Exclusion of the SCN2B gene as candidate for CMT4B

Charcot-Marie-Tooth disease type 4B (CMT4B) is a demyelinating autosomal recessive motor and sensory neuropathy characterised by focally folded myelin sheaths in the peripheral nerve. The CMT4B gene has been localised by homozygosity mapping and haplotype sharing in the 11q23 region. A cDNA encoding for the beta 2 subunit of the human brain sodium channel, SCN2B, has been recently assigned to the same chromosomal interval by FISH. The SCN2B gene has been considered a good candidate for CMT4B on the basis of protein homology, chromosomal localisation, and putative biological function of the coded product. In this paper, we report the genomic structure of the SCN2B gene consisting of 4 exons and 3 introns spanning a region of approximately 12 Kb. In addition, a search for mutations in patients affected with CMT4B as well as a refined physical localisation excludes SCN2B as the CMT4B gene.