Ex Derdrie Imus Environmental Center for Pediatric Oncology team leader Philip J. Landrigan is the latest scientist once associated with the debunked vaccine causation ideas to repudiate those ideas in a scientific journal.
Writing in Current Opinion in Pediatrics, Landrigan has published ‘what causes autism? Exploring the environmental contribution’ in which he explores what might be a plausible environmental causation. He also touches on genetics and the so-called ‘autism epidemic’.
Touching on genetics, he states:
Genetic and familial factors are unquestionably involved in causation of autism [4]. Families with multiple cases have been described. Autism has repeatedly been seen in sibs and twin pairs. Concordance in monozygotic twins is
reported to be as high as 70% [15], and, when the broader phenotype of autism is considered, concordance in monozygotic
twins approaches 90%. Concordance rates for autism in dizygotic twins appear no higher than among singleton siblings. Families with autistic children may contain members with ‘autistic traits’ such as social isolation or tendency toward repetitive behavior [13]. Autism occurs in a number of genetic conditions, among them Fragile X syndrome, Down syndrome, Cohen syndrome, Angelman syndrome [16] and Rett syndrome [17].
Regarding genetics as a whole Landrigan claims that autism can already be accounted for to the tune of between 7 – 8%. In an email to me he stated:
THE FRACTION OF AUTISM CASES THAT CAN RELIABLY BE ATTRIBUTED TO GENETIC CAUSES WILL CERTAINLY INCREASE AS MORE RESEARCH COMES IN
By how much though? No idea and Landrigan wouldn’t be drawn.
Regarding the ‘epidemic’ Landrigan states:
The reported increase in prevalence of autism has triggered vigorous debate as to whether the trend reflects a true increase in incidence, or is merely a consequence of expansion in the definition of ASD and greater awareness, improved diagnosis and better reporting [11]. This highly controversial question is not yet settled [14]. A
recent critical analysis concludes that increases in recognition, changed diagnostic criteria, and changing public
attitudes about autism have played a major role in catalyzing the upward trend in reported prevalence. This analysis observes, however, that the possibility of a true rise in incidence cannot be excluded [12].
Which should be – if one is truly interested in following the science so far – the correct conclusion. In other words, nobody really knows but the recent increases in recognition, changed diagnostic criteria and changing public attitudes (amongst other things) have played a major role.
In relation to vaccines, Landrigan states unequivocally that:
To address the issue, a series of studies was undertaken in the US, the UK, Europe and Japan. None of these studies have found any credible evidence for a link between vaccines and autism [12]…..Fear of autism does not justify failure to vaccinate children against life-threatening diseases [75].
In an email to me Landrigan stated:
IT WAS RESEARCH THAT NEEDED TO BE DONE. BUT NOW THAT WE HAVE MORE THAN DOZEN, HIGH-QUALITY NEGATIVE STUDIES OF THE ISSUE IT IS TIME TO MOVE ON…
I’m not sure it was research that needed to be done given the extremely tenuous hypotheses that began the various vaccine/autism strands but I agree that it is time to move on.
I was somewhat surprised at this paper as I had become used to seeing Landrigan’s name associated with those who believe vaccines cause autism and certainly his involvement with Derdrie Imus would indicate his belief in that set of ideas. It was a nice surprise to see that he was sticking to the science.
So what can we draw from this? First and foremost we have to say that a colleague of Derdrie Imus stating publicly that vaccines don’t cause autism is the biggest red flag so far that even the scientists who once gave credence to those ideas are moving away from them. Secondly we can say that althoough we cannot preclude the idea of a real actual increase, the major role in causing an increase in autism numbers still remains the combination of increased recognition, changed diagnostic criteria, changed public attitude, diagnostic substitution, more available locations for gaining a diagnosis and more doctors trained to give diagnoses. Lastly we can say that here is a toxicologist who acknowledges that there is a strong genetic component and that that component is likely to increase.
Left Brain Right Brain 
This can only mean one thing – that Dierdre Imus has PHARMA ties!!!
