In today’s world, it is not known what causes the autism spectrum disorder, but there are findings that it is genetic-based. However, it is not yet known which genes are responsible for having that. There are opinions that environmental factors can also lead to having autism. Numerous researches have been conducted on the effects of both genetic basis and environmental factors.
Genetic specialists analyzed DNA samples with neurodevelopmental disorders of 16,000 people and found that females diagnosed with autism spectrum disorder on average had from 1.3 times to 3 times more malicious genetic changes than males with a diagnosis of autism.
The findings suggest that with the development of the male brain, smaller and finer genetic changes can trigger autism spectrum disorder. Women’s brains proved to have a greater number of mutations before symptoms could be seen and therefore the symptoms tended to be worse.
The researchers said that the analysis of inheritance dynamics in families is extremely helpful in understanding autism, although it explains that it is not an application for treatment. In addition, 800 families with someone with autism in their homes were participated and examined. As a result, it was discovered that children generally inherited autism-related gene mutations from their mothers.
Although the genetics of autism spectrum disorder is complex, there is a strong genetic basis and it is not clear whether autism spectrum disorder is explained more by various genes interactions or by rare gene mutations with major effects.
The first studies which are done in order to identify chromosomal regions and loci that may cause autism are in the form of connection and relationship studies. No single major gene responsible for autism has been identified in connection or association studies to date. This indicates that autism is a complex genetic disease and shows heterogeneity.
In recent studies aiming to illuminate the etiology of autism spectrum disorder, genetic, brain functions, neurochemical factors, and immunological factors are prominent. Autism should be considered as a heterogeneous disorder because it shows that the clinical course of the disorder has a wide phenotype when the findings in the fields of social relations, communication and behavior are classified as mild, moderate and severe.
In the case of developmental disorders of the brain, men and women are not created equally. Studies which were conducted over decades have shown that men have more risk of neurodevelopmental disorders such as autism spectrum disorder than women have.
Boys are 5 times more likely to have autism spectrum disorder than girls do. The reason for this inequality is still being researched. Since women have a much higher level of tolerance for harmful genetic mutations, the rates of showing autism are much lower than that of men.
While many children with the same genetic mutations may show symptoms of autism spectrum disorder, a girl may show no symptoms. However, since the female mutation threshold is higher than male mutation threshold, girls may tend to fall to the more severe end of the spectrum when they are diagnosed with autism.
When taking a look at the prevalence of autism among boys and girls, it is observed 4 times higher in boys than in girls. Girls with autism spectrum disorder are more likely to be associated with severe mental retardation.
In addition, there is a comparison between girls with autism and boys with autism in the case of language and cognitive problems. Girls with autism have more language and cognitive problems than boys with autism. Moreover, the risk of having autism in the second child of the family varies between 4% and 10%.
Researchers are closing step-by-step to understand why men are more than 4 times affected by autism spectrum disorder. A study conducted by a team of scientists in Toronto found that men carrying specific genetic changes on the X-chromosome carry a high risk of autism spectrum disorder or related to the development of autism spectrum disorder. Scientists have stated that they are working on the gender trend in autism spectrum disorder and found an indicator that explains the reasons behind that.
According to recent studies, researchers have found that about 1% of men with autism have mutated related to the PTCHD1 gene in the X-chromosome. Males inherit the X chromosome from their mother and the Y chromosome from their father. The risk of having autism spectrum disorder or mental retardation would be high if the PTCHD1 gene on a child’s X-chromosome or other nearby DNA sequences is missing.
Even though a PTCHD1 gene is missing in girls, they are always protected from having autism by carrying a second X-chromosome by nature. However, this may occur as a result of autism in women in their future life, during pregnancy or in their children.
Autism spectrum disorder varies with the degree of neurological disorder. However, it often involves deficiencies in communicating with others, unusual patterns of behavior and mental retardations. While the mutation of PTDH1 occurs in 1% of men with autism, it is not present in thousands of healthy male DNAs, and also the sister of the male with the same mutation may not be affected by the symptoms of autism.
Individuals with Autism Spectrum Disorder May Inherit DNA Mutation from Their Father
There is not a single gene that causes autism spectrum disorder when mutated. In the last decade, however, researchers have described hundreds of gene variations that affect brain development by increasing the risk of having autism. However, these scientists have basically studied variants in DNA that directly encode the building blocks of proteins.
A new study, now called non-coding DNA, found that changes in regions that regulate gene activity may also be associated with autism. And surprisingly, these variations tend to inherit from non-autism fathers.
Genetic risk research for autism basically focuses on how the mutations that occur spontaneously in an individual’s genome, rather than being taken from a parent, disrupt the protein coding regions and cause this situation. Because, according to the researchers, these sporadic mutations have relatively large effects, and studies have shown that these rare mutations contribute about 25 to 30% of cases. However, only 2% of the genome consists of protein-coding areas. It has been observed that the largely non-coded part of our DNA has been ignored so far in autism research, previously called trivial DNA.
