The heritability of autism spectrum disorder is the proportion of differences in the expression of autism that can be explained by genetic variation. If the heritability of a condition is high, then we can consider the condition as a primarily genetic. Genetic factors occupy the most important place among the causes of autism spectrum disorder.
In today’s world, it is not known what exactly causes autism spectrum disorder, but there is evidence that it is genetically based. However, it is not yet known which gene or genes are responsible for this condition. There are opinions that environmental factors can also lead to autism. Numerous studies have been conducted on the effects of both genetic basis and environmental factors.
Autism is hereditary. The combination of genetic and environmental influences is known to cause autism. It is estimated that about 80 genes cause autism. Only a few of these genes have been found to date. Studies on this subject continue. Despite this, it is not yet possible to diagnose autism during pregnancy. Having a child with autism has nothing to do with how you raise them or what economic conditions you have. For this reason, autism spectrum disorders are observed in all kinds of societies, different geographies, races and families.
Early studies on twins have shown that the inheritance of autism is very high. In other words, genetic factors have shown that it can explain most, or almost all, of autism cases. More experiments and studies need to be done to confirm these. To confirm this prediction, twins need new data and structural genetic models. If only one twin has autism spectrum disorders, the others usually have learning and social disabilities. For adult twins, there is a significant percentage, although the risk of having one or more features of broader autism is not very high.
The genetics of autism is complex. Genetic linkage assays were unsuccessful up to this time and many assays were not sufficient. There may be mutations in more than one gene for each individual with autism. Mutations occur in different sets of genes in different individuals with autism. There may be interactions between mutations in various genes or between the environment and mutated genes.
Many family studies have been conducted investigating the effect of genes on autism. Several groups of candidate genes have been identified, whose proteins associated with neuro system development and function are inherited by autism. However, a mutation that increases the risk of autism has not been found among them. Autism does not consist of a typical single chromosome abnormality like other diseases. Deletion, duplication and inversion are chromosomal abnormalities associated with autism.
Let’s say that individuals with autism do not have anyone with autism in their families. These individuals may have this condition due to the variety of mutations in their genes. To understand this, non-hereditary cases were examined. Genetic locus candidates related to autism were tried to be determined. But the studies did not yield sufficient enough results.
There are many studies conducted about the heritability of autism. Some of them specifically about the genetic-hereditary effect of autism. The prevalence of autism in siblings of children with autism is between 10-18%, which is well above the prevalence in society. In identical twins, this rate is between 60 – 90%.
Introversion, difficulty in social relations and problems in language development are more common in the families of children with autism compared to other families in society. Despite these findings pointing to the genetic basis of the problem, the mechanism that causes autism has not been fully elucidated.
The effect of some genes is emphasized and intensive studies are continuing in this field. There are multiple genes that are thought to be effective in social interaction and communication functions. It is thought that the failure that exists in several genes, not in any of them, constitutes the basis of autism spectrum disorder.
There is no valid reason for autism in children diagnosed with an autism spectrum disorder. Medical elements are identified in a certain number of children with autism. The risk of having autism in siblings of children with autism varies between 10 and 18%. In the case of someone with autism in the family, this risk was found to be up to 32%. In addition to medical factors, behavioral factors and family environment are also effective in autism. Research on autism shows that the brains of individuals with autism work differently. There is a problem with the transmission of chemicals in their brain cells and the chemical balance in their brains.
Three different studies conducted by professors at Yale, Harvard and Washington Universities in the USA indicate that the risk of autism in children increases with the age of the parents, and this risk is higher especially for fathers who are over 35 years old. Scientists have stated that the new research will help them to establish the right strategy to understand the biological basis of autism and that they have not had such opportunities in the past. In addition, after decades of discussion of hereditary risks of disorder and its association with environmental factors, autism has been found to have a strong genetic basis.
Researchers have reported that these genetic mutations are very rare and very few of the children involved in the research have these mutations. It is stated that 15-20 percent of all cases of autism can be understood by deciphering very rare genetic mutations and new mechanisms can be obtained in understanding the problems in brain development.
These three studies, which can be considered as a turning point in autism research, focused on rare genetic disorders known as de novo mutations. The genetic material in the blood of parents of children with autism was analyzed, although they did not have any symptoms. Thus, instead of examining the genetic characteristics that may have come from the parents, it was aimed to identify the first mutations that could cause autism.
Although de novo mutations are not hereditary, they can occur naturally in early pregnancy or during pregnancy. Most de novo mutations found in many people do not pose a threat to physical and mental health.
