Home > Science > Twin Study Suggests Environmental Role in Autism: Now What?

Twin Study Suggests Environmental Role in Autism: Now What?

Posted by Alycia Halladay, PhD, director of research for environmental science, Autism Speaks

As reported last week, a large twin study supported by Autism Speaks compared the frequency with which identical and fraternal twins both share a diagnosis of autism. This approach enabled the investigators to use statistical techniques to calculate the degree to which environmental factors shared by twins contribute to their risk of developing autism. Such factors include conditions in the womb and during birth.

The results of the California Autism Twin study were game-changing because they revealed a much larger environmental influence than had previously been estimated—accounting for about 58% of the risk of developing autism. By contrast, much smaller twin studies had previously suggested that genes largely accounted  for a child’s risk of autism.

The results underscore the need to investigate the role that non-inherited risk factors play in the development of autism spectrum disorders (ASD). So what’s being done to help speed this research? And what role are Autism Speaks and its donor dollars playing in this effort?

Autism Speaks has funded over $21 million in the study of environmental risk factors, an initiative we call (obviously enough) the Environmental Factors of Autism Initiative. Already, we have a large body of evidence suggesting that it is not any one environmental factor, but many different factors working together, that elevate the risk and severity of autism in individuals with a genetic predisposition for this condition. In other words, autism is seldom caused by any one thing and neither is it an “all or nothing” condition.  Furthermore, different combinations of genetic and environmental risk factors contribute to individual cases of autism.

Within the Environmental Factors of Autism Initiative are ongoing studies focusing on environmental exposures that occur before and during pregnancy and throughout the first year of life—crucial periods for human brain development. These studies look at such possible risk factors as maternal and paternal age, socioeconomic status, season of birth, exposure to chemicals or toxic agents, nutrition and exposure to various pharmaceutical drugs during pregnancy, the difficulty of labor and delivery, and various other forms of prenatal stress.  The researchers we support are also investigating the mechanisms by which genes and the environment may interact (so-called epigenetics) and the role of the immune system.  We are also supporting large scale epidemiological studies that focus on pregnancy and the first year of life.  These include the EARLI study  and the IBIS study.

Are you interested in learning more about the studies Autism Speaks is funding with donor dollars? We are proud to debut the new Grant Search function on our website. Please use it to explore past and present research studies by topic or location. And if you or your family is affected by autism, please consider participating in one of our clinical studies.

  1. Sarah
    July 8, 2011 at 8:03 am

    YAY!!! :)

  2. Stephanie Shultz
    July 8, 2011 at 9:44 am

    Very interesting! I was wondering if there had been any study of the placenta amongst identical twins. I have 7 year old identical twin boys who had separate placentas (I was surprised to find out that if the egg splits with 72 hours you still have identical twins but separate sac’s and placentas). Both have ASD but one is more severely afflicted then the other. I have not been involved in any twin studies but would like to be!

  3. Bostonboys2
    July 8, 2011 at 10:17 am

    I have twin four year old sons, one is autistic while the other is not. What does that say? I do not think that conditions in the womb had anything to do with my autistic son’s diagnosis. Now what?

    • Mike Abramovitz
      July 10, 2011 at 8:03 am

      I’m with you! We have fraternal twin boys, 10 years old, one on the spectrum, one typical. I think we’re moving down the road and collecting data. BUT, I think the scientist need to be careful making some of these statements. There were some big sweeping statements made early on when autism was identified, blamed on the parents, the environment and people told they cannot live a life with it / institutionalized… I look at all of this as more information gathering. My son is old enough to start talking about what’s going on and why he’s not the same as the other kids. I do all this reading so I can understand a little bit more how he thinks about things vs how I do and so we can relate better to each other

  4. Lauren
    July 8, 2011 at 10:58 am

    Will autsim research also shed light on causes of Non Verbal Learning Disability?

    • flamingo
      July 10, 2011 at 3:53 pm

      One of my twins has Non Verbal Learning Disorder as well. It has a lot of the same traits as autism. I think it is confusing at some of the schools when it comes to IEP time though.

      • Lauren
        July 11, 2011 at 12:08 pm

        I can emagine. My daughter wasn’t diagnosed until college and with tutoring and help managing her daily schedule, graduated in 05.

        I haven’t been able to find that research is being done re NVLD. Since NVLD and autsim traits overlap, but it’s two distinct disorders, will austims research help shed light on NVLD? Or, does anyone know of research being done specifially for NVLD?

  5. Noreen
    July 8, 2011 at 11:06 am

    What about regressive Autism and after birth? Are there studies there? Twin studies are the way to go. It will tell so much and I don’t understand why there haven’t been more larger studies and data collected. They can help to crack some of the problem. I like Stephanie’s suggestions and also, I banked the cord blood of my ASD son and am interested in studying this. My son regresses but lucky has continued to make a lot of progress with diet, ABA and lots of PT/OT. We called in a Flu shot reaction (big inflammation that wouldn’t go down for 2 months) and the Dr. dismissed it. Also, I noted a “sensory freak out” a couple of days after my son’s 6 month shots and told my husband, “Something is just not right here”. Watching the therapy that he needed, and worked well, I often wondered about both vaccine overload causing stroke or encephalytis. I am now hearing more Dr.’s saying hold off on vaccine’s if there is a reaction. Good on them! Especially after hearing about the HPV girls and how they kept getting sicker with each shot to the point of dying, being constantly in a hospital bed or homebound for years (and they are bigger than a little baby). Glad the medical community is now “Waking Up” I hope all America wakes up to all this crap getting injected into small developing brains/bodies. I also had the flu shot when pregnant with my ASD child. He is the only one with Autism.

