Charcot-Marie-tooth disease 1A (CMT1A) associated with a maternal duplication of chromosome 17p11.2-->12.

We report here the second case of Charcot-Marie-Tooth disease 1A (CMT1A) with a cytogenetically visible de novo direct duplication of 17p11.1-->17p12. A male child who was initially referred for developmental delay and dysmorphism was subsequently shown to have significantly reduced motor nerve conduction velocities characteristic of CMT1A. This patient was not informative for the DNA markers mapping to the CMT1A region; however, with DNA markers pA10-41 and EW503 that map proximally and distally with respect to the disease locus, a dosage difference was observed between the two alleles. Comparison with parental genotypes indicated a de novo maternal duplication. Pulsed field gel analysis using probe VAW409R3a indicated that a 500-kb SacII junction fragment usually associated with CMT1A was absent in this patient. These findings confirm that the disease phenotype is probably caused by a gene dosage effect.