Kev,
It is truly amazing that you take a piece that says, as the summary –
“Expanded research is needed into environmental causation of autism. Children today are surrounded by thousands of synthetic chemicals. Two hundred of them are neurotoxic in adult humans, and 1000 more in laboratory models. Yet fewer than 20% of high-volume chemicals have been tested for neurodevelopmental toxicity. I propose a targeted discovery strategy focused on suspect chemicals, which combines expanded toxicological screening, neurobiological research and prospective epidemiological studies”
And try to spin it into a autism is genetic and we are just better at seeing it story. The paper may have some quotes which you clearly are mining but the summary clearly contradicts what you are saying.
If chemicals in the environment are responsible for autism then it it highly unlikely that the rise in the rates of autism are primarily due to social factors.
I have to admire the little jihad you have going against the idea that autism is becoming more common but you really might want to come back to reality one of these days.
Its truly amazing that you think more detail can be gained from the summary rather than the main body of the paper MJ 🙂
I spoke with the author and quoted his exact words concerning subjects that interested me – you on the other hand have read what you want into a bare bones summary. Good luck with that.
That’s simply untrue. To take an example, think lead.
Hello friends –
Funny stuff.
The paper is clearly, quite clearly written to discuss environmental impacts; just check the title! You can find the same boilerplate quotes concerning the heritability of autism in pretty much any paper you pick up on autism. The fact that you were able to strip out a single quote from some unknown number of emails about ‘something of interest to you’ is of little concern about drawing conclusions about what the author really thinks, but may make you a job candidate for the Chicago Tribune.
Unfortunately, the fact that things happen more similarly to twins doesn’t necessarily mean that it is the result of genetics. What’s more, some of the synthetic chemicals our infants and neonates are swimming in have been shown to have a variety of disturbing effects; the exact thing that the author seems to have written a paper about.
Based on a discussion I was having on this site a few days ago I ran into this paper:
Prenatal Exposure to Organohalogens, Including Brominated Flame Retardants, Influences Motor, Cognitive, and Behavioral Performance at School Age (full paper)
The full paper goes into much more terrifying detail. For a review of what is (currently) known about the developmental neurotoxicity of this class of chemicals, this paper is pretty good. (and terrifying)
DEVELOPMENTAL NEUROTOXICITY OF POLYBROMINATED DIPHENYL ETHER (PBDE) FLAME RETARDANTS
We can not and should not let a hyper focus on vaccines dissuade us from the very real possibility that our incredibly reckless distribution of synthetic chemicals into the environment isn’t having an effect on our infants. Landrigan is right.
– pD
pD – I write about what interests me 🙂 I don’t think I’m denying what the author is saying elsewhere but as to what interests me, I’m interested in what he has to say as someone who used to work with a keen proponent of the autism/vaccine ideas.
If you want to discuss what interests you, why not start your own blog?
I’ll bite. What explains, in your view, the difference in concordance between MZ twins and DZ twins or siblings, pD?
pD opines:
That’s true if there is no difference between fraternal (dizygotic) twins and identical (monozygotic) twins. However, if identical twins (who are genetically identical) have these “things” in common more often than fraternal twins (who are no more genetically related than any siblings), then there is a genetic component.
Autism has been shown – repeatedly – to be significantly more concordant with identical twins than fraternal twins. A number of people have tried to spin this as a “genetic predisposition triggered by an environmental exposure”, but it’s a hard thing to spin that way. Maybe if we were looking at twins separated at birth, who had significantly different environmental exposures, then it might make sense. But twins generally have near identical environmental exposures.
Prometheus
Is testosterone exposure in the womb, an Environmental factor?
Is Valproic acid exposure in the womb, an Environmental factor?
I’m confused.
Kev, you said –
“quoted his exact words concerning subjects that interested me”
Hence why I said you went for specific lines but ignored the entire topic of the paper. Anyone can take a few lines out of context and use them to prove their points.
Joseph you said –
“That’s simply untrue. To take an example, think lead.”
Perhaps I should have been clearer. But social factors I meant to refer to the criteria that Kev was using such as increased recognition, etc.
Lead is not a social factor – it is a chemical substance that is in the environment. The emission of lead may be socially influenced but that is not the social factors that Kev was talking about.
