What Genetic Testing May Tell You
Genetic testing cannot tell you anything definitive about autism at this point; it may be able to tell you about some other genetic conditions, should you be concerned. One of these tests may inform you of:
- The chances that your future children may develop autism.
- What kinds of services and treatment may best benefit your child.
- Other health issues or concerns related to the genetic mutation that caused your childs autism. Some genetic disorders have been associated with autism. These include tuberous sclerosis, benign tumors that grow on the brain and other organs, and Fragile X syndrome, a condition that causes intellectual disabilities.
What Does It Mean To Have Just A Hint Of Autism
Comedian Jerry Seinfeld stepped into a minefield when he diagnosed himself as being on the autism spectrum “on a very drawn out scale.” Some applauded the attention he brought to autism, while others, including parents of children with severe autism, complained that he trivialized the real problems of a real disability. How can someone who achieved fame by lampooning social foibles really have anything in common with people who struggle with basic social functioning?
In an interview with NBC news, Seinfeld said he has trouble paying attention “to the right thing,” “basic social engagement is really a struggle” and he finds figures of speech confusing.1 He later clarified that he doesn’t have autism,2 but his remarks left one lingering question. Were these faint whispers of autism he described similar to what researchers call the Broader Autism Phenotype, or BAP?
People with the BAP have some traits common to autism spectrum disorder , but not enough to have the disorder. But it’s not comedians who have drawn scientific scrutiny for having the BAP: it’s the parents and siblings of people who actually have autism.
What is this autistic-like condition, and how can you measure it? Is understanding this condition important for understanding autism? Or is BAP just another example of the over-medicalization of personality traits especially when they belong to the parents of children with autism.
Autism Genetics: A Decade Of Progress
In many ways, autism is a mysterious disorder, as it involves core abnormalities in social cognition and language, both of which are central to what makes us human. Because of this, understanding autism will have a significant impact on our basic knowledge of these fundamental cognitive processes, in addition to the obvious critical role that such mechanistic understanding has on therapeutic development. Until the last decade, virtually nothing was known about the neurobiological basis of ASD. There was no consistent neuropathology and only scant knowledge of a few causal genetic factors. The last decade has brought an explosion of genetic findings in ASD, surpassing most other common neuropsychiatric disorders, so that we now have knowledge of the etiology of ASD for between 1020% of cases. Here, I review these exciting findings with respect to what they tell us about the genetic architecture of ASD and how this informs our mechanistic understanding of the disorder and its relation to human brain function.
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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.
Genetic Tests For Autism Can Sometimes Change Lives
The assays don’t always yield results, but the information they offer can, at times, alter the course of treatment or prevention
Almost as soon as James was born in April 2003, it was clear that he was not well. When he failed a newborn screening test and was struggling to breathe, he was sent straight from the delivery room to the neonatal intensive care unit. Doctors there suspected he had a genetic condition, but genetic testing, such as it was 15 years ago, yielded no answers. So nine days later, James mother, Angela, took him home.
As an infant, James struggled to eat and never slept for more than 20 minutes at a time, but Angela attributed these things to his being a newborn and to the stress of their cross-country move. He didnt sit unassisted at 1 year or crawl until he was 18 months old, but doctors and friends reassured her he was fine. When James was 14 months old, a physical therapist acquaintance took one look at the child and told Angela he clearly had some sort of developmental delay. But even the specialists she then took her son to see dismissed his loud squeals, hand-flapping and tendency to ignore others as consequences of his poor hearing. He was finally diagnosed with autism at age 4.
Even so, most autistic people and their families never gain access to that information: In the United States, roughly one in three children with autism;is offered genetic tests.
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What Is Autism Spectrum Disorder
Autism spectrum disorder refers to a group of complex neurodevelopment disorders characterized by repetitive and characteristic patterns of behavior and difficulties with social communication and interaction. The symptoms are present from early childhood and affect daily functioning.
