Stuttering or stammering affects people of all ages and races and most often starts between the ages of two and five, when children start to develop language skills. Although most children outgrow stuttering, about one percent of adults continue to stutter. The underlying causes are not well understood but stressful situations can make stuttering more severe and, especially in the past, the condition was believed to have a social or emotional component. It has now been recognised that developmental stuttering runs in families and a section of chromosome 12 has been linked to stuttering in a group of Pakistani families. In a study published in the New England Journal of Medicine, researchers at the National Institute on Deafness and Other Communication Disorders (NIDCD) have now refined the location on chromosome 12 to mutations in three genes, GNPTAB, GNPTG and NAGPA, which encode proteins involved in lysosomal recycling of unwanted cellular components. Mutations in two of these genes had previously been linked with rare, and often fatal, lysosomal storage disorders.
Although only a small proportion of stutterers are likely to have these genetic mutations, the study is the first to pinpoint specific gene mutations as a potential cause of stuttering. Recently, enzyme replacement therapy has been developed to treat lysosomal storage disorders and, if the mutations involved in stuttering also prove to involve loss of enzyme function, such treatments could eventually also be effective for this group of stutterers.