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From: Dennis Drayna
Date: 17 Oct 2011
Time: 15:00:52 -0500
Remote Name: 165.112.47.66
The ~10% figure comes from the following observation. Among unrelated individuals who have a family history of stuttering, sequencing the DNA of the GNPTAB, GNPTG, and NAGPA genes will identify a mutation in 9% of this group. A mutation is defined as a variant that changes an amino acid in the gene product that is evolutionarily conserved and judged to be damaging by the various computer programs that make such judgements, and does not exist in a large number of neurologically normal control subjects. Most of our mutations have been observed in more than one affected individual (although we have some that we've only seen in a single individual), and a couple have been observed many times.