Genetically programmed down-regulation of the lactase gene (adult-type hypolactasia) is detectable in children from the second year of life, although the onset and extent are somewhat variable . The colonic micro flora ferments undigested lactose in the intestinal lumen, producing hydrogen, carbon dioxide and methane, provoking gastrointestinal symptoms characterized by bloating, flatulence, abdominal pain and diarrhea .
Lactase non-persistence is the most common phenotype in humans, with frequencies around 65%, except in northwestern Europe with its long history of pastoralism and milking . Enattah et al. (2002) identified a variant allele polymorphism LCT -13910C>T upstream from the lactase gene locus, associated with hypolactasia/lactase persistence in Finland and elsewhere ; an exception is Africa, with three identified single nucleotide polymorphisms: LCT -14010G>C, LCT -13915T>G, and LCT -13907C>G .
The DNA region of the LCT -13910C>T lactase persistence-non persistence variant functioned in vitro as a cis regulatory element capable of enhancing differential transcriptional activation of the lactase promoter that is consistent with a causative role in the mechanism of lactase persistence/non-persistence phenotypes in humans .
The LCT -13910C>T polymorphism has been associated with adult-type hypolactasia in Brazilians ; thus, we assessed its frequency among different Brazilian ethnic groups.