Hunting for the LCT-13910*T allele between the Middle Neolithic and the Middle Ages suggests its absence in dairying LBK people entering the Kuyavia region in the 8th millennium BP.

Henryk W Witas,Tomasz Kozłowski,Krystyna Jędrychowska-Dańska,Alicja Masłowska,Blandyna Jerszyńska,Grzegorz Osipowicz,Piotr J Witas,Tomasz Płoszaj,Arnar Palsson

doi:10.1371/journal.pone.0122384

Abstract

Populations from two medieval sites in Central Poland, Stary Brześć Kujawski-4 (SBK-4) and Gruczno, represented high level of lactase persistence (LP) as followed by the LCT-13910*T allele’s presence (0.86 and 0.82, respectively). It was twice as high as in contemporaneous Cedynia (0.4) and Śródka (0.43), both located outside the region, higher than in modern inhabitants of Poland (0.51) and almost as high as in modern Swedish population (0.9). In an attempt to explain the observed differences its frequency changes in time were followed between the Middle Neolithic and the Late Middle Ages in successive dairying populations on a relatively small area (radius ∼60km) containing the two sites. The introduction of the T allele to Kuyavia 7.4 Ka BP by dairying LBK people is not likely, as suggested by the obtained data. It has not been found in any of Neolithic samples dated between 6.3 and 4.5 Ka BP. The identified frequency profile indicates that both the introduction and the beginning of selection could have taken place approx. 4 millennia after first LBK people arrived in the region, shifting the value of LP frequency from 0 to more than 0.8 during less than 130 generations. We hypothesize that the selection process of the T allele was rather rapid, starting just after its introduction into already milking populations and operated via high rates of fertility and mortality on children after weaning through life-threatening conditions, favoring lactose-tolerant individuals. Facing the lack of the T allele in people living on two great European Neolithization routes, the Danubian and Mediterranean ones, and based on its high frequency in northern Iberia, its presence in Scandinavia and estimated occurrence in Central Poland, we propose an alternative Northern Route of its spreading as very likely. None of the successfully identified nuclear alleles turned out to be deltaF508 CFTR.

Highlights

35% of adult people around the world digest lactose after weaning
Different from that of modern inhabitants of Poland (0.3) [33] was the distribution of the T allele in Stary Brześć Kujawski-4 (SBK-4) (P = 0.025, FST = 0.06) and Gruczno (P = 0.0002, FST = 0. 118), in contrast to values estimated for Cedynia (P = 0.163, FST = 0.012) and Śródka (P = 0.487, FST = 0.0008)
Having in mind high frequency of lactase persistence in people from medieval SBK-4 (0.86) and Gruczno sites (0.82), we determined the frequency of the T allele and LP in individuals from two small populations living in Rogowo and Linowo a millennium earlier, both representing the Roman

Summary

Introduction

35% of adult people around the world digest lactose after weaning. In most Europeans [1] the so-called lactase persistence/non-persistence (LP/L-nP) is associated with a single nucleotide polymorphism (SNP) C>T located 13910 bp upstream (rs4988235) from the start codon of lactase-phlorizin hydrolase (LPH), within intron 13 of MCM6 (minichromosome maintenance complex component 6) [1]. The employed model showed that the closer from the arrival time of LBK to the Hallstatt period, the more probable is the introduction of the T allele and participation of the selection process in its sustaining in population. That is, moving towards the present times from 7.4 Ka BP and allowing for non-zero selection coefficient one is able to increase the mentioned probability of the T allele introduction and selection from several to about 50%. Approaching too close to Hallstatt resulted in rather high selection coefficients, reaching the value of 0.06. To allow for a wide range of values and significant probability of scenarios (probability >30%) one obtains a lower bound for the T allele introduction time equal to approx.145 generations after the arrival of LBK people (Fig. 2A).

Methods

Results

Conclusion