Thursday, November 20, 2008
Two types of genes?
I have spoken about my view before, that stuttering might well be a two-phase disorder, see here . Adult stuttering is the result of causes that lead to onset of stuttering and causes that lead to non-recovery from onset of stuttering. Maybe this structure extends to genes. There are stuttering genes and there are recovery genes. Put yourself in nature's shoes, you have all these early humans stuttering and it affects survival rates. Nature can either select out the bad stuttering genes, OR it can select in good recovery genes. If we assume stuttering is only genetics, then from 100 babies 5 have the stuttering genes, and 4 have recovery genes, which leaves us with 1%, the adults who stutter. The picture is of course more complicated, because it is not 100% genetics but you get the twist. If this dynamics is dominant, the search for genes will be more complicated, because currently the trait is adult stuttering whereas the trait should really be ever-stuttered-as-a-child.
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I believe the "stuttering genes" are just bad copies of normal genes which usually have normal function. It could be genes important for development (including development of speech region). In that case, stuttering is the result of errors in developmental program.
The stuttering could be the result of brain damage, e.g. neuroinfection or problems with childbirth (which for example could cause hypoxia and therefore neurons death in speech area). In latter case, "the stuttering genes" are just bad copies of genes responsible for coping with hypoxia.
I mean, having these bad copies of genes just increase the probability of stuttering but don't lead to stuttering in 100% cases. There could be hundreds of such genes, the worse combination of bad/good copies you have - the higher your chanses to suffer from stuttering.
The recovery from stuttering is the same story. It should involve the formation of new connections between neurones and probably of new neurones themselves etc. Any genes involved in these processes could influence recovery from stuttering. If you have bad copy of gene, the probability to recover from stuttering lowers. Again, it could be hundreds of genes, and the combination of good/not-so-good/bad copies of genes is important. I think in some cases, even if you have perfect combination of good copies of "recovery genes" you don't recover.
Evolution leads to selection of good copies of genes and eliminate bad copies.
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