[Digest] The Science of Stuttering: Speech Therapy
DOWN the ages stuttering has been blamed on many things. In the second century Galen pinned it on a dryness of the tongue. In the 17th, Francis Bacon reckoned a stiff tongue was responsible. In the 19th, surgeons suggested too large a tongue. In the 20th, parental neglect and even an unfulfilled urge for oral sex had their moments of fame (“The King’s Speech”, a film competing for Oscars this week, stresses psychology). The suggested remedies were just as diverse. Galen thought wrapping the patient’s tongue in a cloth soaked in lettuce juice might help. Bacon recommended wine. The Victorians wielded scalpels. The psychiatrists, the couch. None of it worked (except in the movies).
These days, as delegates to the AAAS meeting in
Dennis Drayna of
To discover which genes might be responsible, Dr Drayna looked at 44 Pakistani families. Marriage between cousins is common in
Further study of South Asians has shown that mutations in two other genes, GNPTG and NAGPA, are found in individuals who stutter, but not in non-stutterers. All three affected genes encode enzymes that regulate lysosomes, the cell’s waste-disposal units. Two of the mutations involved are also known to cause a rare disease called mucolipidosis. Severe mucolipidosis is fatal within ten years of birth. Even the mild variety has symptoms that include abnormal skeletal development and, sometimes, slight mental retardation.
Fortunately for stutterers, close examination of those with the relevant mutations reveals no symptoms of mucolipidosis. Dr Drayna suspects that both conditions are caused by misfolding of the enzymes in question, but that the details are different. With stutterers, he thinks, a specific group of brain cells involved in speech production is, for an unknown reason, uniquely sensitive to the enzymatic glitch—perhaps producing the patterns seen by Dr De Nil in his brain scanners.
To investigate further, Dr Drayna is now attempting to splice human stutter-causing genes into the DNA of mice. That, of course, raises the question of what a stuttering mouse sounds like. To the human ear, it may not sound like anything. Many murine squeakings are too high-pitched to be perceptible. But ultrasonic detectors should deal with that. With luck, the causes of stuttering should soon be understood better. Whether that results in treatments more effective than lettuce juice and wine is another matter.
