LCT‐22018G>A single nucleotide polymorphism is a better predictor of adult‐type hypolactasia/lactase persistence in Japanese‐Brazilians than LCT‐13910C>T

Adult type hypolactasia, the genetically programmed down-regulation of lactase enzyme activity in the intestinal wall after weaning, is a common condition worldwide, except for in northwestern Europe, where the prevalence is less than 10%. Lactose intolerant individuals complain of abdominal cramps, bloating, distention, flatulence and diarrhea after milk or lactose-containing food ingestion. The diagnosis of adult-type hypolactasia can be achieved by a hydrogen breath test that is cumbersome and provokes symptoms, or more recently, using a genetic approach. Lactase persistence and adult-type hypolactasia have been associated with the LCT-13910C.T and LCT -22018G.A polymorphisms in introns 13 and 9, respectively, of the minichromosome maintenance type 6 gene (MCM6) upstream of the LCT locus in several populations. In Brazil, the lactase persistence allele, LCT-13910T, was found in approximately 43% of both white (European descent) and brown (European and African descent), and 20% of black (African descent) Brazilians, but was absent in all Japanese-Brazilians studied. Recent epidemiological data regarding lactose intolerance/hypolactasia are lacking in Japan. This lack of information may be because of the relative rarity of symptoms; it has been shown that, although 92% of tested subjects were lactase deficient, only 2% were milk intolerant and 13% were lactose intolerant. Recent evidence in northern China suggests that LCT22018G.A, rather than LCT-13910C.T, LCT-13907C.G, LCT-13915T.G, or LCT-14010G.C, matched the lactase persistence phenotype. Therefore, the purpose of this study was to ascertain whether LCT-22018G.A would also be a predictor of lactase persistence in Japanese-Brazilians.