Genetics play an important role in autism. Twin studies suggest that the heritability of autism falls in the range of 36 to 95%. Similarly striking is the fact that the risk of having a child with autism increases significantly if there is already an affected child in the family. It is therefore not surprising that approximately 10-20% of autistic children may have an identifiable genetic defect. In only a minority of these individuals, about 3%, the abnormality follows a Mendelian inheritance, i.e., a single gene is affected like in Rett syndrome or Tuberous Sclerosis Complex. In the vast majority of cases (80-85%) the genetic landscape follows a complex or multifactorial inheritance that involves both genes and environmental factors (see Figure). The question therefore arises as to when is it appropriate to refer an autistic patient for genetic evaluation?
According to a study by Schaefer and Mendelsohn, 2008) “The rationale for a clinical genetics evaluation for persons with ASDs has been questioned by some. Concerns have been expressed over the high cost of such an evaluation coupled with the fact that the information obtained typically will not change interventions for the patient. The rationale for performing a clinical genetics consultation for a patient with an ASD is clear to the clinical geneticist. Clinical geneticists can contribute to the process by examining and evaluating the patient, the parents, and siblings in order to establish an etiology. A definitive diagnosis helps the patient acquire needed services, and is helpful in many other ways for the family. Many families are greatly empowered by knowledge of the underlying cause of a relative’s disorder. Depending on the etiology, associated medical risks may be identified that lead to screening and the potential for prevention of morbidity. Specific recurrence risk counseling—beyond general multifactorial information—can be provided, and targeted testing of at risk family members can be offered. In a limited number of cases (e.g., metabolic disorders) targeted therapies may be or become available.”
I believe that all patients with medically diagnosed (as opposed to self-diagnosed) autism spectrum disorders should have a consultation with a medical geneticist, more so, if any of the following red flags are present:
Presentation of the condition: Is there an earlier age of onset or happens in the less-often affected sex (female)? Is there evidence of neurodevelopmental delay including; global speech and language, cognition, social, motor, or activities of daily living?
Family problems: Are there concerns about disease in the family? Any early disease, death or disability in the family? Are there multiple affected family members? Is there a close biological relationship between the parents (consanguinity)? Have there been problems with reproduction? Are there other risk genes or nonmedical conditions that run in the family?
Physical Examination: Is there a disorder of growth, a trend over time for short stature, somatic overgrowth, or excessive growth velocity? Are there abnormalities in the form/structure of body parts (3 or more of these may point towards a syndrome)?
Suggestive evidence of a disorder of metabolism: Does the patient complains of altered consciousness, early onset of symptoms, unusual odors, recurrent pain, unusual muscle tone, movement disorder, areflexia, decreased muscle mass, cataracts, coarse facial features, joint abnormalities, or skin/hair abnormalities?
A properly conducted genetic evaluation, usually collected from checklists, will provide valuable information to the patient and his/her family. The clinical history will be extensive including prenatal, perinatal, neonatal, infancy, childhood, and aspects of motor and social development. It will also cover the history of first, second and third degree relatives, and graphic depiction of pedigree including specific disorders relevant to presenting symptoms throughout multiple generations. For more information on the family history and pedigree aspect of genetic testing please see Saul et al., 2017.
Approximately 20% of infant deaths are due to genetic causes and 71% of pediatric-in-patients present with a significant genetic component. These conditions are extremely common, primarily so in autism where proper evaluation yield significant findings over 50% of the time. The information gained is of value for proper diagnosis, specific management, anticipatory guidance and as a means to expand our knowledge of risk factors. The high prevalence of genetic disorders in autism is an argument against neurodiversity proponents claiming autism as the result of “normal” variability in the human genome. For those interested in more information related to this subject I have written several blogs on autism-related syndromes caused by genetic defects:
Dravet Syndrome: Lessons in Regressive Autism http://bit.ly/2lurRrP
The Smith-Leml-Opitz Syndrome and Autism http://bit.ly/2m2B7Gy
Tuberous Sclerosis and Autism http://bit.ly/2lk3TP0
Ehlers-Danlos Syndrome and Autism http://bit.ly/2j5sSop
The Rare Urbach-Wiethe Disease and Autism http://bit.ly/2lPtPW6
References
Saul RA, Trotter T, Sease K, Tarini B. Survey of family history taking and genetic testing in pediatric practice. J Community Genet, 2017 (Epub ahead of print) doi: 10.117/s12687-016-0291-3.
Schaefer GB, Mendelsohn NJ. Clinical genetics evaluation in identifying the etiology of autism spectrum disorders. Genet Med 10(4):301-305, 2008.
