The present invention relates to defects in periaxin (PRX) associated with myelinopathies, including Charcot-Marie-Tooth syndrome and/or Dejerine-Sottas syndrome. Unrelated individuals having a myelinopathy from Dejerine-Sottas syndrome have recessive PRX mutations. The PRX locus maps to a region associated with a severe autosomal recessive demyelinating neuropathy and is also syntenic to the Prx location on murine chromosome 7.