“I’ll bite. What explains, in your view, the difference in concordance between MZ twins and DZ twins or siblings”
Per the CDC (and other recent papers)-
http://www.cdc.gov/ncbddd/autism/research.html
Among identical twins, if one child has an ASD, then the other will be affected about 60-96% of the time.
In non-identical twins, if one child has an ASD, then the other is affected about 0-24% of the time.
Parents who have a child with an ASD have a 2%–8% chance of having a second child who is also affected.
Or in other words, DZ twins both have autism more often the normal siblings and MZ twins don’t always both have autism. If a set of MZ twins don’t both have autism then the cause of the autism isn’t genetic but almost has to be some sort of environmental factor.
Promethus you said –
“However, if identical twins (who are genetically identical) have these “things” in common more often than fraternal twins (who are no more genetically related than any siblings), then there is a genetic component”
Then what does it mean when autism is more common in DZ (especially male-male) twins than normal siblings? DZ twins are no closer genetically than normal siblings but do share more of their environment. The most recent paper that I read on the topic showed about a 40% concordance for male-male DZ twins and about 86% for male-male MZ twins.
Again, as I pointed out to pD –
1) I blog what interests me – you have a blog, use it to talk about what interests you 🙂
2) The keywords for this paper include ‘vaccines’ , hence I partly talk about vaccines.
I’m not trying to hide what the paper is about, I’m just discussing certain aspects of it. Maybe when I’ve talked more with the author I’ll talk about the rest. Maybe I won’t.
Socrates,
I would say yes to both. Whether they are proven to be linked to autism is a separate question.
There are multiple environmental factors that are linked to autism. Most if not all are prenatal. The most striking example is rubella infection. Children born with Congenital Rubella Syndrome are much more likely to be diagnosed with autism. There are big spikes in the number of clients of the California Department of Developmental Services with autism for birth years during the rubella outbreaks of the 1960’s.
I believe Patricia Rodier went into some detail about the known possible environmental factors during the autism omnibus. Again, the environmental factors were prenatal.
Hello friends –
I’m not here to deny a genetic component to autism, but the lightning fast gunslinging of twin studies hinges on the notion that there is only one way to get to a particular developmental endpoint – genes. If we accept that there are other ways to achieve a particular developmental endpoint, a reliance on twin studies shows itself as a fallacy. You can have genetic and environmental mechanisms affecting neurodevelopment if we allow ourselves to believe that autism rates are increasing, but you can’t have the opposite; to believe that autism rates are stable, we can’t allow any intrusion of changes to our environment to be affecting neurodevelopment.
Of course, when pressed, say with studies involving something like valporic acid, as mentioned by Socrates, and a whopping increased risk, you can get the acknowledgement that there are some things that can cause autism that aren’t genes, quickly followed by the impossible to substantiate claim that the amount of increase is very minor. Unfortunately, we need to start ignoring mounting reams of clinical evidence from a galaxy of sythentic chemicals for this to make any sense.
Take the study I posted above, Prenatal Exposure to Organohalogens, Including Brominated Flame Retardants, Influences Motor, Cognitive, and Behavioral Performance at School Age, which, curiously, got left out of any discussions so that we could discuss twin studies.
To illucidate briefly the frailty of an argument exhonnerating our influx of chemicals into the environment, lets examine one of the proposed mechanisms by which organohalogens are believed to affect neurodevelopment; affecting thyroid metabolism.
There are a number of studies showing the ability of a wide range of chemicals to modify thyroid metabolism, here, here, or here.
Having thyroid metabolism interferred with during pregnancy is associated with a variety of bad outcomes, inclding, Pervasive developmental disorders, autism, reduced cognitive abilities , ADHD and many, many other condtions.
Unsurprizingly, when we look for associations between levels of these chemicals and development outcomes, we find results that should surprise no one, such as the study I linked to above, or another, here.
The facts on the ground are that these chemicals are completely novel to our planet in the past few decade and many have reached environmental ubiquity. We have a growing understanding of the mechanism(s) by which these chemicals can affect developing brains, and association studies that indicate that our clinical observations have merit for a variety of conditions, including autism. Finally, we seem to be observing an explosion of ever increasing behavior patterns that no one can really explain without necessarily invoking an the ever hopeful idea of progressing decrease in uncertainty of our diagnostic as rates continue to go in a single direction.
