Lactose intolerance and lactase deficiency

Lactase deficiency exists in four distinct forms: primary (the most common), secondary, congenital, and developmental.

Treatment of primary lactase deficiency is indicated only when it manifests as a clinical syndrome of lactose intolerance.

Lactose intolerance is characterized by gastrointestinal symptoms such as diarrhea, bloating, and abdominal discomfort. Some patients have systemic symptoms (e.g., headache, poor short-term memory, severe tiredness, joint and/or muscle pain, atopic dermatitis, mouth ulceration)

Dietary elimination and challenge are generally diagnostic.

Treatment includes reduction or elimination of dietary lactose.

If elimination of lactose is necessary, alternative calcium sources are recommended.

Lactase deficiency is usually primary (hereditary) due to a nonpersistence of lactase with an age-related decline that begins after weaning although it is rare before 2-3 years of age. This results in hypolactasia (low lactase activity), characterized by reduced lactase (lactase-phlorizin hydrolase enzyme) concentration in the mucosal brush border (microvilli) of the small intestine.[1]Matthews SB, Waud JP, Roberts AG, et al. Systemic lactose intolerance: a new perspective on an old problem. Postgrad Med J. 2005 Mar;81(953):167-73. https://pmj.bmj.com/content/81/953/167.long http://www.ncbi.nlm.nih.gov/pubmed/15749792?tool=bestpractice.com [2]Heyman MB; American Academy of Pediatrics, Committee on Nutrition. Lactose intolerance in infants, children, and adolescents. Pediatrics. 2006 Sep;118(3):1279-86. http://pediatrics.aappublications.org/content/118/3/1279.long http://www.ncbi.nlm.nih.gov/pubmed/16951027?tool=bestpractice.com [3]Lomer ME, Parkes GC, Sanderson JD. Lactose intolerance in clinical practice - myths and realities. Aliment Pharmacol Ther. 2008 Jan 15;27(2):93-103. http://www.ncbi.nlm.nih.gov/pubmed/17956597?tool=bestpractice.com Less often, lactase deficiency is secondary to small bowel injury: causes include infection (e.g., HIV enteropathy, tropical sprue), systemic conditions (e.g., carcinoid syndrome), chemotherapy and radiation therapy. In infants lactase deficiency is most often secondary to infection (gastroenteritis) or cows’ milk protein allergy.

Congenital lactase deficiency is an extremely rare, lifelong disorder characterized by faltering growth and intractable diarrhea from the first exposure to breast or lactose-containing formula milk. Affected infants have minimal or absent lactase activity. Lactase deficiency is also seen in preterm infants due to the mucosal structure not being developed fully.

All forms of lactase deficiency lead to lactose malabsorption when the amount of lactose ingested is larger than the body’s ability to digest it due to low lactase activity. Malabsorption of lactose; however, does not always manifest as gastrointestinal symptoms.

Lactose intolerance refers to the development of gastrointestinal and/or systemic symptoms secondary to malabsorption of lactose caused by hypolactasia. Development of symptoms and symptom severity depend on the amount and rate of lactose reaching the colon, as well as the type and amount of colonic flora.[1]Matthews SB, Waud JP, Roberts AG, et al. Systemic lactose intolerance: a new perspective on an old problem. Postgrad Med J. 2005 Mar;81(953):167-73. https://pmj.bmj.com/content/81/953/167.long http://www.ncbi.nlm.nih.gov/pubmed/15749792?tool=bestpractice.com