In 1992 the gene problem that causes Charcot-Marie-Tooth (CMT), the most common hereditary neuropathy was identified by Dr. James Lupski, in Houston, Texas. CMT is associated with a duplication on chromosome 17p11.2-12. This chromosome contains an important myelin gene, peripheral myelin protein-22 gene (PMP22). CMT has an extra copy of PMP22. A year later, in 1993, Dr. Phillip Chance, et al, discovered that HNPP is caused by a deletion (loss of a copy) of PMP 22 on the same chromosome where CMT has a duplication. Two copies of a gene are usually needed for normal function.
The discovery of the genetic problems causing HNPP and CMT has brought HNPP to the attention of more researchers. Both disorders are related to problems with the myelin sheath, the covering on the nerves. Both disorders seem to have a wide variety of symptoms and degrees of severity. CMT, however, is considered a more severe disorder than HNPP possibly in part to CMT usually developing in childhood.
The Muscular Dystophy association also has an explanation of the genetics of HNPP.
http://www.mdausa.org/experts/ask_cmt.html - scroll down throught the CMT information to 4/96 "HNPP a form of CMT?".
Last updated: 1/00
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