What Are The Genetic Causes Of Autism
Studies have shown that autism may run in families and several different genes seem to be involved in ASD.
ASD can be associated with a genetic disorder like Rett syndrome or fragile X syndrome for some children.
For others, genetic mutations could increase risk of the disorder. Also, other genes may be at play in affecting the brain development.
Genes may also be impacting the way brain cells communicate, or may be determining the symptoms or severity.
Research indicates that some genetic mutations are likely to be inherited, while others occur spontaneously.
When a parent is the carrier of these genes, they may pass it onto the child. In this case, the parent does not have to have autism.
Other times, the genetic mutations could happen in an early embryo or the sperm and/or egg that combine to create the embryo.
However, these gene mutations do not cause autism by themselves, but increase the risk of developing the disorder.
Asd Risk Genes Overlap With Other Diseases
Large-scale sequencing studies of major psychiatric diseases have revealed extensive overlap in risk loci, challenging the classification of these conditions as distinctive disorders. In 2013, the Cross-Disorder Group of the Psychiatric Genomics Consortium conducted a massive study with 33,332 cases and 27,888 controls in order to identify pathogenic variants shared between ASD, schizophrenia, bipolar disorder, ADHD, and major depressive disorder . In addition to establishing varying degrees of pair-wise crossover, they found loci that reached genome-wide significance for all five disorders near the following genes: inter-alpha-trypsin inhibitor heavy chain 3 , arsenite methyltransferase , calcium voltage-gated channel subunit alpha1 C , and CACNB2. Glessner et al. have also conducted a large-scale meta-analysis of structural variants across the same diseases and correlated structural variants in the loci of dedicator of cytokinesis 8 and KN motif and ankyrin repeat domains 1 with all five conditions. Schork et al. recently hypothesized that abnormal gene regulation in radial glia and interneurons during mid-gestation is a mechanism of shared risk, after using GWAS to identify susceptibility loci in genes including phosphodiesterase 1A , protein phosphatase 1 regulatory inhibitor subunit 1C , RHOA, immunoglobulin superfamily member 11 , and sortilin related VPS10 domain containing receptor 3 .
Epigenetics And The Environment
Autism susceptibility is currently estimated to be 4080% genetic. Environmental factors likely acting through epigenetic regulation as the major mechanism presumably compromise the remainder of the risk. Hundreds of potential environmental factors have been suggested to contribute to risk, such as increased parental age , maternal complications or infections during pregnancy, or prenatal exposure to anticonvulsants . In-depth reviews of these findings can be found elsewhere . In this review, we will only discuss the epigenetic modifying effects of valproic acid an anticonvulsant as one example of the widespread modifications that an environmental factor can induce. Valproic acid has been hypothesized to modify gene expression through histone deacetylase inhibition activity and is sometimes used to induce an autistic phenotype in animal models . Examples of its far-reaching effects include apoptotic cell death in the neocortex, decreased proliferation in the ganglionic eminence, increased homeobox A1 expression, abnormal serotonergic differentiation via Achaete-Scute family BHLH transcription factor 1 silencing, disrupted serotonin homeostasis in the amygdala, dendritic spine loss, reduced prefrontal dopaminergic activity, and disruption of the glutamatergic/GABAergic balance .
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Testing For Known Genetic Causes Of Asd
Though blood tests are not part of an ASD diagnosis, they can and do come into play to rule out known genetic causes . Having a genetic diagnosis in addition to an ASD diagnosis can help families in several waysmost notably, it can alert them to other potential conditions, including FXS.
Autism and FXS are often diagnosed separately, with many children diagnosed with autism before they are diagnosed with FXS. According to one study, it is naïve and counterproductive to assume that autism is the same in FXS as it is in autism alone, or that the same treatments will work in both cases. In other words: A child diagnosed with ASD would ideally be undergoing treatment for their autism. But if they also have undiagnosed FXS, that treatment would not take their FXS into account. For example, an impairment in social interaction is one of the core characterizations of autism. But since many children with FXS are interested in social interactions, treatments for ASD that focus on the social aspect, may not be productive in the overall care for those with FXS+ASD.
Because of the link between autism and FXS, pediatrician and Fragile X expert Dr. Randi Hagerman recommends that children diagnosed with autism receive a genetic evaluation and testing for FXS and other genetic causes.
Mosaic Deletions And Duplications
The second study was the first large-scale investigation of mosaic copy number variants in children with autism spectrum disorder. CNVs are rare mutations in which whole chunks of a chromosome often containing multiple genes are deleted or duplicated.
A team led by Dr. Walsh, Dr. Park, and Maxwell Sherman and Dr. Po-Ru Loh of Brigham and Womens Hospital looked for mosaic CNVs in about 12,000 children with autism and 5,500 unaffected siblings. Instead of brain tissue, they studied blood samples from the large Simons Simplex Collection and SPARK datasets.
