Abstract
A 3-year-old girl with rare and unique myelin abnormality in the sural nerve is described. Her parents are first cousins. Her clinical features were similar to those of HMSN Ⅰ. Therefore, a diagnosis of autosomal recessive form of HMSN was made. However, in histopathologic studies of the sural nerve, it was observed that the folded myelin did not extend into the axon but into the outer portion of Schwann cell cytoplasm, so called excessive myelin outfolding. The density of both the myelinated and unmyelinated fibers was less in the patient than in controls. In recent years, the patient described above is usually classified under HMSN ⅣB or (Charcot-Marie-Tooth disease) CMT4B, and molecular genetic studies are now in progress.
