According to the National Institute Of Health, scientists don’t know what is the exact autism cause. From the time when autism spectrum disorder (ASD) was first discovered, in the 1940s, very little was known until the last few decades of our existence.
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As given in the Centers for Disease Control and Prevention (CDC) report released on April 2018 based on the reports of 2014 medical records, there is a 15 percent increase in autism prevalence nationally.
The new estimate say that, 1 in 58 kids ( 1 in 151 girls and 1 in 37 boys) have autism spectrum disorder (ASD) compared to the previous years’ data of 1 in 69 children.
For most of the people, autism is a lifelong condition with its still unclear causes, which means there is an unacceptable gap in our awareness especially in the areas of social inclusion, employment, and housing. Every year, approximately 50,000 children with autism, unfortunately, age out of school-based services.
It becomes not only important but extremely essential to increase autism awareness everywhere around the world. Autism is very complex and two people with autism can be different from each other as there are many possible causes of autism. Although, when it comes to understanding the theory of causation of autism, you will not get the exact cause of autism. Scientists are still studying what causes autism?
Causes of Autism
The causes of Autism has a strong Genetic basis along with Heritability of Autism, Birth defects, and Childhood Immunization. Once the MMR vaccination was also linked with the causes of Autism but due to the lack of supporting evidence this theory was denied.
Autism has distinct causes which often co-occur but the genetics of Autism is most common and is complex as it is unclear what the causes of ASD is either more related to rare mutation or by the rare multigene interaction of common genetic variants. The complexity of the genetics of autism arises because of the interaction among multiple genes, environment, and epigenetic factors. These interactions are inheritable and affect the gene expression but do not change the DNA sequencing.
The genetic factor is predominate to cause Autism. However, the autism does not have a single cause but it is a complex disorder with a set of core aspects that have distinct causes. The environmental factors contributing to the causes of Autism are certain foods, infectious diseases, heavy metals, solvents, diesel exhaust, PCBs, phthalates, and phenols which are used with plastic products, pesticides, brominated flame retardants, alcohol, smoking, illicit drugs, and vaccines.
Some of the common factors causing Autism
Autism is proposed to have many causes for its occurrence and still is incomplete. To find the treatment and diagnosis related to autism it’s very important to find its root cause of the occurrence. The researchers have been trying to find its related causes which are different in almost all cases and are treated accordingly. So, some of the common causes of Autism are illustrated below –
A genetic factor is the most significant factor causing Autism. In the early studies on twins by NCBI, the estimated heritability was over 90% which explains that the genetics can predict whether the child will develop autism or not. This research data can vary as the new twin heritability was estimated to be 60-90%.
There are more than 300 genes on a different chromosome which might be responsible for causing autism. Heritability can cause Autism with no recent family history with Autism. The chances of developing autism in a child are also seen due to the de novo mutations in the father’s sperm and mother’s egg. This hypothesis can be supported by 2 lines of evidence and they are,
- The individuals with autism are 20 times less likely to have children than other people and the mutation in the ASD gene persists.
- Due to increased paternal age, the chances of autism increases.
Some other genetic issues causing Autism.
- According to the gender-specific forms of Autism, fragile X syndrome is a type of mutation in boys which consist of autism spectrum disorder.
- MECP2 is a gene which is inactivated by a mutation causing Rett Syndrome. Rett Syndrome is associated with autistic behavior in girl and boys.
- The cognitive and behavioral features associated with the mutation is variable.
Interactions between Genes and the Environment
In case any individual is susceptible to ASD and the reason behind that is a genetic mutation. Then, there are some conditions in that individual which might be the reason for autism.
For example, any person at any time have physical contact with the chemicals or have an infection, then he/she might be susceptible because of genetic mutation. But there is still a probability that he/she might not be susceptible to ASD despite having similar experiences.
Epigenetic is a type of heritable phenotype which may increase the risk of Autism. It doesn’t change the DNA sequencing but is the result of chromosomal histone modification or the modification of the DNA bases. Epigenetic modification is also known to be affected by environmental factors like nutrition, drugs and mental stress.
The prenatal environment involves several risk factor of Autism and the prenatal risks factors like advanced age in either parents, diabetes, bleeding and use of drugs by mother during the pregnancy can cause Autism. In some of the rare cases, autism is also linked with the birth defects during the first eight weeks from conception. Some of the prenatal environmental agents causing Autism are-
Infectious processes like Rubella
Its a non- genetic cause of Autism and the prenatal exposure to Rubella or cytomegalovirus can greatly increase the risk for Autism. Congenital rubella syndrome has higher chances of causing autism at the early pregnancy stage rather than in the late pregnancy and may affect the neural development of the child. It’s not the only way the rubella infection attacks but the psychiatric disorders like schizophrenia has a similar cause. Vaccination against rubella before conception can reduce the chances of autism in the child.
Some environmental agents like Teratogens are theorized to cause birth defects and they also contain the potential autism risk factor but are not supported by any scientific evidence. Teratogens include exposure of the embryo to valproic acid, paracetamol, thalidomide or misoprostol. As the Autism arises very early in development, these all known teratogens appear to act between the first 8 weeks from conception.
Scientists are still working on biological factors apart from genes that may cause ASD. Some of the other factors are-
- A difficulty with growth or overgrowth in specific areas of the brain.
- A disorder related to metabolism (which is the human body energy production system).
- Brain connection related problems.
- Difficulty related to the body’s immune system, which helps in fighting against infection.