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Drayna , who worked at the National Institute on Deafness and Other Communication Disorders , already had a longstanding interest in the inheritance of stuttering . His uncle and elder brother stuttered , and his twin sons
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If you ’ re worried about your child ’ s language development , schedule an appointment with a speechlanguage pathologist sooner rather than later , advises Michigan State University speech-language pathologist Scott Yaruss .
Therapy is most effective if it ’ s started early and nears completion around age 6 or 7 , a time when the young brain is still malleable . But therapy can certainly help older people handle their stutter , too . For more information :
• Stuttering Foundation
• National Stuttering Association
• Friends : The National Association for Young People Who Stutter
• SAY : The Stuttering Association for the Young
— Amber Dance did so as children . But he was reluctant to make a transatlantic journey based on an email , and wary that his clinical skills weren ’ t up to analyzing the family ’ s symptoms . He mentioned the email to current National Institutes of Health director Francis Collins ( director of the National Human Genome Research Institute at that time ), who encouraged him to check it out , so he booked a ticket to Africa . He has also traveled to Pakistan , where intermarriage of cousins can reveal gene variants linked to genetic disorders in their children .
Even with those families , finding the genes was slow going : Stuttering isn ’ t inherited in simple patterns like blood types or freckles are . But eventually , Drayna ’ s team identified mutations in four genes — GNPTAB , GNPTG and NAGPA from the Pakistan studies , and AP4E1 from the clan in Cameroon — that he estimates may underlie as many as one in five cases of stuttering .
Oddly , none of the genes that Drayna identified have an obvious connection to speech . Rather , they all are involved in sending cellular materials to the waste-recycling compartment called the lysosome . It took more work before Drayna ’ s team linked the genes to brain activity .
They started by engineering mice to have one of the mutations they ’ d observed in people , in the mouse version of GNPTAB , to see if it affected the mice ’ s vocalizations . Mice can be quite chatty , but much of their conversation takes place in an ultrasonic range that people can ’ t hear . Recording the ultrasonic calls of pups , the team observed patterns similar to human stuttering . “ They have all these gaps and pauses in their train of vocalizations ,” says Drayna , who cowrote an overview of genetics research on speech and language disorders for the Annual Review of Genomics and Human Genetics .
Still , the team struggled to spot any clear defect in the animals ’ brains — until one determined researcher found that there were fewer of the cells called astrocytes in the corpus callosum .
About 80 percent of kids who stutter grow up to have normal speech patterns , while the other 20 percent continue to stutter into adulthood .