ESTIMATION OF THE SIZE OF THE CHROMOSOME 17P11.2 DUPLICATION IN CHARCOT-MARIE-TOOTH NEUROPATHY TYPE-1A (CMT1A)

We have previously shown a duplication in 17p11.2 with probe pVAW409R3 (D17S122) in 12 families with hereditary motor and sensory neuropathy type I (HMSN I) or Charcot-Marie-Tooth disease type 1 (CMT1). In this study we aimed to estimate the size of the duplication using additional polymorphic DNA markers located in 17p11.2-p12. Two other 17p11.2 markers, pVAW412R3 (D17S125) and pEW401 (D17S61), were found to be duplicated in all HMSN I patients tested. Furthermore, all HMSN I patients showed the same duplication junction fragment with probe pVAW409R3. On the genetic map the duplicated markers span a minimal distance of 10 cM while on the physical map they are present in the same NotI restriction fragment of 1150 kb. The discrepancy between the genetic and physical map distances suggests that the 17p11.2 region is extremely prone to recombinational events. The high recombination rate may be a contributing factor to the genetic instability of this chromosomal region.