(CMT, the most cotton genetic neuropathy, is a worldwide problem that cripples people at the peak their earning power. According to McKusick. Charcot-Marie-Tooth disease has a frequency of about 1 in 25OO with about 90% of the cases transmitted in an autosomal dominant fashion.) Two autosomal CMT loci have been established: one locus linked to the Duffy blood group locus near the centromere on chromosome 1, and one locus unlinked to Duffy. (An X-linked CMT locus is four centimorgans from the phosphoglyceromutase locus near the centromere.) We are searching for the different CMT genes by """"""""reverse genetics."""""""" This process first moves ever closer to a disease locus by testing segregation of mapped, polymorphic DNA markers with a disease phenotype in human pedigrees. To expedite this search we are testing DNA fragments from a sorted chromosome I library we cloned in EMBL-4 phage that have been localized near the centromere by spot blot analysis. Candidate genes mapped near the centromere will be tested simultaneously. When the approximate location of CMT has been identified, the area will be saturated with other linked polymorphic sites that are ordered. To expedite this process, chromosomes from individual patients in many pedigrees including all patients with two genetic diseases are being karyotyped to look for microscopic chromosome deletions. If found, these deleted chromosomes will be sorted from normal chromosomes and tested to locate more fragments in the deleted region by spot-blot analysis. (When a linked polymorphic fragment is identified within two centimorgans, somatic cell hybrids with a human chromosome 1 will be irradiated, fused with control hamster cells, and cell strains chosen that still carry the polymorphic segment. Cell strains will be selected for the least amount of human DNA that still carry the closely linked polymorphic fragment and do not carry more distant polymorphic fragments. Then methylation-free islands in this DNA segment will be selected to identify putative genes and to test zoo blots and cDNA libraries for appropriately expressed genes that could cause the disease.) Polymorphic restriction fragments closely linked to the disease locus will be used for prenatal diagnosis of at-risk fetuses. Ultimately identification of the defective CMT gene could lead to more effective treatment
