Lactose Intolerance - Causes

Causes

Lactose intolerance is a consequence of lactase deficiency, which may be genetic or environmentally induced. In either case, symptoms are caused by insufficient levels of the enzyme lactase in the lining of the duodenum. Lactose, a disaccharide molecule found in milk and dairy products, cannot be directly absorbed through the wall of the small intestine into the bloodstream so, in the absence of lactase, passes intact into the colon. Bacteria in the colon are able to metabolise lactose, and the resulting fermentation produces copious amounts of gas (a mixture of hydrogen, carbon dioxide and methane) that causes the various abdominal symptoms. The unabsorbed sugars and fermentation products also raise the osmotic pressure of the colon, resulting in an increased flow of water into the bowels (diarrhea). Certain mutation in the LCT gene allow lactase continue to be expressed after stopping breast feeding. The LCT gene which encodes the lactase protein is located on the long arm (q) of chromosome 2 in region 21. The locus can be expressed as 2q21.