A duplication in chromosome 17 responsible for most cases of autosomal dominant HMSN 1 was present as a de-novo mutation in 9 out of 10 sporadic patients examined at the Department of Neurology, Academic Medical Center, Amsterdam, The Netherlands. 
COMMENT. The previous assumption that isolated cases of HMSN I are most frequently autosomal recessive appears to be incorrect and testing for the duplication in chromosome 17 is essential to establish the mode of inheritance for genetic counseling of isolated patients.
This duplication of part of chromosome 17 was found in affected individuals from 7 of 8 families with HMSN I. Patients with HMSN type II do not show the duplication. 
HMSN type I also known as Charcot-Marie-Tooth disease type I is known to be genetically heterogeneous. At least 5 genetic loci have been identified including 3 dominant genes and 2 X-linked recessive genes. Ionasescu VV et al. from the Department of Pediatrics, University of Iowa Hospitals, Iowa City and the Massachusetts General Hospital present a clinical and genetic linkage study of 8 families with X-linked dominant Charcot-Marie-Tooth neuropathy which supports a localization of the diseased gene between DXS14 and DXYS1.