Sunday, August 14, 2022

Is Autism An Inherited Trait

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There Is A Relationship Between Autism And Brain Activity

Ivan Iossifov discusses genetic variants linked to autism traits

Recent brain imaging studies show that autistic people and typically developing people do not use their brains in the same way. Autistic people do not use their brains to “daydream” in the same way as most people, nor do they process information about faces in the same way. So far, while we know that this information is true, we don’t know what causes these differences — or whether these differences somehow cause autistic symptoms.

Definition And Evolution Of Asd

Autism is a developmental neuropsychiatric syndrome with onset before the age of three. The fundamental conceptualization of the disorder is based on the initial observation of Kanner in 1943 , where he described 11 children with autism, mostly boys with a combination of severe social and variable language dysfunction and the presence of repetitive restrictive behaviors. Kanner made numerous interesting observations based on these case studies, including the identification of large head size in about half of the subjects and postulated a biological, genetic basis for the disorder. However, until the 1980s autism was not considered a distinct disorder in the manuals of psychiatric diagnosis, nor was it considered by most to be biologically based.

Why Do Genetic Studies Matter

If it’s hard to determine if autism is genetic, why do researchers keep working on the answer? Their work may seem futile, but the results matter for families, doctors, and children with autism.

For example, families have long worried about enhanced autism risk sparked by everyday activities. They worry about:

  • Vaccines.
  • A childs dietary habits.
  • Infections, including the flu.

Parents can grow so worried and distressed that they avoid lifesaving steps, including vaccinating children and exposing them to healthy foods. Genetic studies can bring relief.

For example, in a large study in 2019, researchers determined that 80% of autism risk came from genes, not the environment. This news was shared far and wide, and it laid some worries and fears to rest. Parents who blamed themselves for a child’s ASD may have felt relief about the news too.

Gene studies may point the way to treatments and cures too. For example, a researcher duo in North Carolina is working on both detection and cure methods. One part of the pair examines genetic testing, so parents could spot the disorder in kids before symptoms appear. The other examines gene splicing, so damaged bits of data are removed before problems are noticed.

This is groundbreaking research, and it may be years before we hear if the theories translate into real-world solutions. The researchers have a lot of work to do before they can start in on therapies with families.

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There Is A Relationship Between Autism And Brain Structure

Recent brain studies show that autistic brains grow at an unusual rate between the ages one and two and then slow again to a normal rate of growth. Some imaging studies suggest that certain areas of the brain are larger than is typical. Research is ongoing to determine whether these differences in brain structure cause autism, are caused by autism, or are comorbid with autism and caused by something else.

Genetics Play Bigger Role In Autism Risk Than Environmental Factors

What is Autism

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– Most of the variation in risk for autism may be explained by genetics rather than differences in environmental factors like lifestyle or community characteristics or certain pregnancy outcomes, a study in five countries suggests.

Autism spectrum disorder has long been thought to involve inherited genetic traits, and some previous research also suggest that some non-inherited traits and maternal characteristics may also play a role. For the current study, researchers examined data on births from 1998 to 2007 in Denmark, Finland, Sweden, Israel, and Western Australia.

Overall, about 80% of the variation in risk for autism was linked to inherited genetic traits, although this ranged from 51% in Finland to almost 87% in Israel.

The results show that genetic factors are most important but that the environment also play a role, said Sven Sandin, senior author of the study and a researcher at the Karolinska Institute in Stockholm, Sweden

Previous studies have found having a sibling diagnose with autism increases the risk by a factor of 10 to 14, Sandin said by email. And having a cousin with autism doubles the risk.

But knowing genetics influence the risk doesnt necessarily help parents prevent autism in their own families, Sandin said.

Since our results do not tell us anything about specific risk factors or specific genes, there is not much parents can learn to influence the risk of developing autism, Sandin said.

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Is Autism Genetic Study Finds 80% Risk From Inherited Genes

A new study looking at autism in 5 countries found that 80 percent of autism risk can be traced to inherited genes rather than environmental factors and random mutations.

The study, published July 18 in JAMA Psychiatry, analyzed data of nearly 2 million people across Denmark, Finland, Sweden, Israel, and Western Australia. It is the largest family-based genetic autism study to date, including children with autism, their siblings and cousins, as well as parents and their siblings.

We expanded on previous results by including more family members and data from countries that vary widely in their autism health systems, said Joseph Buxbaum, M.D., one of the study authors and professor of psychiatry at the Icahn School of Medicine at Mt. Sinai Medical Center. We found that the strongest contributors to risk of autism are from inherited genes. Spontaneous genetic changes and other factors that we could not estimate are additional contributors to risk of autism.

In addition, the study found very little or no risk resulting from maternal effects such as chronic health conditions that are consistent across all of a womans pregnancies. But for maternal factors that might occur in only one pregnancy, the studys analysis cant separate out those risks.

While the studys authors concluded that maternal effects create no risk for autism, researchers who study these effects say this is a complicated issue.