The fact that twins have autism more frequently does absolutely nothing to change any of this if we allow ourselves to believe our observances of increase are not completely an artifact; but the inverse does not hold true. We must find a reason to believe that all of these studies, and many, many others are all wrong in exactly the same way for our environmental engineering to be without consequence.
– pD
pD may take this opportunity to bring us up to date on monochorionic vs. dichorionic twinning studies and the possible effects of a shared intrauterine environment.
There may well be room for prenatal environmental factors in ASD—there just doesn’t seem to be much room.
Joseph (http://autismnaturalvariation.blogspot.com/) pointed out that the data in the Hertz-Picciotto and Delwiche study [Epidemiology. 2009 Jan;20(1):84-90] that is sometimes touted as indicating environmental effects (well, at least Hertz-Piccioto’s rather exuberant press conference is sometimes quoted) actually indicatea that 62% of the apparent increase in ASD is due to the four factors affecting diagnosis that they investigated. King and Berman [Int J Epidemiol. 2009 Oct;38(5):1224-34] (who, like Hertz-Picciotto and Delwiche, used data from the California Department of Developmental Services) suggested that 26% of the increase in ASD captured in the was associated with a fifth factor: assigning an ASD diagnosis to individuals previously identified as mentally retarded. Thus, although neither paper analyzed the effect of increased awareness—something difficult to measure, but perhaps a major factor contributing to the observed increase—it does seem as if changes in diagnostic practice contribute to the observed increase, even if they do not explain ALL of it.
Eric Fombonne’s 2008 statement [Br J Psychiatry. 2008 Jul;193(1):59] still seems reasonable: “Changing diagnostic criteria, broadening of the autism concept, diagnostic substitution (from ‘mental retardation’ to autism), improved services and awareness all contributed. Autism has a strong genetic basis but the possibility of additional causal environmental risk factors remains. The neuropathology and neurobiology point towards prenatal abnormal brain development. If environmental risks contribute to the increase in incidence, their impact must occur at or shortly after conception but no solid clues are yet available.” Michael Rutter, in his comment on King and Bearman, noted that one “environmental factor” is apparently increasing parental age, which increases risk of ASD; exposure to prenatal toxins or infections may be important in explaining some of the remaining minor portion of the apparent increase that is not associated with diagnostic changes or the increase in parental age.
It’s notable that Landrigan has backed away from the “vaccines-cause-autism” notion, since that seems to have lost essentially all of its support if not yet all of its supporters.
Sorry–I meant my comment above to read: “There may well be room for prenatal environmental factors in IN THE APPARENT INCREASE IN ASD—there just doesn’t seem to be much room.”
The genetics of autism has been investigated pretty well. Except for the few single gene causes, the genetics are virtually completely opaque. The single gene causes added all together represent about 15%, but the statistics are bad because none of them are more than a few %.
The single gene causes are mostly sporadic. It is the familial autism cases that have the most complex genetics. In the type of autism that runs in families, no gene contributes more than a few % to the phenotype. This has been shown very well by full genome scans of thousands of individuals.
The incidence of autism in monozygous twins is higher than in fraternal twins, and the incidence in fraternal twins is higher than in full siblings. My interpretation is that the in utero environment is important. Both types of twins share an in utero environment. That environment isn’t identical, even for monochorionic twins. Development is chaotic, it exhibits the “butterfly effect”. Differential changes early on (i.e. in the first trimester when autism happens) can have macroscopic effects observable only later. Monochorionic twins can be discordant for anencephaly. That isn’t “genetic”, it is bad luck from the in utero environment.
It is in the first trimester that thalidomide causes autism, that valproate causes autism and when the number of minicolumns is fixed. Increased exposure to stress in utero increases the incidence of autism. Exposure to cigarette smoke decreases it. Exposure to birth control hormones decreases it. Everything that is known to be associated with autism is consistent with low nitric oxide.
When there have been industrial exposures to halogenated compounds, there has not been an increase in autism. The cooking oil contaminated with PCBs didn’t increase autism or have symptoms similar to autism.
