Adult-type hypolactasia (ATH), also known as lactase non-persistence or lactose intolerance (LI), is a clinical syndrome of primary lactase deficiency with one or more of the following: abdominal pain, diarrhea, nausea, flatulence, and bloating after the ingestion of lactose or lactose-containing food. The gene discussed is LCT; the disease is lactose intolerance.