Although the root cause(s) of stuttering remain unknown, evidence has accumulated from twin and adoption studies that genetics plays a role. Dennis Drayna, a geneticist at the National Institute on Deafness and other Communication Disorders (NIDCD), undertook a study to identify the genes involved in the disorder with the ultimate goal to elucidate poorly defined neural structures and functions regulating human speech. Results from the study were reported recently in the New England Journal of Medicine .
The study focused on a Pakistani family in whom previous work had determined that stuttering was linked to the long arm of chromosome 12 (chromosome 12q). In addition to the affected and unaffected members of these families, the study also included 123 Pakistani stutterers who were unrelated and 270 stutterers from the United States and England. Children under the age of eight were excluded, as they often recover from stuttering, as were people with neurologic or psychiatric symptoms. The control group (non-stutterers) consisted of 96 Pakistanis and 276 North American whites.