Charcot-Marie-Tooth disease: a gene-dosage effect.

A broad spectrum of inherited neuropathy has been traced to three myelin genes, yet in the two most common disorders, there is no mutated gene. Instead, a gene has an extra or missing copy, as part of a 1.5-megabase DNA duplication or deletion. Eventually, duplications may emerge as a large fraction of all mutations. The discoveries have implications even for acquired disorders--including carpal tunnel syndrome.