A rare autosomal recessive disorder (OMIM:223000), characterised by severe watery diarrhoea in infants fed with breast milk or other lactose-containing milk formulas. A virtually complete lack of LCT activity is found in jejunal biopsy material.
In contrast, adult-type hypolactasia, aka lactose intolerance, the most common enzyme deficiency worldwide, is due to a developmental down-regulation of lactase activity which evolves from childhood to early adulthood, and is regarded as a normal physiological phenomenon. Most northern Europeans maintain lactase activity and digest lactose throughout life, a phenomenon known as lactase persistence.
Molecular pathology Defects of LCT, which encodes lactase, a glycosyl hydrolase, cause lactase deficiency—congenital.
Synonyms Alactasia—congenital, COLACD, disaccharide intolerance II, hereditary alactasia, lactase deficiency—congenital