To better understand mechanisms involved in the evolutionary origin of LCR22s, their sequence composition and architectural features were analyzed. The LCR22s comprise 12% of the 22q11.2 interval and are composed of blocks or modules harboring known genes, pseudogenes, and predicted genes (26,67). They are 10-250 kb in size, contain a variety of blocks in direct and inverted orientations (Fig. 5). The genes within (USP18, GGT, BCR, GGTLA) have become duplicated during evolution, thereby shaping the architecture of LCR22s (Fig. 5). The full-length functional genes each lie in different LCR22s, whereas duplicated copies are present in many of them (68). Because the genes comprise a significant part of the LCR22s, they can be used to understand their evolution. Although important for the evolution of LCR22s, they are not likely candidates for the malformations in VCFS/DGS patients as the copies in the deleted region are non-functional pseudogenes.
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