is a condition characterized by a distinctive facial appearance, overgrowth in childhood, and learning disabilities or delayed development. Affected individuals have facial features, most prominant in childhood, that include a long, narrow face; a high forehead; flushed (reddened) cheeks; and a small, pointed chin. In addition, the outside corners of the eyes may point downward (down-slanting palpebral fissures). Affected infants and children tend to grow quickly; they are significantly taller than their siblings and peers and have an unusually large head. People with Sotos syndrome often have intellectual impairment, and most also have behavioral problems. Problems with speech and language are also common. Additionally, weak muscle tone (hypotonia) may delay other aspects of early development, particularly motor skills such as sitting and crawling. Sotos syndrome is caused by mutations in the NSD1 gene. About 95% of cases represent new mutations and occur in families with no history of the condition. In a small number of families, the condition appears to be inherited in an autosomal dominant pattern. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.