The cause of Beckwith-Wiedemann syndrome is unknown, but it appears to be genetic. Some cases may be associated with a defect in chromosome number 11. Affected children are often large at birth. Many have an abdominal wall defect, such as an umbilical hernia or omphalocele. They have a characteristic facial appearance with a gaping mouth and large tongue. Infancy can be a critical period because of low blood sugar (hypoglycemia), omphalocele (when present), and an increased rate of tumor development (Wilm's tumor and adrenal carcinoma being most common).
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