    • July 8, 2011 at 1:10 pm

      I agree totally on shot overload. My son was the only one to have the chicken pox vaccine among others in one day around his 1st birthday. That is when we noticed his change in personality, increased anxiety and panic. My older son and younger daughter do not have autism.

      • arahni
        July 8, 2011 at 11:35 pm

        Yes my son was teh same around 15 months with all the normal vaccinations…6, 9 and 15 months of age ones..he was fine before that…

  6. Noreen
    July 8, 2011 at 11:08 am

    After Birth is important too! : )

  7. July 8, 2011 at 11:21 am

    I have fraternal twins. My son has autism, my daughter does not.

  8. roxanne
    July 8, 2011 at 11:25 am

    I have 2 1/2 yr old twins (ferternal). One has Autism, the other does not…I also dont think the condition of the womb has anything to do with it..They both have been exposesed to the same shots, foods and enviroment conditons. Its going to be a puzzling thing for a long time unfortunatly…

    • Noreen
      July 8, 2011 at 1:08 pm

      Just for your Information, Immune systems react “randomly” No two are the same. Does your ASD child have something different (medically, allergy wise) that his other does not?? It’s just something to look at further.

  9. July 8, 2011 at 11:35 am

    I have to say I’m not sure I agree with some of these conclusions and would greatly like to see the peer review data that is available on this study and how it was conducted. I’m an identical twin, both me and my brother were diagnosed in 1993 with Asperger’s Syndrome and I was reassessed in 2006 where the original diagnosis was confirmed. My brother and I were apparently part of a study back in the 90s that helped to determine Autism is genetic and not environmental, and I am trying to also rack down the peer review data on that study as well. I’m currently working towards a Ph.D. in Clinical Psychology; this subject is of great interest to me, I’m curious to compare the data from this study & the previous study that my brother and I were subjects of.

  10. Andrea
    July 8, 2011 at 12:15 pm

    There needs to be a bigger focus on postnatal conditions and vaccinations

  11. Noreen
    July 8, 2011 at 1:04 pm

    What do the boys carry that are “stronger” genetic links? Why is so much more prevalent with Males? All people in the family of the Autistic person need to note it on their medical history and be especially observant with their children, especially the males. NOTE ANY vaccine reactions if there are any. If your child has a severe reaction to a shot, you should stop and consult a Dr. I’ve heard too many people (including nurses) state that the Dr. insisted on getting more shots and the child was hospitalized!!!! When are people going to listen???? When it’s your own son or grandson? I guess so!!! You’ll have to listen then, I’m telling you and you better have lots of cash on hand for what he direly needs in order to succeed, lots and lots of therapy!

    • Lauren F.
      July 9, 2011 at 12:42 am

      The reason boys are more affected than girls is because of genetic coding. A female genetic code includes two X sex chromosomes (XX), and boys have an X and a Y (XY). Dad always determines the sex of the baby, as the woman’s egg always produces X’s. So dad’s sperm is either an X or a Y combination, and that determines male or female. Think of a Y chromosome is an X that is missing one tail… So a female has two X’s (XX). Let’s go back to that. If part of the genetic code on one X is damaged, the other X may turn on “unused” portions of itself to “replace” the damaged or missing code. With males, the Y is essentially the X without one tail. So there are, frankly, less genes to be utilized. I have a B.A. in Psychology and this may not be the best explanation, but this is what I know. I hope it answers your question.

  12. Mae Mack
    July 8, 2011 at 1:18 pm

    My Son is now 20 years old. He has a twin sister who is not on the spectrum. Makes sense since 4 out of 5 of those affected are male. I stopped focusing on cause and looked to treatment to maintain my sanity years ago, however, now that Iwe are on the subject, I am compelled to ask the same question I asked some 15 years ago: How many of these twin/spectrum pregnancies experienced pre-term labor, subsequently treated with medications like Mag sulfate and albuterol to prolong the labor? I’ve always had a sneaking suspicion that that is the culprit. Any news on that?

    • flamingo
      July 8, 2011 at 2:37 pm

      I had identical twins in different sacks too. The doctors originally told us they were fraternal for that reason.

    • flamingo
      July 8, 2011 at 2:40 pm

      I too am very curious about the use of mag sulfate for preterm labor. I call it the drug from he**. It almost killed me literally, so I’m sure it wasn’t good for my kids either.

      • Noreen
        July 8, 2011 at 10:40 pm

        That is interesting especially since having twins ups the risks or is it Mag sulfate and albuterol? ? ?

  13. Yemina
    July 8, 2011 at 1:21 pm

    I have two year old fraternal twins. My son is Autistic my daughter is not. I am grateful that they are twins because it enabled me to see that that there was something different early on.

