Duplications Of 17p112

Recombination between a set of low-copy repeats in 17p11.2 causes the microdeletion syndrome known as Smith-Magenis syndrome (SMS). This disorder, with an estimated prevalence of 1/20,000, is characterized by mental retardation, neurobehavioral abnormalities, sleep disorders, speech and motor delays, midface hypoplasia, short stature, and brachydactyly.[3] The same deletion is seen in 90% of patients. Only recently has it been recognized that a reciprocal duplication also exists. The dup(17)(p11.2p11.2) syndrome is characterized by borderline to mild mental retardation, behavioral problems, short stature, dental anomalies, normal facies, and lack of major organ malformations[4,5] This syndrome typifies a milder phenotype that was not recognized as a syndrome until connected to the microduplication.

Nonallelic homologous recombination is thought to occur between the 200-kb SMS-REPs, which are direct repeats separated by -4 Mb.[6] A third SMS-REP exists with the SMS region, but because of its inverted orientation it does not usually participate in deletion/ duplication formation. Interchromosomal and intrachro-mosomal exchanges appear to occur with equal frequency, as determined by microsatellite analysis of 16 dup(17)(p11.2p11.2) syndrome patients.[5] There appears to be no significant parent-of-origin bias among these 16 patients. The gene or genes involved in the dup(17)-(p11.2p11.2) syndrome are unknown. Recently, chromosome engineering in mice has resulted in mouse models for both deletion and duplication syndromes of the equivalent murine region of conserved synteny.[7]

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