Rare diseases · Sign or symptom
Decreased small intestinal mucosa lactase level
HP:0025130
What it means
Lactase is produced in the small intestine in humans, Lactase is a member of the beta-galactosidase family of enzymes, and hydrolyzes D-lactose to form D-galactose and D-glucose, which can be absorbed by the small intestine. There are many ways of assessing lactase activity. In one test, an endoscopic biopsy from the postbulbar duodenum is incubated with lactose on a test plate, and a color reaction develops within 20 min as a result of hydrolyzed lactose (a positive result) in patients with normolactasia, whereas no reaction (a negative result) develops in patients with severe hypolactasia. Other, less direct, tests include the hydrogen breath test, and blood tests following lactose challenges.
In everyday care
Most people with this sign do not have a rare disease — it appears in common conditions far more often. These general reference pages cover the same topic:
Rare diseases that can present with this1
The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Also called: Lactase deficiency
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Start free with EleplanThis page uses the Human Phenotype Ontology (2026-06-23) — Human Phenotype Ontology Consortium, hpo.jax.org. Disease associations from Orphanet (INSERM), CC BY 4.0. Content is educational and is not medical advice.