Autosomal dominant Charcot-Marie-Tooth type-1A neuropathy (CMT1A) is a 
demyelinating peripheral nerve disorder that is commonly associated with a 
submicroscopic tandem DNA duplication of a 1.5-Mb region of 17p11.2p12 that 
contains the peripheral myelin gene PMP22. Clinical features of CMT1A include 
progressive distal muscle atrophy and weakness, foot and hand deformities, gait 
abnormalities, absent reflexes, and the completely penetrant electrophysiologic 
phenotype of symmetric reductions in motor nerve conduction velocities (NCVs). 
Molecular and fluorescense in situ hybridization (FISH) analyses were performed 
to determine the duplication status of the PMP22 gene in four patients with rare 
cytogenetic duplications of 17p. Neuropathologic features of CMT1A were seen in 
two of these four patients, in addition to the complex phenotype asociated with 
17p partial trisomy. Our findings show that the CMT1A phenotype of reduced NCV 
is specifically associated with PMP22 gene duplications, thus providing further 
support for the PMP22 gene dosage mechanism for CMT1A.