Lactase persistence phenotype and genotype in Iranian Mazani-Shahmirzadi and Afghan Hazara ethnicities

Lactase persistence is an autosomal dominant trait characterized by sustained expression of lactase gene throughout adulthood. This trait is mostly prevalent in populations with pastoral or agro-pastoral ancestry and allows lactase persistent individuals to benefit from milk nutrients. Several genetic variants have been identified to be responsible for lactase persistence in different populations and other genetic variants associated with lactase persistence are expected to be found. In this study, we aimed to investigate the lactase persistence phenotype and genotype in two isolated populations, the Iranian Mazani-Shahmirzadi and Afghan Hazaras living in Iran. For this purpose, we genotyped five single nucleotide polymorphisms -13.907C/G, -13.910C/T, -13.913T/C, -13.915T/G and -22.018A/G in 45 Mazanis from Shahmirzad and 50 Hazaras living in the suburb of Tehran. We also investigated lactase persistence by inquiring about digestive symptoms and measuring blood glucose levels after 50g lactose consumption. Our results show that 24.2% of Mazani-Shahmirzadis and 14% of Hazaras are lactase persistent based on blood glucose levels. Genotype investigation shows that only two SNPs, 13.910 C/T and 22.018 A/G display variation in the studied populations. The -13.910*T allele has a frequency of 7.7% in Mazani-Shahmirzadis and 12.7% in Hazaras. The frequency of -22.018*A was 16.6% in Mazani-Shahmirzadis and 17% in Hazaras. Importantly, we found a new genetic variant at -13.913 single nucleotide polymorphism which has not been previously reported. Given that the -13.913 single nucleotide polymorphism is within the enhancer Oct-1 binding site, the presence of this variant could affect lactase gene expression in adults. Further studies are required to elucidate the impact of this variant on LCT gene enhancer function.