The term spectrum refers to the wide range of symptoms, skills, and levels of disability in functioning that can occur in people with ASD. Some children and adults with ASD are fully able to perform all activities of daily living while others require substantial support to perform basic activities. The Diagnostic and Statistical Manual of Mental Disorders includes Asperger syndrome, childhood disintegrative disorder, and pervasive developmental disorders not otherwise specified as part of ASD rather than as separate disorders. A diagnosis of ASD includes an assessment of intellectual disability and language impairment.
ASD occurs in every racial and ethnic group, and across all socioeconomic levels. However, boys are significantly more likely to develop ASD than girls. The latest analysis from the Centers for Disease Control and Prevention estimates that 1 in 68 children has ASD.
New Technology Reveals New Gene Ties To Autism
Study authors, led by Amy B. Wilfert, Ph.D. from the University of Washington, say new technology and dropping costs on genetic research have allowed them to gather information of thousands of genes from people with autism and their relatives. Researchers analyzed nearly 11,000 people with autism to identify the new mutations which pass from healthy;parents to children;on the autism spectrum.
The team notes most autism genes discovered to date come from research on de novo mutations. These are genetic variations that first develop in a person with autism and are not present;in their parents genes;at all. The new findings reveal that rare inherited variants which lead to autism are likely in a different batch of genes from the ones de novo mutations affect.
While most autism studies focus on de novo mutations, this study focuses on rare inherited mutations, which are often understudied in autism, says Dr. Wilfert in a;media release. We find that these variants are individually less damaging than de novo mutations but have the potential to contribute almost as much risk and impact the same molecular pathways, through a distinct set of genes. These variants, however, are only able to persist in the general population for a few generations before being selected out by evolution.
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The Role Of Rare Mutations Versus Common Polymorphisms In Asd
A series of important findings over the last four years clearly challenges the notion that autism is mainly caused by combinations of common variants by identifying a large number of rare, recurrent, and non-recurrent mutations that lead to ASD. At the same time, whole genome association studies with common variants, while identifying a few loci with very small effect sizes, have not yielded independently replicated results . These rare mutations, mostly in the form of sub-microscopic chromosomal structural variation, called copy number variants , are now known to account for up to 10% of cases of idiopathic autism . Since many of these CNV have large effect sizes and thus are thought sufficient to cause ASD, they are predicted to significantly reduce reproductive fitness. Consistent with this, these causal CNV are often not transmitted from the parent, but instead occur de novo in the germline . However, in some cases, such as CNV at 16p11 and 15q11-13, the CNV are transmitted from an unaffected parent to cause the disorder in an offspring . The genetic or epigenetic mechanism for the reduced penetrance for ASD in the mutation-carrying parent is not known. However, it is also very likely that the parent carriers of such CNV have more subtle neuropsychiatric or cognitive phenotypes that have not yet been systematically identified.
Why Is It Important To Know If You Have A Family Health History Of Autism Spectrum Disorder
Having a family health history of ASD makes you more likely to have a child with ASD, or to have ASD yourself. If you have a child with ASD, you are more likely to have another child with ASDexternal icon, especially if you have a daughter with ASD or more than one child with ASDexternal icon.;Your other family members would also be more likely to have a child with ASD.
If you are pregnant or planning a pregnancy, tell your doctor if you or your partner have a family health history;of ASD. This information can help your doctor determine how likely you are to have a child with ASD.
When collecting family health history information,
- Include your and your partners children, parents, sisters, brothers, grandparents, aunts, uncles, nieces, and nephews;
- Include anyone with a diagnosis of ASDexternal icon, learning disorder, intellectual disability, schizophreniaexternal icon, epilepsy/seizures, personality disorderexternal icon, or attention-deficit/hyperactivity disorder ;
- Note if anyone had genetic testing and the results of that testing;
- Include anyone with a genetic disorder that can cause ASD, such as fragile X syndrome or Rett syndromeexternal icon;
- Be sure to include anyone who received a diagnosis that is no longer used, such as Asperger syndrome or mental retardation; and
- Consider including older family members who have or had signs of ASD, even if they were not diagnosed with ASD, as ASD diagnoses were less common in the past and might have been missed.
