[Congenital lactase deficiency--a more common disease than previously thought?].

Congenital lactase deficiency belongs to the Finnish Disease Heritage and is a recessively inherited diarrheal disease of the newborn, in which the activity of the lactase enzyme of the epithelial cells of the small intestine is very low ever since the birth. For the newborn infant, ingestion of lactose causes symptoms so severe that breastfeeding is not possible. Untreated disease leads to dehydration that usually requires hospitalization. Congenital lactase deficiency is caused by mutations in the gene coding for the lactase enzyme (LCT). Seven mutations in a total of 43 patients have been found in Finland so far.