Relationship between Charcot-Marie-Tooth 1A and Smith-Magenis regions. snU3 may be a candidate gene for the Smith-Magenis syndrome.

The juxtacentromeric region of the human chromosome 17 short arm (17p11.2-p12) contains genes involved in the Charcot-Marie-Tooth type 1A disease (CMT1A) and the Smith-Magenis syndrome (SMS). CMT1A is associated with a duplication of a short segment whereas SMS is linked to microdeletions, extending toward the centromere. We describe the construction and analysis of a 5 Mb YAC contig spanning the CMT1A duplicated segment and the distal part of four SMS microdeletions. We concluded that the YAC contig contains about 1Mb of genomic DNA which is deleted in the four SMS patients analysed. Moreover two YACs contain both STS deleted in SMS (U3) and STS duplicated in CMT1A (5H5), but the proximal breakpoint associated with the CMT1A duplication is not the same as the distal SMS breakpoint we studied. Finally we located five new STS in SMS deletion. Two of them, a microsatellite (D17S805(23)) and the gene coding for small nuclear RNA U3, have been localized in the contig we described. We may also note that snU3 is the first expressed sequence localized in an SMS deletion so far. The possible participation of this gene in the SMS phenotype is discussed.