Lactase Deficiency

Lactose intolerance (or hypolactasia) is the term used to describe a decline in the level of lactase, an enzyme needed for proper metabolization of lactose (a sugar that is a constituent of milk and other dairy products), in human beings. Although an estimated 70% of adult humans are considered lactose intolerant, it is uncommon in healthy northern westerners and a few others groups.
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Lactase deficiency /lac·tase de·fi·cien·cy/ reduced or absent lactase activity in the intestinal mucosa; the hereditary adult form is the normal [more]Lactase deficiency - Community and Resources

Noun
1. congenital disorder consisting of an inability to digest milk and milk products; absence or deficiency of lactase results in an inability to hydrolyze lactose
(synonym) lactose intolerance, milk intolerance
(hypernym) genetic disease, genetic disorder, genetic abnormality, genetic defect, congenital disease, inherited disease, inherited disorder, hereditary disease, hereditary condition

Lack of the enzyme lactase resulting in failure to digest lactose in milk (lactose intolerance).