Pericentromeric gene duplication and genetic instability. The propensity of chromosomal regions 22q11, 15q11, and 17p11 to undergo microduplication/microdeletion is shown. Most common breakpoint regions are indicated by horizontal bars. The map locations of known intrachromosomally duplicated gene segments are shown as solid boxes in relation to genetic markers of these regions. More intrachromosomal duplicated copies of the GGT-like repeat block [which consists of variable smaller repeat units of the γ-glutamyl transferase (GGT) and breakpoint-cluster-like (BCR) genes] exist than are shown. Similarly, multiple copies of the ERY-1 gene have been identified within each cluster as well as copies located within 16p11.2 SMS–REP represents a duplicated gene cluster (>200 kb) composed of multiple genes [signal recognition particle, a keratin gene (KER-I), a coactisin gene (CLP), and the TRE oncogene]. The CMT1A–REP duplication segment consists of a portion of the COX10 gene as well as a novel cDNA, C170RF1. Many other pericentromerically duplicated segments identified within these regions have not been assigned to this map.