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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 .
The Molecular Diversity Of Asd
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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Lack Of Sufficient Vitamin D
Less than one month ago, a new discovery was made in regards to links between Autism and pregnancy. A massive study that took place in Australia included more than 4,000 women. After analyzing the blood work of the group of pregnant women, scientists noticed an increased risk for offspring Autism in women with Vitamin D deficiencies. Women with the strongest link were those with a deficiency in that last half of the pregnancy. The research hints that low levels of Vitamin D during pregnancy could disrupt fetal brain development. The study suggests that Vitamin D supplements taken during pregnancy could significantly reduce the prevalence of Autism. Vitamin D is best known for boosting calcium levels in the blood and for promoting healthy bone and muscles growth. What most people dont know is that low levels of Vitamin D can have serious health implications. The vitamin is actually a hormone that has been long been associated with increased risk for mental health complications. For these reasons, its really not surprising that a link between Vitamin D exposure in pregnancy has been made with Autism.
What Role Do Genes Play
Twin and family studies strongly suggest that some people have a genetic predisposition to autism. Identical twin studies show that if one twin is affected, then the other will be affected between 36 to 95 percent of the time. There are a number of studies in progress to determine the specific genetic factors associated with the development of ASD. In families with one child with ASD, the risk of having a second child with the disorder also increases. Many of the genes found to be associated with autism are involved in the function of the chemical connections between brain neurons . Researchers are looking for clues about which genes contribute to increased susceptibility. In some cases, parents and other relatives of a child with ASD show mild impairments in social communication skills or engage in repetitive behaviors. Evidence also suggests that emotional disorders such as bipolar disorder and schizophrenia occur more frequently than average in the families of people with ASD.
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Prenatal Exposure To Viral And Bacterial Illnesses
You may or may not have heard this one before that getting sick during pregnancy can up the odds of an Autism diagnosis in your baby. This information has been around for quite awhile now that when infections stimulate the central nervous system of the mother, her immune response might trigger an alteration in the unborn baby. While some might assume that a more serious illness is needed, that is not necessarily true. The main causes for concern are viral infections during the first trimester, and bacterial infections in the second trimester. The highest threat arises when the mother is sick enough to be hospitalized in the 2nd or 3rd trimester. The biggest culprits are the flu, the herpes virus, congenital rubella, and borne disease. When we see rubella, we often think of the MMR vaccine and the ongoing debate over a link between Autism and the scheduled shot. Direct evidence that the vaccine could cause Autism has not been found. It is still unknown whether the risk for Rubella is still present when the mother is exposed to live vaccines.
Genetic Testing And Autism Spectrum Disorder
If your child is diagnosed with ASD, the doctor might refer your child for genetic counseling and testing.Genetic testing looks for causes of ASD but cannot be used to diagnose ASD. Some people with ASD have syndromic ASD, meaning that they have other specific features in addition to having ASD, such as looking different from other people in the family or having birth defects. Most people with syndromic ASD have a genetic cause for their ASDexternal icon.
Genetic testing is more likely to find a genetic cause for ASD if
- Your child or another family member has syndromic ASD;
- A family member has an ASD-related genetic change found through genetic testing; or
- Multiple family members have ASD.
The most commonly ordered test for people with ASD is called a chromosomal microarray . This test looks at chromosomes;to see if there are extra or missing parts that could cause ASD. CMA finds a genetic cause in 5% to 14% of people with ASDexternal icon who have the test.
In addition, children with ASD should be checked for genetic disorders that can cause ASD, including the following:
- Rett syndromeexternal icon: This disorder mainly affects females. About 4% of females with ASD have Rett syndromeexternal icon. Rett syndrome testingexternal icon should be considered for females with ASD.
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