Model of the AVPR2 gene with the chromosomal map of a submicroscopic deletion found in the patients described. The location of the submicroscopic deletion within the q28 region of the chromosome X between the L1CAM and C1 genes loci is shown. The upstream breakpoint was identified within the intergenic region between L1CAM and AVPR2 genes, while the downstream breakpoint was identified within the intron 21 of the C1 gene by PCR screening, resulting in deletion of the whole AVPR2 gene and the last exon (exon22) of the C1 gene. To identify the exact positions of the deletion breakpoints, a primer pair 7F/9R was used to amplify interstitial genomic sequence. The 1160-bp fragment was obtained and sequenced.