Lactose intolerance is a common malabsorption disease caused by insufficient lactase enzyme in the small intestine resulting in flatulence, diarrhea, bloating, and cramping abdominal pain after ingesting lactose-containing foods. The incidence of lactose intolerance varies among ethnicities, with patients of African, Asian, Native American, and Hispanic descent most affected.
Lactase deficiency can be primary, secondary, or congenital.
Primary – Low levels of lactase enzyme. Symptom onset may be in childhood or adulthood.
Secondary – Reversible lactase deficiency caused by mucosal injury, often in the setting of viral illnesses.
Congenital – A rare autosomal recessive absence of lactase activity at birth leading to diarrhea and hypercalcemia in infancy, predisposing patients to nephrocalcinosis.