The nomenclature, classification, and genetic basis of Charcot-Marie-Tooth (CMT) disease are reviewed from the Department of Molecular and Cell Biology, University of Aberdeen Medical School, Scotland. Electrophysiological examination with nerve conduction studies and nerve pathology allow subdivision of CMT disease into two major types, CMT type 1 and type 2. CMT 1, also called hereditary motor and sensory neuropathy (HMSNI) is most common and is characterized by slow nerve conduction velocities (NCV), and “onion bulbs“ in nerve biopsy due to demyelination and remyelination. CMT2 (HMSNII) has normal NCVs and myelination but marked axonal degeneration. CMT is both clinically and genetically heterogeneous. The duplication of a 1.5 Mb DNA fragment on the PMP22 gene of chromosome 17p11.2 is associated with more than 70% of CMT1 cases. Point mutations of the PMP22 gene are also associated with CMT 1 phenotype. PMP22 duplication testing is the initial screen in CMT disease diagnosis, accounting for 70% of CMT1 cases. Cx32 screening will uncover the second most common genetic defect. 
COMMENT. A longitudinal clinical and electophysiologic study of Charcot-Marie-Tooth disease type 1A with 17p duplication in infancy and early childhood is described from the University Hospital “Marques de Valdecilla,“ Santander, Spain . Twenty at-risk children from 6 unrelated CMT-1A families were examined in the first 5 years of life, and 12 were affected. Initially 2 had symptoms, and 5 were symptomatic at the last exam. MCV and SCV were abnormal in 50% at the beginning and in 83% at conclusion of study. After 2 years of age, all affected children had abnormal MCV, SVC, and F-waves. Serial electophysiologic studies can detect the CMT-1A gene carrier in infancy.