The evolutionary genetics of lactase persistence in seven ethnic groups across the Iranian plateau

Hadi Charati,Roghayeh Jabbari Ori,Ali Esmailizadeh,Xing-Yan Yang,Ya-Ping Zhang,Min-Sheng Peng,Mohsen Aghajanpour-Mir,Wei Chen

doi:10.1186/s40246-019-0195-5

Abstract

BackgroundThe ability to digest dietary lactose is associated with lactase persistence (LP) in the intestinal lumen in human. The genetic basis of LP has been investigated in many populations in the world. Iran has a long history of pastoralism and the daily consumption of dairy products; thus, we aim to assess how LP has evolved in the Iranian population. We recruited 400 adult individuals from seven Iranian ethnic groups, from whom we investigated their lactose tolerance and screened the genetic variants in their lactase gene locus.ResultsThe LP frequency distribution ranged from 0 to 29.9% in the seven Iranian ethnic groups with an average value of 9.8%. The variants, − 13910*T and − 22018*A, were significantly associated with LP phenotype in Iranians. We found no evidence of hard selective sweep for − 13910*T and − 22018*A in Persians, the largest ethnic group of Iran. The extremely low frequency of − 13915*G in the Iranian population challenged the view that LP distribution in Iran resulted from the demic diffusion, especially mediated by the spread of Islam, from the Arabian Peninsula.ConclusionsOur results indicate the distribution of LP in seven ethnic groups across the Iranian plateau. Soft selective sweep rather than hard selective sweep played a substantial role in the evolution of LP in Iranian populations.

Highlights

The ability to digest dietary lactose is associated with lactase persistence (LP) in the intestinal lumen in human
The lactase status was classified into three categories on the basis of the maximum rise in glucose level: an individual with a blood glucose level > 1.7 mmol/L was classified as LP; an individual with a blood glucose level < 1.1 mmol/L was classified as lactase non-persistence (LNP); and “lactase intermediate persistent” (LIP) was classified as an individual with a blood glucose level between 1.1 and 1.7 mmol/L
LP in the Iranian populations According to the lactose tolerance test (LTT) results, LP, LIP, and LNP accounted for 9.5%, 24%, and 66.5% of the total Iranian studied population, respectively (Table 1)

Summary

Introduction

The ability to digest dietary lactose is associated with lactase persistence (LP) in the intestinal lumen in human. Iran has a long history of pastoralism and the daily consumption of dairy products; we aim to assess how LP has evolved in the Iranian population. We recruited 400 adult individuals from seven Iranian ethnic groups, from whom we investigated their lactose tolerance and screened the genetic variants in their lactase gene locus. Lactase persistence (LP; OMIM #223100) is defined as the continued lactase enzyme activity that helps to digest lactose in dairy products in human adulthood [1]. It follows a Mendelian autosomal heritance [2] regulated by cis-acting elements of the lactase gene (LCT; OMIM *603202) [3]. We sequenced the relevant genomic region to identify potential variants that are associated with LP

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