Thursday, November 18, 2010

Yet more evidence for strong heritability from twin studies

Fagnani, Fibiger, and al. have just published a twin study using a database of over thirty thousand twins. Their findings are consistent with past twin study results (see on old post of mine on the Dworzynski study). They find a high heritability of 80%, and only moderate unique environmental effects. Note that they do not mention shared environmental effects.

This finding fits my view on stuttering. Genetics drives the onset of stuttering in many people. The other factors (alone or in combination with genetics) are internal developmental issues caused by unique environmental events like neurological incident, virus and head trauma. Only some of these events were reported in the twin study, so the effort is measured as moderate. Needless to say that, as in many other conditions, the social environment plays a negligible role in the actual onset.

Here is the abstract:

Heritability and environmental effects for self-reported periods with stuttering: A twin study from Denmark.

National Centre for Epidemiology, Surveillance and Health Promotion, National Institute of Health, Rome, Italy.

Abstract

Abstract Genetic influence for stuttering was studied based on adult self-reporting. Using nation-wide questionnaire answers from 33,317 Danish twins, a univariate biometric analysis based on the liability threshold model was performed in order to estimate the heritability of stuttering. The self-reported incidences for stuttering were from less than 4% for females to near 9% for males. Both probandwise concordance rate and tetrachoric correlation were substantially higher for monozygotic compared to dizygotic pairs, indicating substantial genetic influence on individual liability. Univariate biometric analyses showed that additive genetic and unique environmental factors best explained the observed concordance patterns. Heritability estimates for males/females were 0.84/0.81. Moderate unique environmental effects were also found.

3 comments:

Ora said...

Tom - Help us out here. You've read about and thought about this stuff a lot more than many of us have...

These recent findings on genetic links and heritability are certainly interesting and they add to scientific knowledge - and that in itself is a good thing.

But how might they be useful or valuable? How might they lead to treatment and improvement for us stutterers?

I can imagine that they might help in designing pharmacological therapies. Is this the most likely goal?

Are we envisioning genetically designed drugs, which target the genome, and somehow block the functioning of these genes, perhaps by blocking the production of genes by these proteins?

Or perhaps this knowledge might be used for diagnostic testing, perhaps to help identify subgroups which are more at-risk. For example, certain genotypes might be found to be highly correlated with persistent stuttering in children - i.e., stuttering that's not likely to go away on its own. One of the big challenges in treatment of children is to distinguish between those who will improve naturally, without treatment, and those who won't, so that limited treatment resources can be targeted on those who actually need them, and not wasted on those who are likely to recover on their own.

How do people in the stuttering research/treatment community think these genetic results might eventually be put to use?

Tom Weidig said...

Hi Ora,

>> But how might they be useful or valuable? How might they lead to treatment and improvement for us stutterers?

No, I don't think so. Except maybe for some whose gene mutation leads to imbalances that can be redressed pharmaceutically.

The gain will come mostly from understanding stuttering better.


>> I can imagine that they might help in designing pharmacological therapies. Is this the most likely goal?

maybe in identifying subgroups.


>> Are we envisioning genetically designed drugs, which target the genome, and somehow block the functioning of these genes, perhaps by blocking the production of genes by these proteins?

no, I don't think so. That is very dangerous and you can never been sure of what happens. I can only see treatments where the proteins that the mutation did not produce are added artificially, or "bad" proteins from the mutation are removed.


>> Or perhaps this knowledge might be used for diagnostic testing, perhaps to help identify subgroups which are more at-risk. For example, certain genotypes might be found to be highly correlated with persistent stuttering in children - i.e., stuttering that's not likely to go away on its own. One of the big challenges in treatment of children is to distinguish between those who will improve naturally, without treatment, and those who won't, so that limited treatment resources can be targeted on those who actually need them, and not wasted on those who are likely to recover on their own.

YES. this could be one avenue. diagnostics.


>> How do people in the stuttering research/treatment community think these genetic results might eventually be put to use?

I don't know, but some dream of a gene replacement therapy but this will not come any time soon. Not before I retire!

Anonymous said...

Gene therapy has not worked for any disorder successfully. It will not work and it is costly. The aim should be to find out the proteins associated with disorder and identifying its functions. For drug development, proteins need to be blocked or augmented or modulated depending upon the requirement. The problem with us is that sufficient model will not be available for study. Can we use mouse as a model? HaHaHa...The primitive models such as yeast, mammalian cell lines will be helpful with respect to modulating the function of the protein.I think the existing drugs such as paglacone and similar known CNS active drugs just will be modified chemically to generate new drug.
Complete new molecule will not be possible because of ineffective models. We will be remain untreated till the end of the world except psychologically treatment which will reduce our stuttering. There is a need for huge improvement in technology which will work at the genetic level effectively and at the embryonic stem cell level.