The Charcot-Marie-Tooth Syndrome : a population genetic study in South Wales
The Charcot-Marie-Tooth (CMT) syndrome comprises a heterogeneous group of disorders affecting the peripheral nerves and anterior horn cells of the spinal cord. They constitute a significant proportion of the burden of disability due to the single gene neurological disorders, with a prevalence of 18.1 per 100000 of the South Wales population. The clinical manifestations of these disorders have been documented and their severity assessed using a standard protocol. The commonest disorder in the group is type I hereditary motor and sensory neuropathy (type I HMSN) (prevalence 11.0 per 100000 population) which has been mapped using genetic linkage analysis to chromosome 17, band p11.2 (the CMT1a locus). There was no evidence of genetic heterogeneity (ie any locus other than that at 17p11.2) within the type I HMSN group in the study population. Families with type V HMSN and the spinal form of the Charcot-Marie-Tooth syndrome have been shown not to be linked to this locus in this study. A number of families gave inconclusive results due either to small family size or to lack of informativeness for the polymorphisms studied. It has been possible to document in 91% of affected individuals with type I HMSN, heterozygous for the Msp1 polymorphisms of locus D17S122, trisomy (using the cDNA probe pVAW409R3a) within band 17p11.2. This was not seen in any normal individuals nor in any case of the spinal form of the Charcot-Marie-Tooth syndrome nor in HMSN types II or V. The demonstration of this trisomy in individual cases and families not suitable for conventional linkage analysis provides a rapid means of determining affection status for the CMT1a mutation. Presymptomatic and prenatal testing for this disorder is now feasible for individuals who request it.