Partial or complete deficiency of the enzyme lactase in the small intestine, resulting in an inability to digest the sugar lactose in milk, and hence intolerance of milk.
A condition in which there is a deficiency of lactase in the intestine, making the patient incapable of digesting lactose, the sugar in milk.
Absence or deficiency of the enzyme lactase, which is essential for the digestion of milk sugar (lactose). All babies have lactase in their intestines, but the enzyme disappears during childhood in about 10% of northern Europeans, 40% of Greeks and Italians, and 80% of Africans and Asians. Alactasia causes symptoms only if the diet regularly includes raw milk, when the undigested lactose causes diarrhea and abdominal pain.