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From: Dennis Drayna
Date: 13 Oct 2005
Time: 10:29:26 -0500
Remote Name: 165.112.46.123
Hi Corrine, Thanks for your question. The genetic factors in stuttering are clearly a group of different things, all inherited. Finding a gene on chromosome 12 that causes stuttering in Pakistani families and another on chromosome 1 in African families was just what us geneticists expected. For example, most deafness in children is due to genetic causes, and in total this is due to mutations in about 75 known genes, scattered on all the different human chromosomes. The deafness in any one family is almost always due to a single one of these genes. Thus when we study different families or populations, we fully expect to find genes in different locations. Another example you might be familiar with is muscular dystrophy, where there are over three dozen different genes on different chromosomes that can cause this disorder in the population as a whole, with one single gene at work in any given family. The situation where mutations different genes cause the same disorder is so commonplace that geneticists even have a name for it - it's referred to as locus heterogeneity. It is very true that no one specific gene is responsible for stuttering in the population. However, careful analysis of hundreds of families (including some very large ones) in which stuttering clusters tells us that in these cases, stuttering is not due to environment, upbringing, or relations between family members. Finally, not all stuttering is due to inherited factors. It has been estimated that perhaps half of all cases of stuttering are due to genetic causes. The other half are due to unknown causes, but may be associated with things like low birth weight.