Thomas, Shanthi; (1990) Lactase restriction and lactase persistence: a study of sri lankans and a paediatric population. Doctoral thesis (M.D), University of London, Institute of Child Health.

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Abstract

Lactase is an enzyme, located on the small intestinal brush border, that hydrolyses the disaccharide lactose into its monosaccharides glucose and galactose, which are then absorbed. In mammals the enzyme is present at birth and disappears after weaning. In all human neonates the enzyme is also present at birth. In the majority of the world population the enzyme activity declines during childhood (lactase restriction phenotype) and only in a minority does the enzyme activity persist in adults (lactase persistence phenotype). It is most likely that genetic and environmental factors are involved in determining these phenotypes. All the evidence suggests that lactase persistence is a result of genetic mutation conferring a selective advantage among some populations. The enzyme lactase has been characterised and cloned, and the gene is located on Chromosome 2. There is some evidence that the molecular mechanism of the genetic expression of the phenotypes include post-transcriptional processing of the enzyme precursor. In this study, 291 oral lactose loads and lactase activities of 41 small intestinal biopsies have been used to investigate the progression and prevalence rate of the lactase phenotypes in Sri Lankans. A comparison was made by studying the lactase activities of 170 histologically normal small intestinal biopsies on British children of mixed ethnic origin. Lactase was present at birth in Sri Lankan children and declined around the age of eight years, the majority (73-95%) of the adults belonging to the lactase restriction phenotype. In contrast the majority of the British children belonged to the lactase persistence phenotype throughout childhood. The lactase restriction phenotype found among British children was largely contributed by children of Asian and African origin. Although most adult Sri Lankans demonstrated low intestinal lactase activities, this did not lead to any significant clinical problems. They did not suffer from clinical lactose intolerance or other related clinical complaints in the majority of the cases.

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