Sunday, July 17, 2011

Got Twin Studies?

In light of the recent study showing that the concordance of autism in twins might not be what we think it is, I was going back and looking at historical twin studies.  Specifically, I am looking for older studies that -
  1. Compared identical (MZ) twins to fraternal (DZ) twins. 
  2. Compared the concordance of actual autism diagnoses using an established diagnostic test.
  3. Had some way of determining which twins were identical or fraternal without having to resort to estimates.
There are plenty of studies that compare "autistic traits" in twins (I found at least 11 of these) but surprising few that look like they would meet the criteria above.  So far I have found these - 
  • Folstein, S, and M Rutter. 1977. “Infantile autism: a genetic study of 21 twin pairs.” Journal of child psychology and psychiatry, and allied disciplines 18:297-321. 
  • Ritvo, ER, B J Freeman, A Mason-Brothers, A Mo, and AM Ritvo. 1985. “Concordance for the syndrome of autism in 40 pairs of afflicted twins.” The American journal of psychiatry 142:74-7. 
  • Steffenburg, S et al. 1989. “A twin study of autism in Denmark, Finland, Iceland, Norway and Sweden.” Journal of child psychology and psychiatry, and allied disciplines 30:405-16.
  • Bailey, A et al. 1995. “Autism as a strongly genetic disorder: evidence from a British twin study.” Psychological medicine 25:63-77.
  • Kees, E.K., Hefter, R.L., Klaver, J., Schweigert, S.A., Arneson, C., Gernsbacher, M.A., & Goldsmith, H.H. (2005, June). Twin concordance for the autism spectrum based on community diagnoses and screening of a birth cohort. Behavior Genetics, 35, 809. (abstract)
  • Taniai, Hiroko, Takeshi Nishiyama, Taishi Miyachi, Masayuki Imaeda, and Satoshi Sumi. 2008. “Genetic influences on the broad spectrum of autism: study of proband-ascertained twins.” American journal of medical genetics. Part B, Neuropsychiatric genetics : the official publication of the International Society of Psychiatric Genetics 147B:844-9. 
  • Schweigert,E. K., Gernsbacher,M. A., Hefter,R. L., Gottesman, I. I., Goldsmith, H. H.  (2009, May).  Twin Concordance for Autism: a Comparison of Multiple Diagnostic Criteria in a Population-Based Twin Study.  INSAR Poster.
  • Rosenberg, Rebecca E et al. 2009. “Characteristics and concordance of autism spectrum disorders among 277 twin pairs.” Archives of pediatrics & adolescent medicine 163:907-14.
  • Hallmayer, Joachim et al. 2011. “Genetic Heritability and Shared Environmental Factors Among Twin Pairs With Autism.” Archives of general psychiatry 1-8. (Accessed July 10, 2011).
Does anyone know of any others?


  1. Hi MJ -

    Not sure how well these fit your criteria, but I ran into these a while ago when I was investigating the data on whether the process of 'twinning' was a risk factor for autism in itself.

    Excess of Twins among Affected Sibling Pairs with Autism: Implications for the Etiology of Autism

    Increased Rate of Twins among Affected Sibling Pairs with Autism


    - pD

  2. Thanks pD, I will take a look at those.

    Just out of curiosity, did you ever form an opinion as to whether the twinning process - either MZ or DZ - contributed to the risk of autism?

  3. Hi MJ -

    I was torn, I really liked the underlying biological plausibility, being a twin involves more stress on the mother, and likely, uneven and reduced distribution of nutrients. This seemed to fit well with the idea that gestational disturbances could alter brain development.

    However, there were some larger studies that seemed not to find an effect. I did not include these here, as they did not perform diagnostics, but rather, relied on phone survey information.

    I guess I came away wishing I could make sense of the mess. At least I got a familiar feeling out of it. It wouldn't surprise me if there was a subtle push towards autism, but I don't think we can detect it with our studies currently available. (?)

    - pD

  4. Hi MJ -

    Serendipity strikes again. Published today:

    No major effect of twinning on autistic traits.

    Note that they did find an effect, just found it to be 'not major'. Also, this was a Baron-Cohen thing where they tested out yet another questionairre for determining 'autistic traits'.

    To my mind, not really good evidence, but you seem more capable with the statistical stuff than me.

    It does look like a question that people are opening asking again, and thats a good thing.

  5. Hi pD,

    Thanks for the study from today, it looks like a confusing result though. If I am reading it correctly, it looks twins are less at risk for autism - or more appropriately more likely to score lower on the CAST.

    Although I have to say that SBC's studies always seem to make me twitch. From his insistence on calling the autism spectrum "autism spectrum condition" to his obsession with testosterone to his continued use of these random screens that don't have much testing outside of his group. I am not sure that he does much besides muddy the waters.

    I am a little surprised that twins haven't been consistently shown to be at a higher risk for autism. With all of the extra prenatal complications, the extra stress on the mother's body, and the far greater chance of being both premature and at a low birth weight, I would have thought that there would be an easily measurable risk there. That isn't even taking into account all of the twins that are born because of fertility treatments - in my experience, fertility treatments seem to account for almost half of the DZ twin population.

    Maybe the answer is that twins are more social from birth? They have a built-in peer their own age who they can practice their social skills with? I know that my twins were starting to team up and act as a pair before they had their minor regression and lost that ability. But even after that, they seem to be very close to each other and in tune with their twin's needs - far more so than they are with any other person.