Can Autism Be Inherited From Siblings

There is a risk that a brother or sister of an individual with idiopathic autism which is of unknown cause might developed autism spectrum disorder is around 4%. Also, there is an additional 4% to 6% risk for a milder condition includes symptoms related to language, social and behavioral.

Brother has a higher risk of developing autism spectrum disorder compared to sister, which is about 7%. Also, there is an additional 7% risk of milder autism symptoms, over sisters whose risk is only about %1 to %2.

The causes of autism spectrum disorder could be divided into two categories. They are idiopathic which is the majority of cases and it is of unknown cause and secondary causes in which a chromosome abnormality. In this case, single-gene disorder or environmental agent can be identified. While approximately 15% of individuals with autism can be diagnosed with secondary autism, the remaining can be diagnosed with idiopathic autism.

When the case comes to the siblings, things mostly depend on secondary autism. When the cause of autism is a chromosome abnormality, the risk that other sibling will also have autism depends on the specific genetic cause.

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When They Occur Together

There may be a reason why symptoms of ADHD and ASD can be difficult to distinguish from one another. Both can occur at the same time.

Not every child can be clearly diagnosed. A doctor may decide only one of the disorders is responsible for your childs symptoms. In other cases, children may have both conditions.

According to the Centers for Disease Control and Prevention , 14 percent of children with ADHD also have ASD. In one study from 2013, children with both conditions had more debilitating symptoms than children who didnt exhibit ASD traits.

In other words, children with ADHD and ASD symptoms were more likely to have learning difficulties and impaired social skills than children who only had one of the conditions.

Identification Of Candidate Asd Risk Genes

Autism Genetic Research Breakthrough

Following the classification of autism by Kanner, research efforts were undertaken to determine the disease etiology. Though it was initially assumed to be of environmental origin, an improved understanding of the role of genetics in human health soon suggested otherwise. In 1977, Folstein and Rutter conducted twin studies upon the observation that incidence among siblings was 50× higher than average. They found that monozygotic twins were more likely to share a diagnosis than dizygotic twins, suggesting a genetic influence. Bailey et al. supported this finding, documenting 60% concordance for monozygotic twins versus no concordant dizygotic pairs. In addition, risk of a child having ASD was found to be proportional to the percentage of the genome they shared with an affected sibling or parent . By the turn of the century, ASD was established to have some genetic component, though which genes were involved remained a mystery.

Somatic Mosaicism and ASD Risk

CNVs Contribute to ASD Susceptibility

Epigenetic Regulation and ASD

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Genes The Role They Play In Our Lives

Fig 1

The continual investigation being done in the field of autism has led researchers to seek answers to whether autism is genetic. Over the last decade or so, the U.S Department of Health and Human Services has been generously propelling funds to research in the field of Genetics and Genomes genetics being the study of individual genes while genome is the study of the entire gamut of genes in a human system.

In the Figure, X & Y represents Male or Female. The remaining 22 genes are common to both genders.

Did you know: While a human has 23 pairs of genes, a firefly has only 4. Think of the massive array of genetic combinations across all life forms known to man!

According to researchers, Genes are the basic unit of human composition and are acquired through heredity. A genome is like an instruction manual that determines what species an organism will belong to. Most people, however, are more familiar with the scientific term DNA which is a combination of these genes that provides unique characteristics to every individual within that species it is our unique racial security number. For example, you and I are made of the same Genome but our DNA composition would be distinctively unique.

What Can Families Do Right Now

Your family doctor can’t offer you gene splicing. Some can’t even provide genetic counseling. If you have autism and you are considering having kids, know that your children may have the same condition you do. If you don’t have autism but someone in your family does, the risks may still be enhanced for your child.

If you have a child or loved one with autism, watch the results of studies. Talk over questions with your doctor. Look for ways to support charities that fund autism research. The more we know about this disease, the better.

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No One Factor Causes Autism

It is unlikely that any single factorvaccines, foods, or environmental toxinsis the cause of the steep rise in autism diagnoses. “To find clues about the cause,” says Dr. Croen, “we have to do really large studies to look at different configurations of co-morbidities see whats unique about each separate group.” New research will be addressing the questions “How do these circles overlap? What is the common thread?”

Genetic Effects Stack Up In Some People With Autism

Autism Genetic Disorder

Laura DattaroMultiple hits:

Rare genetic variants that alter the expression of genes in the brain contribute to autism in people who also have a rare autism-linked mutation, according to a new study. The findings help explain how some second hits drive autism in people with known mutations, the researchers say.

The study analyzed families carrying deletions of DNA in the chromosomal region 16p12.1. About 30 percent of people with this deletion are autistic 90 percent inherit the mutation from a parent, who often has mild or no neuropsychiatric traits.

Children with autism and the 16p deletion who carry other genetic variants often inherited from the parent without the deletion tend to have more profound traits than those without second genetic hits, the researchers showed in 2018.

Unpublished work from the same group supports those second hit findings: In an analysis of 113 families with the deletion, carrier parents tended to have different and often milder neuropsychiatric traits than their carrier children. The researchers presented the work at the 2021 American Society of Human Genetics meeting last month.

