Haploinsufficiency of the NSD1 gene due to 5q35 microdeletions or intragenic 
mutations is the major cause of Sotos syndrome characterized by generalized 
overgrowth, large hands and feet with advanced bone age, craniofacial dysmorphic 
features, learning disability, and possible susceptibility to tumors. Here, we 
report on a 14-month-old boy with a reverse phenotype of Sotos syndrome due to 
the reciprocal duplication of the 5q35.3 region, including the NSD1 gene, 
detected by array CGH. The phenotype includes delayed bone age, microcephaly, 
seizures, and failure to thrive. Our case suggests that the gene dosage effect 
of the NSD1 gene is the likely cause for the reversed phenotype of Sotos 
syndrome in this patient.