Aform of hypoglycemia, or low blood- sugar level, that occasionally runs in families.Children who are afflicted with this disorder not only show the usual hypoglycemic symptoms of weakness, fatigability, apathy, and occasional seizures, but also fail to develop intellectually. It is therefore included among the causes of mental retardation associated with faulty metabolism. The term idiopathic refers to the fact that the hypoglycemia cannot be traced to another disorder. It is believed to be due to a single recessive gene.