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. 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. 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. 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.
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A Guide to Natural Sleep Remedies. Many of us experience the occasional night of sleeplessness without any consequences. It is when the occasional night here and there becomes a pattern of several nights in arow that you are faced with a sleeping problem. Repeated loss of sleep affects all areas of your life The physical, the mental, and theemotional. Sleep deprivation can affect your overall daily performance and may even havean effecton your personality.