Genetics of Lactose Intolerance: An Updated Review and Online Interactive World Maps of Phenotype and Genotype Frequencies.

Augusto Anguita-Ruiz,Concepción M Aguilera,Ángel Gil

doi:10.3390/nu12092689

Abstract

In humans the ability to digest milk lactose is conferred by a β-galactosidase enzyme called lactase-phlorizin hydrolase (LPH). While in some humans (approximately two-thirds of humankind) the levels of this enzyme decline drastically after the weaning phase (a trait known as lactase non-persistence (LNP)), some other individuals are capable of maintaining high levels of LPH lifelong (lactase persistence (LP)), thus being able to digest milk during adulthood. Both lactase phenotypes in humans present a complex genetic basis and have been widely investigated during the last decades. The distribution of lactase phenotypes and their associated single nucleotide polymorphisms (SNPs) across human populations has also been extensively studied, though not recently reviewed. All available information has always been presented in the form of static world maps or large dimension tables, so that it would benefit from the newly available visualization tools, such as interactive world maps. Taking all this into consideration, the aims of the present review were: (1) to gather and summarize all available information on LNP and LP genetic mechanisms and evolutionary adaptation theories, and (2) to create online interactive world maps, including all LP phenotype and genotype frequency data reported to date. As a result, we have created two online interactive resources, which constitute an upgrade over previously published static world maps, and allow users a personalized data exploration, while at the same time accessing complete reports by population or ethnicity.

Highlights

Lactose is the main carbohydrate present in milk and one of the main sources of energy during the nursing period in mammals
The ability to digest milk lactose is conferred by a β-galactosidase enzyme called lactase-phlorizin hydrolase (LPH) [2,3]
The hydrolysis of milk lactose in the intestine is catalyzed by the enzyme lactase-phlorizin hydrolase (LPH) (EC 3.2.1.108–EC 3.2.1.62), a β-galactosidase located in the brush border membrane of small-intestinal enterocytes

Summary

Introduction

Lactose is the main carbohydrate present in milk and one of the main sources of energy during the nursing period in mammals. The ability to digest milk lactose is conferred by a β-galactosidase enzyme called lactase-phlorizin hydrolase (LPH) [2,3]. The LPH enzyme is encoded by the lactase (LCT) gene, located on the chromosome 2q21. Expressed in the small intestine, in the apical part of microvilli within the brush border membrane of enterocytes, the LPH enzyme reaches the highest levels of activity during the nursing period [4]. In the majority of humans, the activity of LPH declines rapidly because of a decrease in the levels of the enzyme, and this trait is known as Nutrients 2020, 12, 2689; doi:10.3390/nu12092689 www.mdpi.com/journal/nutrients

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