lack of an enzyme made by the small intestine called lactase, which prevents the body from digesting lactose (a sugar found in milk and milk products) properly.
lack of the lactase enzyme.
Not enough of an enzyme called lactase in the small intestine to digest lactose, a prominent component of milk and most other dairy products. Lactose is sometimes also used as an ingredient in other foods, so anyone with lactase deficiency should check food labels with care. See the entire definition of Lactase deficiency
Lack of adequate supply of enzyme LACTASE. People with lactase deficiency have difficulty digesting milk and milk products.