Cutting-edge data-crunching techniques helped the team detect mosaic mutations that likely originated during embryonic development. A handful of these were mosaic CNVs, affecting as few as 3 percent and as many as 74 percent of the blood cells sampled from each child.
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Greater Understanding Of Genetics Of Asd
ASD is a group of neurological and developmental conditions that affect communication and behavior. Theres wide variation in the type and severity of symptoms in people with ASD.
Scientists believe that both genes and environment are involved in the development of ASD, with genetics playing a big part.
We know that inherited and unique mutations in the genome are a major source of risk for developing ASD, but specific causes of ASD are not yet well understood, said Lori J. Warner, PhD, director of the Center for Human Development and Ted Lindsay Foundation HOPE Center at Beaumont Childrens Hospital in Royal Oak, Michigan, who wasnt involved in the study.
Although environmental factors play some role in ASD, scientific have found that theres no link between receiving vaccines and developing ASD.
The new study marks an important step forward in scientists understanding of the genetic basis of ASD.
Researchers identified both inherited genetic mutations and de novo mutations ones that occur spontaneously when an egg or sperm form.
They also found that the ASD genes identified in the study can affect brain development or brain function. And they showed that two major types of nerve cells can be affected in ASD.
Of the 102 genes identified in the study, 49 were associated with other developmental delays.
Zwaigenbaum said the overlap between ASD and other neurodevelopmental disorders fits with previous research.
What Causes Autism And Why Are More And More Kids Being Diagnosed With It
Does a friend or family member have a child with autism? Autism rates seem to be skyrocketing. Among children who are 8 years old, autism has nearly doubled from 1 in 150 to 1 in 68 for children born in 2002.
Autism is part of a larger group of related conditions, called autism spectrum disorders , all of which usually involve delayed verbal communication and difficulties in social interactions. Studies suggest that children with autism tend to have other problems with how their brain functions, with as many as 20-30% developing seizures or epilepsy.
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Causes Of Autism Remain Mysterious
While autism is increasingly common, its cause is usually unknown. In a general way, researchers believe that there is a strong genetic component to autism and that there are environmental “triggers” that may cause certain individuals to develop symptoms for any individual, however, the precise nature of the genetic and environmental triggers is unknown.
When autism is of known origin , it is referred to as secondary autism. When autism is of unknown origin, it is called idiopathic autism.
How Can I Find Out If My Childs Case Is Genetic Can We Tell Which Side Of The Family The Autism Came From
Experts maintain that the cause of autism is largely genetic they attribute about 80% of the risk to inherited genes, leaving only 20% to environmental factors. This is a monumental finding for the causation and treatment for autism spectrum disorder , but much is left to be discovered.
Because no single gene causes autism , there are no genetic tests available to diagnose autism. Many different changes and mutations in a persons genes can lead to them developing autism. However, a genetic test can explain why your child developed ASD, as well as other information that could benefit your family.
If your child has been diagnosed with ASD, our therapists and behavior specialists at Therapeutic Pathways will help them develop and strengthen their social, emotional, and intellectual skills to improve their quality of life.
We are involved in the scientific community and follow the latest research involving genetics and the role they play in autism. Our approach at Therapeutic Pathways is to use evidence-based autism treatment that will help your child live a satisfying and well-rounded life.
Please call 422-3280 or contact us for more information.
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Theories About Environmental Exposures
There has been a rise in cases of autism, and theories about why abound. While there are certainly people who believe there is a connection between some of the following and autism, there is no solid evidence to support this.
- Ultrasound used to monitor fetal growth
- Vaccines given to young children
- Cell phone usage among parents
- Allergies to peanuts and gluten
- Prevalence of Lyme disease
Autism presents itself differently in different people. This suggests a variety of causes and, perhaps, a variety of syndromes with some symptoms in common.
The Curious Connection Between Autism And Cancer
A surprising number of genes associated with autism also have links to cancer. Does that mean cancer drugs can treat autism?
Five years ago, on Charlie Ryans second birthday, a big lump mysteriously formed on the side of his abdomen. At the emergency room his parents took him to, doctors suggested the lump was a hernia caused by some unknown trauma, and referred the family to a surgeon. The surgeon told them it was a benign tumor, and sent them home.
Charlie already had a host of medical issues. Hed been born with an abnormally large head and other features of autism, including being nonverbal. Now this.
Like many a baffled and worried parent, his mother, Autumn Ryan, turned to Google, typing in Charlies ailments and coming up with a possible cause: a mutation in PTEN, a gene that reins in cell growth. Further searching led her to websites dedicated to families whose children have PTEN mutations. It all looked familiar and worrisome. I read stories of little boys who havent lived, descriptions of these children with a multitude of bumps all over their bodies, Ryan recalls. I was freaked out.