There has been autism in pre-industrial times. I think that children with autism were the children thought to be “changelings”, where a human child was thought to be exchanged for a non-human. I think that parents who thought their child was a changeling were the medieval equivalent of curebies. They felt such hatred toward their child, their only explanation was that fairies had substituted a non-human child. Hate the child, hate autism, hate the pharmaceutical companies, hate the fairies.
Hi brian –
RAJ is likely more well suited for that task.
Now that you mention it, however, our existing evidence points strongly towards an effect in the amniotic environment; well, if you insist on the strength of twin studies anyways. For example, the concordance of DZ twins is around thirty percent, but the concordance of siblings hovers far, far less than that, around 10%. What can we glean about the uterine contribution, as compared to the genetic contribution from this information? Do we have some evidence that DZ twins are more genetically similar than sibilings? If we do not have such evidence, what does this tell us? Why would we observe such a large difference in the rates between siblings and non identical twins? This is a genuine question.
I am not arguring against a contribution of diagnostic practices contributing to an observed increase. I am arguing that, as I practice it, a precautionary principle regarding our observed increase mandates that evidence from a variety of clinical and association studies merits grave concern over the impact of our reckless introduction of a variety of things into our infants environment that was simply not in existence several decades ago. Those same chemicals, in vitro have shown wide ranging ability to affect reactions involved in neurodevelopment.
When politically expedient, the California data set is raked over the coals as difficult to assign certainty to and full of inaccuracies. Who would have guesed that it depends on which argument is being made?
In any case, my arguements are completely independent of those of Hertz-Picciotto; we have plenty of evidence from sources far less fuzzy that figuring out what percentage of drift arises from “greater awareness” that our chemical environment is different, and worse, for this generation of infants than generations past.
If I were to ask you to quantify in a more meaningful fashion than much room for an actual increase, your response would not only contain no values we could test against, they would hinge on studies using the same vilified data set and biases as HP, it would also necessarily rely on the types of studies that have been notoriously unreliable in the past, except that they continue to show the same trend over time, upwards.
Likewise, if I were to ask you what amount of much room should qualify as an emergent health crisis, as opposed to a reason to put our faith into studies based on data that is accepted as poor quality when the situation fits, what would your answer be?
No it isn’t.
– pD
Hi pD – ‘no it isn’t’ – funny stuff 🙂
It actually is you see. If you take a quick glance at the listed keywords for the paper one of them is ‘vaccines’.
With all the theories about the cause and cure of autism that are being bounced around I am surprised no one has ascribed cause to nomenclature. An overview of autism writing shows a disproportionate number of autistic kids with the names Josh, Luke, Alex and Brandon thus suggesting possibly a numerological cause. Needless to say that this is largely anecdotal and based on a very limited sample but I think my level of rigour acceptable in this debate. I would have suggested a divine cause but we have left such superstitions behind, have we not?!
Diagnostic substitution is a politically correct label for misdiagnosis. Moss and Howlin recently published a paper on the association between genetic syndromes (Fragile X, Rhetts, Tuberous Sclerosis, Downs, Angelman syndrome among others). They found that the association between the genetic syndromes and ASD is superficial.
http://www.ncbi.nlm.nih.gov/pubmed/19708861?
Kanner in his early writings suggests that this is not a new problem. Kanner in 1965 wrote:
“Moreover, it became a habit to dilute the original concept of infantile autism by diagnosing it in many disparate conditions which show one or another isolated symptom found as a part feature of the overall syndrome. Almost overnight, the country seemed to be populated by a multitude of autistic children, and somehow this trend became noticeable overseas as well. Mentally defective children who displayed bizarre behavior were promptly labeled autistic”
http://neurodiversity.com/library_kanner_1965.html
Child Psychiatry has never been able to control for cognitive impairment and the severity of cognitive impairment. One example is the association between Angelman Syndrome and ASD. While ASD researchers have included Angelman Syndrome as one of the genetic syndromes associated with autism, the families and researchers who joined in a collaborative effort to understand the genetic basis for Angelman and research to develop treatments have stated unequivically that Angelman Syndrome is often misdiagnosed as cerebral palsy or autism:
http://www.angelman.org/stay-informed/
In 1999 Rutter published papers(s) on the association between Romanian orphans abandoned at birth and placed in horrific institutions. Rutter compared the outcomes between Romanian orphans who experienced severe emotional deprivation and English born orphans also adopted into well functioning English families. 9.2% of the Romanian orphans were diagnosed with an ASD using ‘Gold Standard’ diagnostic tools. While their were similarities between the Romanian orphans and ordinary autism, the differences suggested a different meaning. Rutter coined the term ‘Quasi-Autism’ to describe these children.
