The human genome contains numerous sites where the presence of complex low-copy repeated sequences leads to recurrent chromosomal rearrangements resulting in recognizable syndromes. Typically, mispairing and crossing over between adjacent direct repeats, resulting in the deletion of the intervening DNA, cause these syndromes. Such microdeletion syndromes include deletions of 22q11 (DiGeorge/velocardiofacial syndromes or DGS/VCFS), 7q11 (Williams syndrome), and 15q11-q13 (Prader-Willi/Angelman syndromes or PWS/AS) (reviewed in Ref. [1]). Theoretically, such nonallelic homologous recombination between repeats should also result in an equivalent number of reciprocal microduplications. However, microduplication syndromes are less well known, probably due to a combination of milder, less distinct phenotype which may be unrecognized as a particular syndrome, and the difficulty of detecting microduplications compared to microdeletions.

The classic case of reciprocal microdeletion/micro-duplication syndromes is that of the peripheral neuropathies of 17p12.[2] Deletion of a 1.5-Mb segment results in ''hereditary neuropathy with liability to pressure palsies'' (HNPP), whereas duplication of the same region results in Charcot-Marie-Tooth disease Type 1A (CMT1A). The rearrangements involve the 24-kb CMT1A-REP repeats and the change in dosage of the central gene PMP22 is thought to cause the peripheral neuropathies typical of both disorders. Details of these syndromes are covered elsewhere. Below are reviewed other microduplication syndromes, which include interstitial duplications such as CMT1A, as well as duplication through the presence of a supernumerary chromosome. The phenotype associated with such microduplication syndromes presumably arises due to the overexpression of one or more genes in the duplicated regions.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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