The Prof Is In

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Re: stuttering in families

From: Dennis Drayna, PhD
Date: 19 Oct 2009
Time: 14:46:42 -0500
Remote Name: 165.112.46.84

Comments

Regarding JM's original question on how stuttering gets started in a family, many of the previously posted comments address this very well, I think, and I just have a few things to add. First, the generally accepted figure is that about half of stuttering occurs in the presence of a family history. For these cases of stuttering, we can make some good guesses as to how it got started in the family. One possibility, as Tom Weideg has noted, is that a genetic variant has arisen that somehow provides some advantage, but at the same time causes stuttering. This could certainly be true, but another possibility is that no such advantage exists, and such genetic causes of stuttering are simply nature's ongoing production of natural variation in our genes. The great majority of this variation is not helpful to the organism, but it can take natural selection many generations to eliminate it from the population. In fact, the figure of 50% of stuttering being due to genetic causes may be an underestimate. We know that using the presence of family history as a measure of gene frequency underestimates the true frequency of the genetic variants that cause many inherited disorders. So, a large fraction of cases of stuttering, even those with no obvious family history, could be due to genetic factors, and a "stuttering gene" may have previously existed in a family, perhaps for a long time, without being recognized. However in all cases, stuttering due to genetic causes comes from the appearance of a new mutation, which could have happened recently or at some time in the distant past. Now that we're beginning to make some progress identifying the genes that cause stuttering, it will be possible to answer some of these questions. I should also note that a large amount of stuttering is clearly not due to inherited causes. We don't understand these other causes very well at the moment, but of course these cases of stuttering typically occur in just that one individual, and are not passed down to anyone else in the family.


Last changed: 10/23/09