Researchers were particularly interested in parts of non-coding DNA that regulate gene expression. They looked at all genome sequences from 829 families, including individuals with autism, normally developed siblings and normally developed parents. Evaluation of the effects of individual DNA base changes is more difficult, especially in non-coding regions. Thus, it has been defined that larger changes, which is called structural variants, in which large DNA sequences were reversed, transcribed, or removed.
Each individual has thousands of structural variants in his genome. Therefore, researchers have narrowed their analysis to study a handful of regulatory regions that appear to cause deterioration of genetic diversity. They have found the regions where the general population has less variation than expected and chose them. This suggests that genetic changes can be harmful. These include sites that regulate gene activity during brain development and initiate the transcription of genes.
Scientists then examined whether structural variants in these regions were associated with autism by examining the mode of transmission from parents to children with autism spectrum disorder and normally developed children.
The researchers assumed that mothers were more likely to cross autism-inducing gene variants. Because the rate of having autism is lower in women compared to men, and women are thought to be able to carry the same genetic risk factors without autism. But when a mother passes on these genes to their sons, they are not protected like this way and they are affected.
Researchers suggested that only half of the structural variants of the mothers were transferred their genes to children with autism, namely only by chance and that the variants inherited from the mothers were not associated with autism. However, surprisingly, fathers inherit more than 50% of their variants. This suggests that children with autism can take risk variants in regulatory regions from their fathers, not from their mothers.
In order to check that this result was going on, the researchers then tested a second larger sample of the 1771 families. Once again, children with autism spectrum disorder received a more structural variant from their fathers instead of from their mothers, but in this second example, the effect was not as big as the first one.
Mother’s Genes Could Be the Reason Behind the High Prevalence of Autism Among Boys
Boys have more inclination than girls do in case of getting diagnosed with a neurodevelopmental disorder, for example, autism spectrum disorder. Because of the fact that, according to one study, girls need more extreme genetic mutations in order to develop those kinds of disorders. There is a huge mystery about this issue in child development. Researchers wonder about why so many boys are diagnosed with developmental disorders compared to girls. And, they put their effort in order to search for this.
There is a fact that boys are more likely to develop autism spectrum disorder (ASD), intellectual disability and attention deficit hyperactivity disorder (ADHD). In one study, researchers highlight that 1 girl is getting diagnosed with autism for every 4 boys, while 30% more boys have intellectual disability than girls.
It has been suggested that genetics as well as the possible social bias that increases the chance of getting the diagnosis in boys as a reason for the difference between diagnosis rates of girls and boys. On the other hand, boys are tested more frequently for such disorders, leading to higher rates of getting diagnosed. According to another study, although this research does not identify a social explanation for the gender difference in the diagnoses of neurodevelopmental disorders, the social bias could still be a real effect of it.
To some extent, there are some reasons, such as historical, religious and social, that would lead to more boys being identified with such problems. Even if we do not observe as much of this in modern western societies, there are still glimpses of it. However, on the other hand, researchers suggest that the size of the difference may be attributable to genes.
There is a study which was conducted with nearly 16000 individuals with neurodevelopment disorder. They analyzed DNA samples and sequencing data sets of them. Also, about 800 families which were affected by autism spectrum disorder has involved in this study. Researchers studied the individual variations in the number of copies of a particular gene as well as sequence variations which is affecting single genes.
As a result of this study, it was found that females were diagnosed with autism or any other neurodevelopmental disorder had both a larger number of harmful individual variations and sequence variations compared to similarly get diagnosed males.As the data indicate that, for brain development in order to be knocked off the typical course as is the case for autism spectrum disorder, females need greater more genetic mutations than males.
Due to the fact that women are more developmentally resistant and needed more extreme mutations in case of genetics in order to push them over the diagnostic threshold. Women can accumulate more genetic damage before they present with neurodevelopmental disorders.
There is an amazing fact that there are good evolutionary reasons to protect women, in light of the fact that women are the ones who carry the species. However, these females who survive and have children may inherit the mutations to genes after them. These finding may lead to the development of more sensitive and gender-specific approaches for the diagnostic screening of neurodevelopmental disorders.
Furthermore, there s a question mark about what proportion of the mutations leading to neurodevelopmental disorders which are coming from mothers remained. There would be huge ramifications on diagnostic testing while working out the significance of the mechanisms. One of the next great mysteries was to figure out why males were more genetically fragile than females.
There is a debate about being genetically fragile. Some researchers asked whether, during brain development, females have some form of biological shields that males do not which protects them against a certain number of genetic mutations or not. On the other hand, they also asked whether males have an additional biological mechanism that females do not which may increase fragility to genetic mutations.