Kanner also reported a similar phenomena that occured in the 1950’s:
“To complicate things further, Crewel, in the hope of avoiding confusion between true autism and other conditions with autistic-like features, suggested the term pseudo-autism for the latter. Even this term came to be employed haphazardly, and conditions variously described as hospitalism, anaclitic depression, and separation anxiety were put under the heading of pseudo-autism”
The AGRE database has coined a term for subjects who did not meet cutoff points for an ASD diagnosis using another ‘Gold Standard’ diagnaostic tool. They labelled the subjects NQA (Not Quite Autism).
Cutoff points which record a growing number of isolated symptoms that are shared in numerous neurodevelopmental and neuropsychiatric conditions(including adult stroke patients)are abitrary. If you have X number of symptoms you are autistic, if you score one point below the arbitrary cutoff you don’t have it.
Diagnostic substitution, or more succinctly misdiagnosis, explains virtually the entire so-called ‘autism epidemic’.
The critical year that marked the beginning of the autism epidemic is 1994 which coincides with the publication of DSM-IV (1994) and ICD-10 (1994). That was the year when Kanners core defining feature ‘A pervasive lack of responsiveness to other people – autism’ (DSM-III 1980) was completely removed from all diagnostic schemes including the Gold Standard diagnostic tools (ADOS, ARI) and was replaced by the vague, ambigous and subjective ‘Qualitiative impairment is social interaction’.
http://www.unstrange.com/dsm1.html
Prometheus
What factors cause differences in the genetic make up of monozygotic twins. Copy number variations would certainly be one. What many people want to know is why the concordance in MZ
twins is not 100%.
I told you Sid, until you can answer questions you’re not welcome here.
One thing which puzzles me about the diagnostic substitution argument concerning those with MR, is the ratio of children with autism are IQ scores below 70 has reversed in recent years. In the past, If I recall correctly about 2/3 of those with autism had IQ scores below 70, but now 2/3 of those with the condition have IQ scores > 70.
If autism numbers are growing due to the inclusion of those who have MR, then why has the ratio flipped.
As I’ve pointed out (to you included, MJ) many times, you’re expecting autism to meet an impossible genetic standard. There’s basically nothing in humans that has 100% MZ concordance and low DZ concordance.
That’s not to say that there aren’t environmental factors associated with autism. There can be, and some are pretty well accepted to exist. But this “concordance is not 100%” argument is not a good argument to show that an “environmental factor” is causing autism.
Obviously because there’s increasing recognition of autism in the population with MR, but also in the population without MR. In fact, the population without MR is much bigger, and it’s not surprising there’s more room for recognition growth in this population.
In CalDDS, this is pretty clear over time. I’ve even modeled this (i.e. prevalence vs. proportion of autistics with MR) and the fit of a power model is nearly perfect.
This can also be observed across regional centers, but it’s not as clear. That is, regional centers with higher administrative prevalence tend to have a lower prevalence of MR in the autistic population.
It is interesting to note that in IDEA not a whole lot of autistics should be coming from the MR category. In Shattuck’s model, keep in mind that he also looked at SLD. Other categories are relevant as well. It could be a pretty complicated pattern.
Ian you said –
“What factors cause differences in the genetic make up of monozygotic twins. Copy number variations would certainly be one.”
It is my understanding the MZ twins will share copy number variations as well as most other common genetic variations. The only time that isn’t true is when a prenatal or postnatal exposure causes a mutation – ie the environment.
