is a developmental disorder that affects many parts of the body. The major features of this condition include mild to moderate intellectual disability, delayed speech and language skills, distinctive facial features, sleep disturbances, and behavioral problems. Most people with Smith-Magenis syndrome have a deletion of genetic material from a specific region of chromosome 17. Although this region contains multiple genes, researchers believe that the loss of one particular gene, RAI1, in each cell is responsible for most of the characteristic features of the condition. Smith-Magenis syndrome is not typically inherited, but results from a genetic change that occurs during the formation of reproductive cells (eggs or sperm) or in early fetal development. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.