In Eng, Ryan finally found someone who understood Charlies condition. Its like going to the person who has all the knowledge in the world, and you can ask her any question, Ryan says of Eng.
Cancer link: The mutation responsible for Charlie Ryans autism, in the PTEN gene, can also lead to cancers.
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Genetic Causes And Modifiers Of Autism Spectrum Disorder
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
Autism Spectrum Disorder is one of the most prevalent neurodevelopmental disorders, affecting an estimated 1 in 59 children. ASD is highly genetically heterogeneous and may be caused by both inheritable and de novo gene variations. In the past decade, hundreds of genes have been identified that contribute to the serious deficits in communication, social cognition, and behavior that patients often experience. However, these only account for 1020% of ASD cases, and patients with similar pathogenic variants may be diagnosed on very different levels of the spectrum. In this review, we will describe the genetic landscape of ASD and discuss how genetic modifiers such as copy number variation, single nucleotide polymorphisms, and epigenetic alterations likely play a key role in modulating the phenotypic spectrum of ASD patients. We also consider how genetic modifiers can alter convergent signaling pathways and lead to impaired neural circuitry formation. Lastly, we review sex-linked modifiers and clinical implications. Further understanding of these mechanisms is crucial for both comprehending ASD and for developing novel therapies.
Genes Involved In Autism: Candidate Genes
Studies on monozygotic and dizygotic twins, adopted children and their families helped the establishment of a strong genetic component in autism. Still, analysis performed on the genome of autists failed in the establishment of consistent signs of linkage. None of cognitive and affective diseases, as well as certain psychoses, follow a heritage pattern according with Mendel’s laws, reinforcing the hypothesis of the involvement of multiple genes .
Since it is a complex disorder with the involvement of several variants, each contributing with a reduced risk to phenotype, the identification of susceptibility genes has been difficult. Moreover, hypotheses that support the presence of synergism and/or epistas is between multiple candidate genes are based on chromosomic changes that are not always enough for disease development . So, traditional methods of linkage used in most studies, are insufficient to detect modest genetic effects, in typically small samples. It is then necessary to select candidate genes based on the type of coded proteins that play an important function in autism development .
A big number of involved chromosomes suffer translocations and inversions. These changes result in interruption of genes as well as deletions and duplications that are responsible for differences in gene expression. The most frequently reported mutations are duplications in 15q11-q13 and deletions in 2q37, although most of them are undetectable by karyotype analysis .
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Is Autism Genetic Or Hereditary
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 todays 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.
Study Points Toward Treatment And Diagnosis
While scientists now understand ASD better as a result of this study, this kind of research also points toward better ways to help children with ASD.
The greatest benefit of studies of this type is helping researchers, families, and interventionists better understand how genetic factors actually function in the developing brain and body of the individual, said Warner, so that treatments can be developed to ameliorate or completely block the disruptive changes that lead to disorders such as ASD.
But Zwaigenbaum cautions that the results of the study will not lead to clinical benefits right away.
Theres a lot of translational work that would still need to happen in order to assess whether the findings from this study will directly inform assessment, diagnosis, or treatment, he said.
Still, he said the results provide direction for future research into potential biological treatments, as well as genetic tests that could allow earlier diagnosis of ASD.
Warner said there are medications currently approved for use in children with ASD, but they address symptoms like agitation or anxiety, rather than the core social or behavioral deficits of ASD.
Early diagnosis is another goal of ASD research, because the sooner children are identified and appropriately assessed, the sooner families can receive needed supports, said Warner.
But ASD is a complex condition, so genetic diagnosis isnt always straightforward.
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Single Mutation Leads To Big Effects In Autism
NIH study provides insight into one mechanism underlying the higher prevalence of males in some cases of autism.
A new study in Neuron offers clues to why autism spectrum disorder is more common in boys than in girls. National Institutes of Health scientists found that a single amino acid change in the NLGN4 gene, which has been linked to autism symptoms, may drive this difference in some cases. The study was conducted at NIHs National Institute of Neurological Disorders and Stroke .
Researchers led by Katherine Roche, Ph.D., a neuroscientist at NINDS, compared two NLGN4 genes, , which are important for establishing and maintaining synapses, the communication points between neurons.
Every cell in our body contains two sex chromosomes. Females have two X chromosomes males have one X and one Y chromosome. Until now, it was assumed that the NLGN4X and NLGN4Y genes, which encode proteins that are 97% identical, functioned equally well in neurons.
But using a variety of advanced technology including biochemistry, molecular biology, and imaging tools, Dr. Roche and her colleagues discovered that the proteins encoded by these genes display different functions. The NLGN4Y protein is less able to move to the cell surface in brain cells and is therefore unable to assemble and maintain synapses, making it difficult for neurons to send signals to one another. When the researchers fixed the error in cells in a dish, they restored much of its correct function.