The new work shows that the second hits in the children affect autism traits largely through altering the expression of other genes.

There could be a lot of things going on, but in general, family history plays a major role, Girirajan says.

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Genes Probably Interact With Environmental Factors

It is likely that genetics and environmental factors interact to cause autism. As yet, there is no proof of which environmental or genetic factors are to blame. Says Dr. Croen, autism “You need some kind of genetic susceptibility then you have to be exposed to something which is elusive at the moment. This would be the impetus that sends you into autism.”

Social Environmental Changes And Decanalization

The decanalization concept may have sizable significance in searching the cause of the maintained or increasing prevalence of ASD. Canalization is an evolutionary phenomenon characterized by robustness to genetic or environmental perturbation, and most individuals tend to cluster around the optimal phenotype in canalized populations . If the phenotypic dimension consists of multiple endophenotypic vectors which have nonlinear relationships to each other and are partially determined by genetic factors, overt environmental perturbations for one of the endophenotypes can be the cue of decanalization, which changes the shape of the phenotypic demensional distribution . Social environmental perturbations may also shift the entire distribution of ASD liability, or move the liability threshold.

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What Doesnt Cause Autism

Bad parenting

There was a bleak period in history from the 1950s to 1970s when autism was believed to be a psychological disorder, and blamed on cold, uncaring parents, usually the mothers.

Fortunately, the myth of the ârefrigerator motherâ has been debunked by science, and autism is now recognised as a disorder of brain development with genetic links. Nothing you said or did as a parent caused your child to develop autism, so please donât listen to anyone who suggests otherwise.

Vaccines

Scores of scientific studies have effectively ruled out vaccines as a cause of autism. Concerns originally arose around two issues of Mercury and the MMR Vaccine

In 2014, a meta-analysis, combining the result of 10 studies and over 1.2 million children, found no link between vaccines and autism. The World Health Organization, the European Medicines Agency, the American Academy of Pediatrics and other leading international health groups have also concluded thereâs no link. Unfortunately, the belief persists among anti-vaccination campaigners, who are very vocal on the Internet. If you remain concerned about vaccines, arrange a time to talk your paediatrician or GP. Remember, Vaccines Save Lives!

The Molecular Diversity Of Asd

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Several recent reviews summarize the growing list of dozens of common and rare genetic variants that have been associated with ASD at varying levels of statistical evidence , so I refer the reader to these reviews for comprehensive gene lists. Here, instead, I will try to synthesize what these findings may be telling us about ASD pathophysiology at what is still an early juncture in the search for ASD susceptibility genes.

The most obvious general conclusion from all of the published genetic studies is the extraordinary etiological heterogeneity of ASD. No specific gene accounts for the majority of ASD, rather, even the most common genetic forms account for not more than 12% of cases . Further, these genes, including those mentioned earlier, represent a diversity of specific molecular mechanisms, ranging from cell adhesion, synaptic vesicle release and neurotransmission, synaptic structure, RNA processing/splicing, and activity-dependent protein translation. On one hand, this should not be surprising, as autism is defined based on observation of cognition and behavior, not etiology. On the other hand, the diversity of potential mechanisms and the apparent lack of specificity of mutations for ASD begs the question as to whether ASD should even be viewed as a unitary disorder. Therefore, asking whether the diverse genes implicated in autism might converge on common pathways becomes an important question for understanding autism and developing new therapeutics.

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Converging Circuits And Common Pathways

Convergence of pathways may be assessed at many levels, ranging from molecular mechanisms to brain circuitry. The earliest synthetic molecular model was based on the notion that the primary area of convergence in ASD was the postnatal, experience-dependent development of the synapse . This was a highly productive model based on several forms of Mendelian mutations in ASD, which has led to successful exploration of synaptic scaffolding molecules and other synaptic genes as ASD susceptibility genes . Interestingly, because many mRNA for synaptic genes are alternatively spliced, and the proteins regulated by ubiquitination, this paper was prescient in predicting alterations in mRNA splicing and ubiquitination pathways that have since been identified . Nevertheless, since the synapse is integral to the function of all neurons, how the cognitive and behavioral specificity of ASD emerges, distinct from ID or other synaptic disorders, is not yet explained by this molecularly focused model.

Convergence of genes on neural systems

Clinical Implications And Future Perspectives

When autism was first described, it was hypothesized to be an environmentally caused disease. Decades of research have since revealed that autism is a highly heterogeneous and extremely complex genetic condition. Even though great progress had been made in identifying hundreds of risk genes, very little is known about the different types of modifiers that may exacerbate or ameliorate disease severity. Such modifiers could include epigenetics, sex-linked modifiers, CNVs, double-hit mutations, or environmental factors .

Figure 1. Genetic modifiers in autism spectrum disorder. Autism is estimated to be 4080% heritable. However, both genetic and non-genetic factors modulate the penetrance of risk genes, resulting in a highly heterogeneous disease phenotype for similar pathogenic variants. Examples of genetic modulators include CNV, epigenetics, and double-hit mutations. Examples of non-genetic modifiers include environmental exposures and sex-linked modifiers.

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