In the first study, de novo mutations were tried to be detected in 200 people who were diagnosed with autism and did not show signs of autism. The study identified de novo mutations in the same genes in two children with autism who were not related to each other. The similarity was not found in people without a preliminary diagnosis of autism. The result is like hitting the same spot twice on a dartboard with 21,000 dots. The mutation detected gene is a 99.9999 percent chance of causing autism. A de novo mutation was detected in a different gene in a third child with autism. However, it is stated that this gene is less likely to cause this neurodevelopmental disorder.
Similar to the previous research was conducted on 209 families. In this study with the same result, a child with autism was found to have a genetic disorder in the same gene. The similarity in the two studies was not limited to this. The researchers found that two unrelated children with autism had a de novo mutation in the same gene. A similar situation was not observed in the studies conducted on people without autism.
A third and similar study was conducted. Researchers trying to find the three genes in the first two studies found more cases carrying these genes. Each person has at least one de novo mutation in general. However, in this study, it was found that children with autism had these mutations at a higher rate and the effects of the mutation were much stronger.
All three studies have shown that the risk of autism increases with the age of parents. An analysis of 51 de novo mutations revealed that the DNA in men is four times more likely to cause genetic defects than women. The increase in the risk of having a child with autism in 35-year-old men compared to 25-year-old men revealed the effect of the age factor.
Scientists based the effect of age difference on the possibility that older men’s sperm may cause genetic disorders that may affect brain development. Findings indicate that the new treatment method will take a long time. However, researchers have suggested that the interaction of high-risk genes in shared biological processes may reduce the process of finding treatment.
Researchers believe that these studies are a breakthrough. Because of the fact that they expected similar results. It could still be a turning point. They believe they can discover 20-30 or more genetic mutations in the next few years. On the other hand, some researchers argued that the genetics of very rare mutations would be deciphered by making the subject more suspicious, and no definitive explanations could be made about the effects of these mutations on certain genes.
The findings show that the impact of environmental factors is smaller. This is important because some parents worry that things like high pollution can cause autism. The general opinion is that the current increase in diagnosis is due to increased awareness. Cases that have been described as learning disabilities in the past are now correctly diagnosed with autism.
Several studies emphasize that autism occurs as a result of the mutation of a gene on the X chromosome. Genetic disorder when the child is in the womb may cause autism. Disruption of genes can also be caused by drugs and radiation. It is stated that the disruption of genes related to communication and social interaction will cause this situation.
These conditions explain the genetic cause of autism but are not sufficient enough to understand autism alone. The debate on why and how autism occurs continues. There is a consensus that many factors in autism lead to autism.
Deformations in the brain that develop due to children’s illnesses can cause autism. Possible causes of autism are such as the age of the mother and father and the lack of vitamin D in the mother. Problems during birth are among the causes of autism. Autism may occur as a result of brain damage in cases where the baby is deprived of oxygen and blood flow is not fully ensured.
The impact of environmental factors is a highly controversial issue. Much has been said about the effect of vaccines and nutrients on autism spectrum disorder, on the other hand, there is no scientific evidence for such a relationship.
Autism has increased much more rapidly today. Autism can be detected in about one in every 68 children. Environmental factors such as metal-based vaccines, various virus vaccines, excessive use of metal-based drugs, the widespread use of antibiotics, insufficient intake of omega-3, and inadequate cleaning of nutrients from pesticides and heavy chemicals are also effective in the emergence of this condition. Children with autism also have various digestive problems. Nutrition of children with autism is also very important in this regard.
Autism, which causes problems in social communication, often occurs as a result of genetic problems. Therefore, if one of the twins has autism, it is highly likely to occur in the other. Some health problems may also be associated with autism. These include muscle dystrophy, an inherited disease that causes muscles to slow down. Down syndrome, another genetic disorder, is also associated with autism. This disorder causes learning disability and physical changes in particular. Cerebral Palsy, Infantile Spasms, Neurofibromatosis, Fragile X Syndrome, Tuberous Sclerosis and Rett Syndrome are other disorders associated with autism.
Genetic Testing for Autism Spectrum Disorder
In today’s world, unfortunately, there is no genetic testing to detect autism spectrum disorder before birth, when the baby is in the womb.
We need to know that autism spectrum disorder is first and foremost a genetic disorder. Most of the risk of autism comes from genes. Mutation in genes causes this condition. While there are four types of tests that can detect these mutations, there is no definite specific test that can diagnose autism.
Genetic tests used to detect other genetic disorders in the womb cannot be used to diagnose autism. Because environmental factors are involved in autism and a situation after the test can change the result. It does not mean that there are hundreds of mutations that lead to this situation, but not every gene mutated causes autism.
Let’s say the genetic test was applied and you got a negative result. But after your baby was born and raised, you learned that he had autism. This is a very livable scenario. The genetic tests in question may not be receiving a particular mutation, or there is no relationship with autism at the time of the test. For this reason, most genetic testing facilities reanaly the results once a year based on the latest findings.