  14. Joe
    July 8, 2011 at 3:24 pm

    Our autism spectrum son was reared in a house nearly one hundred years old–any “domestic” issues of micro environments in the study you described? What specific environmental factors were indicated as having an impact? –chemical? airborn polutants? lead paint? What?

  15. LeAnne Cantrell
    July 8, 2011 at 3:29 pm

    Micro-preemies, babies delivered with a birth weight less than 3 pounds, have a significantly higher rate of showing signs of autism than the general population…1 out of 4. The study showing this came out a couple years ago, but is something we’ve long suspected.

    Our 10 year old boy was delivered via emergency C-section 3 months and 3 days before his due date. Cole weighed in at a wimpy little one pound, 5 ounces. After a bumpy 4 months in the NICU, we brought him home & registered him for Early Intervention services.

    I remember asking the intake people whether he could have autism or not, because instead of intently peering at my face as I fed him, Cole would gaze at the big triangular valances on his bedroom windows. Naw, they insisted….and he did grow into a very affectionate, giggly toddler with a huge vocabulary.

    When at age 2, a speech therapist mentioned PDD-NOS, I began researching preemie/autism correlations via PubMed. Studies in Japan of NICU survivors…studies out of Italy of rat pups deprived of just a smidge of oxygen…and studies of kids who had horrible jaundice all showed prenatal & postnatal risks.

    Preemie parent chat rooms also had an incredibly high role call of moms with kids on the spectrum. I bumped into parents of identical twins where the smaller twin (who presumably got less juice in utero) had full blown classic autism & the bigger twin had maybe a dusting of Aspergers

    I have long thought that moms who have multiple children on the spectrum may have antibodies which are hyper alert to the fetus; less supple endometria or placentas; or trouble absorbing vitamins & nutrients; or undetected micro-clotting tendencies.

    Autism is an obstetric and post-natal problem, and with today’s moms being encouraged to go full-bore about their lives while pregnant, no wonder these pervasive developmental delays are more prevalent amongst our kids.

    Good study!

  16. Katie Wright
    July 8, 2011 at 4:46 pm

    Dear Noreen, Unfortunately, testosterone BINDS w/ heavy metals. Estrogen protects tissue from binding w/ heavy metals. Boys just have weaker systems when it comes to tolerating multiple vaccines+ adjuvants and toxic preservatives. When I read that yrs ago I felt sick, but its true.

    Multiplex families are good but we need more research specifically on regression, adverse vaccination responses and singletons! A few yrs ago I compared some of Christian’s blood, DNA values etc w/ dozens of AGRE samples. They could not have been more different! 2 other Moms of similar regressive singletons also got the same result. We were comparing apples to oranges- like comparing aspergers to autism- 2 completely different disorders.

    Guess who results were nearly identical? All the regressive singletons! In families w/ more than I child w/ ASD the genetic cause is far stronger than w/ the majority of ASD cases, in which only 1 child is affected. Like many I stopped vaccinating my second son shortly after my first son’s dx. After a rough start, just like his brother- colic, constant reflex, screaming all the time, my second son settled right down after I stopped the vaccines. He is fine today.

    PS Aten – apergers probably has totally different origins- it is a disorder, not a disease. No one regresses in aspergers or loses all their language or becomes chronically ill. I would study aspergers specific research if I were you.

  17. Sally
    July 8, 2011 at 10:16 pm

    I have IDENTICAL twins, born in the same placenta ( I remember that specifically because they all comented on the fact that it was one placenta!) One of my twins has autism the other does not!! I have been trying to get them in studies many times with no responses. They are 10 years old and possibly hold many answers to many puzzeling questions! i would love for someone to study them!

  18. July 9, 2011 at 3:22 pm

    I have two boys, a seven year old with autism and a two and a half year old with no signs of autism. Both pregnancies were almost identical with three exceptions.
    1. With my oldest, we had a loss of oxygen scare during labor and I had morning sickness for 22 weeks. With my youngest, no scare and 40 weeks of morning sickness.
    2. Both pregnancies I was on Zofran (ondansetron) for morning sickness.
    3. My oldest was vaccinated, my youngest is NOT.

    Now, I’m really curious……???

  19. Dawn
    July 10, 2011 at 7:15 pm

    what about being on antidepressants for post partum depression while breastfeeding???

  20. July 14, 2011 at 9:53 am

    Environmental causes have always been what my heart has told me to be the reasoning behind the tremendous increase in autism. Naturally, the EPA has always assured us that our environment is perfectly safe, the movement for a cause has always been to look at genetics, the broadening of the diagnosis spectrum, immunizations, etc…One theorist even considered this to be an evolutionary event due to the techno-era.
    It really doesn’t matter if you call it autism or anything else, the fact is, we would have to call it something because our children are physiologically different from what we consider “normal” people.
    Finally, we are seeing studies that are linking the environment to the spike in autism. The first correlation I learned about was the proximity to freeways which share a commonality. Frankly, I never thought I would see the day that anything else would surface.
    I am so relieved to see this article!

  1. September 30, 2011 at 5:06 am

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