Completion of the physical map of Xq28: the location of the gene for L1CAM on the human X chromosome.

The gene for the neural cell adhesion molecule L1 (L1CAM) has been shown to be located close to the color vision pigment genes in mouse and man. This location has been confirmed by a number of different mapping strategies in both species. With pulsed field gel electrophoresis it has been proposed that L1CAM lies between the RCP, GCP, and GDX, G6PD loci. We report here a reinterpretation of the location of this gene, based on the physical linkage of L1CAM to the more proximal locus DXS15. This places L1CAM between this marker and the color vision genes (RCP, GCP), a region very dense in CpG islands, expected to contain a large fraction of the disease genes assigned to the Xq28 region. In combination with the physical mapping data on Xq28 described previously, this closes the last remaining gap in the map of the Xq27-Xq28 region. This removes the last contradiction between the maps of this region in the genomes of man and mouse, and confirms the close similarity of order and distances of markers between these organisms.