Defects in LCT are the cause of congenital lactase deficiency (COLACD) [MIM:223000]; also known as hereditary alactasia or disaccharide intolerance II. Congenital lactase deficiency is a an autosomal recessive, rare and severe gastrointestinal disorder. It is characterized by watery diarrhea in infants fed with breast milk or other lactose-containing formulas. An almost total lack of LCT activity is found in jejunal biopsy material of patients with congenital lactase deficiency. Opposite to congenital lactase deficiency, adult-type hypolactasia, also known as lactose intolerance, is the most common enzyme deficiency worldwide. It is caused by developmental down-regulation of lactase activity during childhood or early adulthood. The decline of lactase activity is a normal physiological phenomenon; however, the majority of Northern Europeans have the ability to maintain lactase activity and digest lactose throughout life (lactase persistence). The down-regulation of lactase activity operates at the transcriptional level and it is associated with a noncoding variation in the MCM6 gene, located in the upstream vicinity of LCT.
Belongs to the glycosyl hydrolase 1 family.
The sequence exhibits 4 regions (I-IV) of internal homology; therefore LPH might have evolved by two cycles of partial gene duplication.