rs4988235

rs4988235, also known as LCT-13910C>T, is a regulatory SNP located about 14 kb upstream of the lactase (LCT) gene, sitting within an intron of the neighboring MCM6 gene in an enhancer element bound by transcription factor Oct-1. The T allele disrupts the normal postweaning shutdown of LCT transcription, keeping lactase enzyme expression high into adulthood (lactase persistence), whereas the ancestral C allele is linked to the typical decline in lactase after infancy and lactose intolerance; T/T and C/T genotypes digest dietary lactose markedly better than C/C. It is the marker used for lactose digestion, and is also included alongside FUT2 rs601338 as context for a secretor-status/gut-microbiome trait, since lactase-persistence genotype shapes gut microbial composition data independent of secretor status itself.