What causes lactase deficiency and what are the clinical manifestations?

• A. Lactase enzyme deficiency; lactose malabsorption leads to bloating, flatulence, osmotic diarrhea after dairy ingestion.
• B. Amylase deficiency causing hypoglycemia.
• C. Excess lactase production causing diarrhea after bread.
• D. Hypersecretion of bile causing steatorrhea.

Answer: (A)

Lactase deficiency happens when the enzyme lactase in the small-intestinal lining is deficient or absent, so lactose from dairy isn’t properly digested into glucose and galactose. This lactose then stays in the gut lumen, pulling water into the intestine (osmotic effect) and being fermented by colonic bacteria, which produces gas and irritates the bowel. The result is symptoms that reliably follow dairy intake: bloating, abdominal cramps or pain, flatulence, and osmotic diarrhea.

In real life, this can occur as a normal, age-related decline in lactase production (primary lactase non-persistence) that many adults develop, or it can be congenital and rare. It can also be secondary to damage of the intestinal lining from conditions like celiac disease or gastroenteritis, which temporarily or permanently reduces lactase production.