“As I’ve pointed out (to you included, MJ) many times, you’re expecting autism to meet an impossible genetic standard. There’s basically nothing in humans that has 100% MZ concordance and low DZ concordance.”
And as I have pointed out to you, that argument simply isn’t true.
Anything that is strictly genetic – for example hair or eye color – will be the same in basically every set of MZ twins. Things that aren’t – such as handedness (80%) – show a strong correlation between MZ the twins but DZ twins are no more concordant that other siblings.
With autism you have MZ (90%) > DZ (30%) > siblings (8%).
It isn’t just that MZ twins have a high concordance and DZ twins are lower. Rather it is MZ is lower than it should be for something that is strictly genetic and DZ is higher normal siblings. DZ twins are no more genetically alike than ordinary siblings but they do share the same prenatal environment and (depending on the family) the same childhood environment.
Both of these facts point to a larger role for environment influences.
Try spending some time around MZ and DZ twins and you will get a better understanding of what I am talking about.
Joseph. I accept that more and more people who do not have MR are being diagnosed as autistic. I’m arguing against the reclassification of those who have MR to autistic as the primary cause. It could be contributory, but it cannot be the primary cause.
Fascinating to hear any head way scientifically.
I think this is a great website by the way. I’ve linked to it in my blog Bob Versus Autism where I ask whether it’s ALL bad:
http://bobversus.com/archives/501
Have a Kim (Peek, get it?)
The autism twin studies have all used the classical design method. For a condition whose etiology is not known classical twin study design cannot distinguish genetic transmission from genetic susceptability.
The cause of leprosy is infection after exposure to myobacterium leprae. Twin studies in leprosy have reportd the same high (60-85%) concordance rates in in MZ twins and the same rapid falloff in concordance rates (5-20%) in DZ twins that has been reported in autism twin studies.
http://www.ncbi.nlm.nih.gov/pubmed/11279529
Twin researchers have tried to use mathemematical calculations to control for chorion effect to publish heritability estimates for different conditions. Moore, using a sib-sib multifactorial hypothesis managed to calculate an 80% heritability estimate for leprosy.
http://www.springerlink.com/content/q4wr6168g1j16386/
While no autism twin studies have seperated concordance rates by chorion type for same ASD diagnosis, a number of twin studies related to various lines of ASD research have. Sokol et al who found MZ/MC twins to be more alike in terms of personality development than MZ/DC twins. Genetics cannot explain the difference since all the twins were MZ. Similar results were found with respect to IQ differences, brain development (Corpus Collosum) differences, even X-inactivation in female MZ/DC twins compared to MZ/MZ female twins.
All the studies reported that MZ/MC twins are more alike than MZ/DC twins which suggests the importance of the prenatal environment and the risk for gene-environment interactions playing an important role in development.
The California Autism Twin Study (CATS) study has closed its recruitment phase, CATS has recorded chorion type where the information is available. If, and its a big if, they have a large enough sample of MZ twins with accurate chorion data, this may be the most important study published in several decades and may finally answer the question of whether autism is primarily a genetic defect or is primarily the consequence of gene-environment interactions.
We won’t have to wait long. The recruitment phase is completed, the data is being sifted through and analyzed. I expct the results will be published later this year. Lets hope they have recruited a large enough sample of MZ twins with unambigous chorion data to give an answer to the question that has never been resolved: “Is autism a strongly genetic disorder”?
This is not exactly true. I believe MZ concordance of eye color is about 98%. And DZ concordance is about 50%. I said 100% MZ concordance and low DZ concordance.
Either way, it’s ridiculous to compare a straightforward physical characteristic such as eye color to a behavioral phenotype like autism. You need to find something like personality or intelligence, having 100% MZ concordance, to even begin to have an argument.
The standard explanation for discordance in genetic syndromes like Fragile X or Down Syndrome appears to be epigenetics. I’d also suggest it’s reasonable to suppose that human development is, to a certain extent, chaotic.
I would be interested in seeing how non-autistic MZ twins of a autistic MZ twin fair in terms of presenting with autistic traits.
Is there any indication in the studies indicated in the OP as to just how close to the cut-off (of whichever ax was used) the non-autistic twins generally were?