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 1. 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 2.

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 3. 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 4; an exception is Africa, with three identified single nucleotide polymorphisms: LCT -14010G>C, LCT -13915T>G, and LCT -13907C>G 5.

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 6.

The LCT -13910C>T polymorphism has been associated with adult-type hypolactasia in Brazilians 7; thus, we assessed its frequency among different Brazilian ethnic groups.

The local Ethics Committee approved this study. Randomly selected asymptomatic and dyspeptic individuals were invited to participate and gave written informed consent. Most symptomatic participants did not associate their symptoms with milk consumption. Ethnic groups were classified according to ethnicity as White, Brown (of White and African-Brazilian descent), Black, and Japanese-Brazilian. A total of 567 individuals were included [mean age, 42.1 ± 16.8 years; 157 (27.7%) men]; 399 (70.4%) White, 50 (8.8%) Black, 65 (11.5%) Brown, and 53 (9.3%) Japanese-Brazilian.

Among the 567 individuals, the prevalence of LCT-13910CC genotype varied among ethnic groups. The White and Brown groups had the same prevalence (~57%); Black individuals had prevalence of 80%; and among Japanese-Brazilians, the prevalence was 100%. Only 2 (4%) Blacks had LCT-13910TT genotype, and 8 (16%) had the CT genotype. The White and Brown groups had similar LCT-13910CT genotype prevalence (37.3% and 40%, respectively). The rare LCT-13910TT genotype (4.9%, 28/567) occurred more frequently in the White group (6%, 24/399) than the Brown (3.1%, 2/65) (Table 1). Gender and allele frequencies showed no association.

Assuming an association between LCT-13910CC genotype and hypolactasia, and LCT-13910CT and TT genotypes with lactase persistence, 356 (62.8%) individuals had hypolactasia and 211 (37.2%) had lactase persistence. The White and Brown groups had the same hypolactasia prevalence (~57%); nonetheless, Black individuals and Japanese-Brazilians had 80% and 100%, respectively (P < 0.01) (Table 1).

The multi-ethnic Brazilian population includes descendents of Europeans, Amerindians (native population at the European arrival in 1500), and Africans brought as slaves from 1550-1800. Mitochondrial DNA analysis indicates that African-Brazilians carry the relative ancestral contribution of central-west, southeast, and west Africa 10, where the LCT-13910T variant of lactase persistence of Europeans in Africa was present 5. Black-Brazilians have the LCT-13910T variant of lactase persistence although at a low frequency. However, most likely the LCT-13910T allele of European origin is the outcome of genetic admixture, a consequence of extensive interbreeding with Europeans that occurred through the centuries 10.

Brown and White individuals followed the same pattern of allelic frequencies. Interestingly, all Japanese-Brazilians had LCT-13910CC genotype, suggesting very low interbreeding between Japanese-Brazilian and European-Brazilian groups; nonetheless, these values agree with previous results of lactose malabsorption in White, and Black Brazilians and those of Japanese descent 11.

We conclude that the lactase persistence allele, LCT -13910T, was found in about 43% of both White and Brown and 20% of the Black Brazilians, but was absent among all Japanese- Brazilians studied.

The authors declare that they have no competing interests.

RM participated in the conception, design, analysis and interpretation of data, performed the statistical analysis, manuscript preparation and revision; MSM, CAV, AFS, JMKS carried out the molecular genetic studies and acquisition of data; FJC gave final approval of the version to be published. All authors read and approved the final manuscript.