Lactase Persistence in Southern Iberia and Northwestern Africa: New Insights into the Population Structure and History of the Western Mediterranean

Abstract

The development of lactose tolerance in humans represents a fair example of interaction between biology and culture. Lactase persistence (LP) during adulthood is strongly associated with several genetic variants (SNPs) in the MCM6 region (2q21.3). The −13910 C/T is the most widely analysed variant in present-day human populations and its origin has been postulated in central Europe during the Neolithic. To deepen the knowledge on the incidence of LP trait in the western Mediterranean, a number of 470 adult individuals autochthonous from southern Iberia and north-western Africa (Mo- rocco) were genotyped for the SNPs −13907 C/G, −13910 C/T, −13915 T/G, and −14010 G/C related to LP phenotype. Allele and genotype frequencies were estimated as well as proportions of predicted LP phenotype. Besides, contour maps based on allele frequencies were constructed, and a Bayesian Model was implemented in order to analyse the geographic distribu- tion patterns of LP trait and associated mutations across Europe, Africa, Mediterranean Basin and neighbouring areas. Frequencies of the European −13910*T derived allele among southern Iberian populations reached a mean value of 0.418 whereas in Moroccan Berbers figures were comparatively lower: 0.092 (Bouhria), 0.175 (Figuig) and 0.188 (Asni). The −13915*G variant, with a probable origin in the Arabian Peninsula, was observed in the study of Moroccan Berber samples (not in the Iberia Peninsula) with frequencies varying between 0.025 (Asni) and 0.066 (Bouhria). The Bayesian model provided a frequency value for LP trait in the Iberian Peninsula of 0.615 (95% PI: 0.594 – 0.636) whereas in the Maghreb it was 0.313 (95% PI: 0.275 – 0.352). Our results give further support to an European origin for −13910*T allele, and unveils a negative gradient of its frequencies from Iberia towards Maghreb, giving evidence again to the recurrent prehistoric and historical human movements and admixture processes through the Gibraltar Strait and its adjacent coasts.