Fig. 5. Block structure of the LCR22s and genes within. The known genes, USP18 (68a), GGT (77), GGTLA (78), and BCR (79) and their pseudogene copies, comprise part of the LCR22s. We performed a comparative computational analysis of all the clones spanning the 22q11.2 region to identify similarities. We also took into account a recent annotation of the LCRs in chromosome 22 (67). The different regions of similarity are depicted by different colors. The genes and predicted genes, in their normal genomic organization with respect to the centromeres are shown. LCR22-3a has an uncloned region. The LCR22s are drawn to scale.

The three proximal LCR22s mediate the recurrent chromosome 22q11.2 rearrangement disorders (Fig. 1). Low stringency FISH mapping with LCR22 probes, revealed multiple signals on 22q11.2 and a few other chromosomes suggesting that they have been unstable during evolution (Fig. 6; [67-68]). As previously stated, the genes are present in a single copy in the mouse, on different chromosomes, and have therefore evolved more recently in primates. The sequences of the LCR22 genes and copies therein were compared by examining the 22q11.2 region to determine if there was a specific mechanism responsible for gene duplication (68).

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