According to the same researchers, understanding these questions may lead to very well get to the very heart of what causes various types of autism spectrum disorder and other neurodevelopmental disorders.
Gene Testing for Autism Spectrum Disorder
The discovery of a gene associated with an autism spectrum disorder, which is one of the neurological developmental disorders of unknown cause, has created hope in the medical world. Gene testing of autism may be possible with the help of the gene, which may lead to finding the cause of the disease.
For the first time, researchers have discovered a gene that is linked to autism. The present invention may lead to genetic testing for autism. Children with a mutated CHD8 gene have larger heads, wider eyes, and these children often experience gastrointestinal problems. In addition, these children may also have sleep problems.
In a study in which 13 research institutions from all over the world collaborated, experts examined more than 6000 children with an autism spectrum disorder. In 15 of these children, it was observed that CHD8 was mutated. All of these 15 children had similar physical characteristics. The researchers confirmed the results with experiments on zebrafish. It was determined that fish treated with CHD8 gene were born with a larger head and wider eyes. The zebrafish, which was later mutated, was fed with food that showed fluorescence and was found to have constipation problems.
Researchers say this is a research that can change everything. These results are thought to lead to the discovery of hundreds of genes associated with the developmental disorder which is autism. According to the researchers’ estimates, after a while families will be offered gene testing. This test will help inform families about what to expect and how to deal with children with autism.
Genetic Testing for Autism Spectrum Disorder During Pregnancy
Currently, there is no test to predict the probability of having a child with autism during pregnancy. Recent researches show that if the mother has a child with autism before, it means the risk is higher. The second child would have an autism as well. On the other hand, the risk of having autism in the general population is very low.
In other respect, we all know that it would be highly desirable if a prediction based upon physiological measurements might be made in order to determine which risk group a future mother falls into. There are researches which are done by working in developing a physiological test in order to predict the risk of having autism spectrum disorder.
There is a study which was conducted with pregnant mothers. Their blood samples were measured in order to determine whether the risk of having a child with autism could be predicted by the mother’s metabolic profiles or not. Pregnant mothers who have a child with autism before were separated into 2 groups. This separation was done based on the diagnosis of their child, it means whether they a child with autism or not. And then, there was a comparison between these mothers and a group of control mothers who do not have a child with autism before.
As a result of this study, the researchers concluded that even it is not possible to determine during pregnancy, differences in the plasma metabolites are indicative of the relative risk for having a child with autism. This relative risk varies from person to person with several factors. These are the exciting results because they hint at differences in some metabolic processes. These differences potentially play a role in the understanding of increasing the risk of having a child with autism.
Can Autism Spectrum Disorder Be Treated with Using New Genetic Techniques ?
Autism is a type of disorder in which new treatment methods are being studied. Currently, the most popular and promising method of treatment is gene therapy. However, the genetic structure of the disorder is so complicated that time is needed for the implementation of gene therapy.
In addition, there is a method in which cognitive problems and core symptoms have been investigated in autism. This method is Transcranial Magnetic Stimulation, in short TMU. With this method, it is aimed to increase the learning speed and to alleviate the symptoms by making magnetic stimulation in the frontal region. In some hospitals, TMU was started to be applied to children with autism and after 20 sessions of TMU sessions, increases in the rate of learning and utilization of training were observed.
There is a study which is showed that repetitive actions commonly observed in children with autism could stop with the brain from changing its way of working. Scientists think that using state-of-the-art technology in order to regulate DNA, it can reduce physical tics, such as back and forth from autism, or swinging arms which is observed as a result of having autism.
The gene editing process involves altering the DNA to alter the physical properties within the brain, which means, habits of people that lead to impulsive behavior. Successful research technique which is done on laboratory mice has shown that it can reduce symptoms that are caused by one of the most common forms of autism by as much as 70%.
The mice with autism spectrum disorder used by the researcher in the study had obsessive habits such as digging or jumping in the air. In the study, a special enzyme was sent to the brain of the mouse, in which it changed the mouse DNA, a process called CRISPR gene regulation. DNA is a series of chemicals and the process works effectively by reorganizing the array. And then, it changes the genetics of the mouse. As a result, this can change the physical features of the animal.
Scientists reduced the digging behavior of mice by about 30%, as they worked by regulating the genes of a particular part of the brain. Researchers stated that the gene scheme was used for the first time as this way. The study leader of the research said that “There is no treatment for autism yet. Most of the clinical trials of small molecule therapies targeting autism-induced proteins have failed. This is the first case in which we can regulate a causal gene for autism in the brain and recover behavioral symptoms.”
Researchers think that CRISPR can be used to cope with other brain problem or brain-related problems, such as drug addiction, schizophrenia or epilepsy. They hope to find ways in order to deal with an autism spectrum disorder, which is thought to affect more than 1 in 100 children.