Thursday, January 17, 2008

Twins: Little shared environmental effect

I have just re-read the 13000-twin study by Katherina Dworzynski et al and she clearly empirically confirms what I have been saying in my last posts:
Stuttering appears to be a disorder that has high heritability and little shared environment effect in early childhood and for recovered and persistent group of children by age 7.
And further,
With respect to the genetic effects throughout, it also needs to be emphasized that, even though substantial estimates of heritability were obtained, many monozygotic twin pairs were discordant for stuttering. This is further evidence for the importance of the child's unique environmental influences, in that specific stressors have unique effects when a genetic liability is present.
Again, the nature vs nurture fallacy is revealed. It is simply wrong to divide the world into nature and nurture. There are three categories: the genes (nature), unique environmental stressors (more or less random events), and shared environment effects (nurture). Think about being the CEO of a small start-up company. Unique events like you having a car accident or a virus infection, sheer bad luck, pregnancy of your most important employee, and so on can completely change the outcome of your company's success because you only have a few months of financing to hit a certain target before your bank or venture capitalist cuts financing (window of development for child). I have seen this many times. Of course, you are especially vulnerable to such events if you have a bad or weak business plan (think of this as the genes - the instructions on what to do). General market conditions are also important but not that crucial, and can increase or decrease vulnerability. I never thought that venture capital, the topic of a book I have written (see here), is relevant to stuttering! :-)


Scott said...

Hey Tom, love the web-site. Still infatuated with Pagoclone. Sad that after all these years this is the only medication that carries any hope. Sure hope the limited number of stutters and corresponding limited amount of profit froma particular drug is not at the root of the drug industries lack of attention to this issue.

Also, am a mild stutterer and my oldest son is too. Cleary genetic as my two youngest children are perfectly fluent.

Keep doing what your doing..

Anonymous said...

Hi Tom, I have a question which is not directly correlated to the topic:

It is known that some nations have faster speech rates than others, even if they speak the same language. E.g. in New Zealand people speak faster than in Australia. Is there any dependence observed in the ratio of recovered kids growing up in "slower vs. faster speaking" countries? For example do more children recover from stuttering in Finland than in Spain?
Speaking slowlier is a common technique for getting stuttering under control. Could it be that most PWS become more fluent when speaking slowly because they speak differently? The same effect is observed when we imitate or speak with foreign accent.

Tom Weidig said...

I am not aware that there are major difference between culture in terms of stuttering.

I am not excluding that in some countries the stuttering prevalence is slightly lower due to speaking rates.

But even if speaking rate is a factor, there are many more factors, and though diluting the influence of the speaking rate.

Speaking slowly has two different effects:

a) you are just speaking more slowly. so your brain has more time to do its work.

b) you are exerting active control of your speech as opposed to your normal speech rate where you talk without thinking too much about how you speak.

Speaking with a foreign accent and imitation falls into category b.

Tom Weidig said...

Hi Scott,

glad you like my website. Note my use of like as opposed to love, we European use it more sparingly! :-)

I think the crucial question is not so much whether they make money but whether it is highly effective or not. And that's a big question mark.

"Clearly genetic as my two youngest children are perfectly fluent."

It is not 100% genes. Did the two younger kids stutter at some point?


Anonymous said...

Interesting also re: siblings. Our daughter stuttered significantly for several months around age 3. She did not stutter as early as our son (2+), but it was as severe and with more secondary features. Then she stopped, and no longer stutters. I almost forgot, it's been 4+ years.

Anonymous said...

I was also going to comment on rate of speech...
We're from the New York area--known for it's fast rate of speech. When our son first went for speech therapy, we were supposed to try to talk slower to model slower speech (VERY HARD TO DO!). We really were never successful. But, our son is nearly always fluent when really angry (almost never :-) or when giving opening/ closing statements for "Teen Court." So when adrenaline is really high?