Fraction of the
human population
percent that stutters
Genes may explain some stuttering
goes awry on a large scale, the result can
be a fatal cascade of cell death, tissue
damage and organ failure, says study
coauthor Dennis Drayna, a geneticist
also tested 96 people in Pakistan and at the National Institute on Deafness
Defects on chromosome 12 found in small portion of cases
By Nathan Seppa
276 in North America who didn’t stut- and Other Communication Disorders
After testing hundreds of people who ter, as a control group. in Rockville, Md.
stutter, researchers have nailed down In 21 of the stutterers, the researchers But people who stutter, including par-
defects in three genes that may account found that one of three genes on chro- ticipants in the new study who tested
for a fraction of cases, researchers report mosome 12 was mutated, a rate of about positive for one of the three mutations,
in the Feb. 25 New England Journal 5 percent. Only one of these mutations typically have no such dire disease.
of Medicine. showed up in a nonstutterer, in one of Syuichi Ooki, a physician at Ishikawa
Scientists don’t fully understand why the Pakistani controls. None occurred Prefectural Nursing University in
most children who stutter overcome it, in the Western controls. Kahoku, Japan, wasn’t surprised that
why stuttering persists in others and Allthreegenescarryingthemutations these mutations appeared in genes
above all, what causes the condition. encode enzymes that play a role in the involved in a rudimentary area of cell
In the new study, scientists examined proper function of lysosomes, compart- metabolism. Mutated genes can lead to
genes on a specific strand of chromo- ments that serve as cellular recycling a chain of events and induce unforeseen
some 12, previously linked to stuttering, centers. Extraneous materials are pulled biological changes, Ooki says. “There-
using DNA obtained from 123 stutter- into lysosomes, where the materials are fore, mutation of genes involved in a
ers in Pakistan and 270 in the United chopped up and digested. basic metabolic process can unexpect-
States and England. The researchers If the recycling process in lysosomes edly affect human behavior.”
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