Sotos syndrome (OMIM #117550) is a congenital syndrome characterized by 
overgrowth with advanced bone age, macrocephaly, and learning difficulties. 
Endocrine complications of this syndrome have not yet been fully described in 
previous reports. We here investigated the clinical manifestations of Sotos 
syndrome in Japanese patients who presented with hyperinsulinemic hypoglycemia 
of infancy. We recruited patients diagnosed as having Sotos syndrome who 
presented with the complication of hyperinsulinemia during the neonatal period 
using a survey of the abstracts of Pediatric Meetings in domestic areas of Japan 
from 2007 to 2011. As a result, five patients (four females and one male) were 
recruited to evaluate the clinical presentation of Sotos syndrome by reference 
to the clinical record of each patient. A 5q35 deletion including the NSD1 gene 
was detected in all patients. Major anomalies in the central nervous, 
cardiovascular, and genito-urinary systems were frequently found. Hypoglycemia 
occurred between 0.5 and 3 hr after birth and high levels of insulin were 
initially found within 3 days of birth. The patients were treated with 
intravenous glucose infusion at a maximum rate of 4.6-11.0 mg/kg/min for 12-49 
days. Three of the five patients required nasal tube feeding. One patient 
received medical treatment with diazoxide. This study shows that patients with 
Sotos syndrome may present with transient hyperinsulinemic hypoglycemia in the 
neonatal period.