections like herpes, influenza, and the chicken pox during the first trimesters increase the risk of developing autism. If the mother has Schizophrenia, anxiety, or depression, it raises the child's risk of autism almost 3 times the normal amount [5].
Natal Risks
Natal Risks
Natal risks include both a gestation age of less than 35 weeks and greater than 42 weeks cause a significant increased risk of autism in the child. Other natal risks include fetal distress, umbilical-cord complications, and cesarean delivery [5].
Vaccinations and Autism
Vaccinations and Autism
A common debate is whether vaccinations cause autism. Multiple studies have shown that vaccinations that prevent childhood infectious diseases does not increase the risk of autism [1].
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