Cortical Chauvinism 
I agree completely! For a parent, knowing about factors outside their control that may have contributed to the development of ASDs might provide some feeling of relief. From a psychological perspective, coming to terms with a chronic life altering disorder, whether it’s psychiatric, cancer, or an autoimmune disorder, there is this feeling of being out of control of the situation. As humans, especially in American culture, we feel like we should have control over our destiny and lives. I suppose that my Chilean culture shares this as well, as eloquently described by Isabel Allende. I feel like we want to blame ourselves for our diseases. «My arthritis flared up because I ate tomatoes», «My kid is headbanging because he ate gluten, I shouldn’t have let him eat pizza», «I should have bought organic strawberries, maybe I wouldn’t have cancer if I ate organic.» I lump these types of thought into the category of- If I can blame my actions , then it means it’s something I have control over my disease symptoms. You gain a feeling of control, at the expense of guilt. As humans, we seem to accept feeling of guilt more readily than feelings of being out of control. Genetics can sometimes provide answers for families that lie beyond their personal actions. For example, a Mom who had some glasses of wine before realizing she was pregnant, or who stayed on much needed antidepressant (or any other) medication during pregnancy, or who didn’t eat organic foods, or who vaccinated their child on schedule-The self-blame game kicks in. Importantly, the cost of exomic sequencing genetic services have dropped dramatically. For example, Genos.co offers exomic sequencing for $499, and genetic counseling services for $150/consultation. While I can’t vouch for the quality of their services, the reality is that we are in an era of sequencing the protein coding regions of our ALL of our genes, for less than the cost of an iPad or an iPhone. This is amazing!
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When I was 20 yo (in a previous millennium!) I spent a couple of hours harvesting strawberries in a huge wet field with not a single slug or snail anywhere to be seen. I decided something was a bit funny and never ate any non-organic strawbs ever after. I’ve since heard that non-org strawbs are some of the most pesticide-dodgy foods in the stores. I personally share 99.99% of my genes with the average slug.
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I’m not knocking an organic diet, and strawberries are on the «dirty dozen» list of having the most residual pesticides. However, without a scientific link, there is little cause to blame oneself for eating pesticide treated foods, nevertheless, people do.
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This isn’t the place to discuss pesticide dangers. There will be plenty other places discussing the evidence. Huge $billions are involved so there will be much propaganda to sort through (as with autism).
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https://www.theguardian.com/environment/2017/mar/07/un-experts-denounce-myth-pesticides-are-necessary-to-feed-the-world
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Think about expanding your thoughts and writing a blog on the subject. I would be happy to post it.
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OK, I think I could. I am more of a geneticist turned neuroscientist than a psychologist, but it is a theme/idea that I have been thinking about since my husband was diagnosed with a chronic autoimmune disorder. I started seeing similarities to the way people talk about cancer, or Autism. In addition to my Neurobiology courses, I teach a Genetics and Society course focusing on the role of genetics tests/screening,the incorporation of personalized genomics in medical decisions, and the interaction between genes and environment.
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Interesting background. As an aside there many commonalities in the risk genes for cancer and autism- but now I am going on a tangent. I am looking forwards to your contribution.
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«many commonalities in the risk genes for cancer and autism»
I have seen clear evidence (unpublished) of mercury causing cancer, and also clear evidence (my chapter 3) of mercury causing autism. Those genes that tend to retention of mercury would thus tend to increase both cancer and autism.
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Karen, I’ve just heard claims that French people are genetically less subject to harm from alcohol, which of course could be in the context of being habitual wine-oes who can’t even pronounce their own language soberly. The idea being that local population genetics has adapted to local environment. To what extent does that theme figure in your circles if at all?
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Oh Manuel! Your article was going so well until just before the end it derailed at this sentence:
«The high prevalence of genetic disorders in autism is an argument against neurodiversity proponents claiming autism as the result of “normal” variability in the human genome.»
A false dichotomy. There are specific genomic abnormalities that cause low IQ, such as trisomy 21 (Down syndrome). It doesn’t follow that therefore everyone with an IQ below my four-figure score has «low IQ disorder» rather than being just in the «normal» variance.
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I understand what you are saying and your comments are always well received. My point, if any, was that many members of the neurodiversity community won’t speak about those that are severely disabled, especially syndromic cases. It is as if they did not exist. Still in a disorder that is defined by behavioral features, you have to include them.
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I think we are equally irritated by the Neurodiversity fanatics, though at least I am not yet getting personally attacked as you yourself appear to have been!
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I also don’t enthuse too greatly about this sentence:
«Twin studies suggest that the heritability of autism falls in the range of 36 to 95%.»
Here’s a better sentence which I wrote more than 20 years ago and was published in 1993 (see printpage 220 of Chapter 7 pdf at http://www.pseudoexpertise.com ):
«If a rare perinatal adversity were to become somewhat more common, then obviously, autism of the environmental category would become more prevalent.»
And in accordance with that I suggest a better review of the twin studies is that they confirm that that change has indeed taken place, from mainly genetic back in 1977, to mainly environmental now.
By the way, I agree about the value of such testing though for an additional reason. As argued in Chapter 3 there, the evidence is firmly conclusive that most autism is nowadays caused by dental mercury and so is potentially curable by countering the mercury. But of course a Rett or TS genetic profile would suggest that mercury removal would have less hope. Though this could depend on how 100% the penetrance of the genetic condition is.
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