Austism Twin Study: Searching for the Cause of Autism and the Perfect Sandal

  Does the environment plays a bigger role in triggering autism than we thought? 




CORK SANDAL by Jessica Simpson

 

Could this study be a summer trend like those cork sandals from the 1970s.  In other words, a dramatic tease ultimately shoved to the back of the epidemiological closet?

Here’s the low down:

Researchers (partially funded by Autism Speaks) gathered 192 sets of twins (identical and fraternal) in which at least one twin had been diagnosed with an autism spectrum disorder.  Now because identical twins share 100% of the same genes (at least at the start) and fraternal, about 50% respectively (as do non-twin sibs), these kids offer a ready-made study of the relative contributions of genes versus the environment. 

The greater the predicted role of genes, the more we’d expect higher concordance rates among identical twins (i.e. if one twin has autism, the percentage of cases in which the other twin does too).  Hypothetically if genes were solely responsible than if one twin had autism, the other one would too, guaranteed – a concordance rate of 100%.  Non-twins sibs and fraternal twins would be roughly equal and considerably less that the identical rate as both groups share the same amount of DNA (roughly 50%). 

The curious part is explaining different concordance rates between the groups when environmental triggers appear on the scene (as they surely do with autism) especially during the prenatal period.  Because twins share the womb, we’d expect the concordance rates to be closer together for identical and fraternal twins if in fact there are prenatal environmental triggers.  Hypothetically if there were no genetic component, we’d expect the rates to look similar for identical and fraternal twins.      

But back to reality… 

The researchers found when one identical male twin had autism, the other did too in 77% of the pairs. The “concordance” among identical girls was 50%.  As for the fraternal twins, if one twin had autism, 36% of girls and 31% of boys did too. 

Okay, nothing so unusual thus far.  Those figures are somewhat in line with rates in recent studies though some have calculated it around 90% for identical and 10% for fraternal.  If anything the fraternal rate was considerably higher than past estimates as some studies put it at about zero though many have doubted it was really that low. 

But it was what the research team did next that raised some eyebrows.  Using high-powered new statistical techniques that confuse most people they estimated the portions of autism triggered by both  environmental factors and genetic ones (i.e. the latter, the “heritability).

Drum roll please…the results revealed:

About 40% could be blamed on genetics!


About 60% could be blamed on environment!

In other words, a complete, um, flip-flop of common wisdom and other recent research.  But don’t take it from me, here are some other autistic experts who can’t keep from wondering what happened in the numerical mumbo jumbo that is modern-day statistical modeling (i.e. elusive to most people except statisticians):

I think they’re really on shaky ground to say that,” said Dr. Paul Law, director of the Interactive Autism Network at the Kennedy Krieger Institute in Baltimore. (Autism Study Downplays Role of Genetics, LA Times)

“Their data is so similar to everybody else’s, and yet they come up with another conclusion,” said Robert Plomin, a behavioral geneticist at King’s College London. “I don’t know how this happened.(Autism Study Downplays Role of Genetics, LA Times)

“When somebody gets a totally different answer from what anyone else has seen, you need to see it a few more times before you believe it,” says Susan Folstein, a child psychiatrist at the University of Miami in Florida and autism researcher. (Environment Blamed For Autism, Science News)

So first and foremost, we have the issue of a freakish finding.  In other words, we need to await replication to validate these figures, especially the heritability and concordance among fraternal twins.

If only we could tell the classics from the mere trend.  Of course it’s possible the results will be replicated, but there is some reason not to buy this just yet. 

It’s worth noting how many twins from the solicited sample ended up “participating” in the study. Not many.  Originally researchers gathered 1,156 eligible pairs but ended up with only 192.  Less than 20% of the original sample and that’s worrisome especially if you’re trying to look at a complex issue riddled with numerous variables.  It’s not just my opinion either.

“That is too low of a response rate to marketing survey research, much less an epidemiological study,” says Edwin Cook, a child psychiatrist at the University of Illinois at Chicago. (Environment Blamed For Autism, Science News)

Why? For one the families who participated could differ in substantial ways from those who passed on the study.  Maybe in the participating families both twins were more likely to have autism thus making them more motivated to say yes.  That would explain the higher heritability rates too.  Also, studies with low participation are simply more prone to error, you know, the freak factor.

It’s clear the old ENVIRONMENT v GENES is a tired dichotomy much like the stale choice of either flats or four-inch heels choice in the women’s shoe aisle.  I think it’s time to seek some middle ground in both epidemiology and ladies’ footwear.  The roots of autism, just like women’s feet, clearly cannot be comfortably squashed into the present either/or options.  Our kids and our feet deserve more nuance.  

In fact, our notions of environment and genes need an overhaul.  Environment is not just about toxic cleaning supplies and bad plastic.  Let’s let Heather Turgeon over at Babble‘s Science of Kids explain it:

When we think environment, we tend to imagine toxins, diet, or unhealthy family conditions swooping in and altering a child’s biology or behavior. But it’s much more intricate and subtle than that. Anything that affects the expression of our underlying genetic code is considered the environment. It’s a loose term that encompasses even the most subtle (and less sexy, news-making) molecular signals in the womb that alter the expression of our genes. During all fetal development – healthy or otherwise – chemical switches are constantly turning off and on certain pieces of DNA. (Is Autism Linked to the Environment?, Babble)

Heather also reminded us that a recent review of autism research in Pediatrics identified 16 factors linked to autism. The suspects include multiple births, low birth weight, parental age, fetal distress, umbilical cord complications – many overtly “environmental” in nature, some that suggest genetic contributions too, like perhaps parental age  (i.e. faulty DNA?) thus blurring the line between the two. 

Speaking of which, genetics doesn’t just boil down to DNA.  The burgeoning field of epigenetics suggests what your grandma ate just might influence whether or not your child’s DNA will be destiny or merely a suggested route even though she or he got grandma’s same DNA.  Clearly genes are not what they used to be. 

So just as I’ve stayed clear of flip flops, ballet flats and heels (shorts and heels, really? cannot pull that off even living in Jersey), I’m also throwing out the clunky genes v. environment.  It’s time to clean out our epidemiological closets. 

Now if someone would refer me to the perfect 2-inch summer sandal that I can wear all day and won’t make me sentimental for my days working as the sole straight woman at an all-natural women’s clothing catalog, I will love you forever or until the rubber soles disintegrate.

By the way, I wonder what heels Heather Turgeon at Babble is wearing these days? Maybe she will reveal her footwear preferences? She writes with clarity about complex matters in such a calm and reassuring voice I bet she is also a terrific therapist with a good pair of shoes.

All thoughts on autism or sandals kindly accepted…