Sotos syndrome is a genetic disorder characterized by a typical facial 
appearance, macrocephaly, accelerated growth, developmental delay, and a 
variable range of associated abnormalities. The NSD1 gene was recently found to 
be responsible for Sotos syndrome, and more than 150 patients with NSD1 
alterations have been identified. A significant ethnic difference is found in 
the prevalence of different types of mutation, with a high percentage of 
microdeletions identified in Japanese Sotos syndrome patients and with 
intragenic mutations in most non-Japanese patients. NSD1 aberrations are rather 
specific for Sotos syndrome, but have also been detected in patients lacking one 
or more major criteria of the disorder, namely overgrowth, macrocephaly, and 
advanced bone age. Thus, new diagnostic criteria should be considered. Studies 
have reported different frequencies of mutations versus non-mutations in Sotos 
syndrome, thus indicating allelic or locus hetereogeneity. Although some authors 
have suggested genotype/phenotype correlations, further studies are needed.