World-wide distributions of lactase persistence alleles and the complex effects of recombination and selection.

The genetic trait of lactase persistence (LP) is associated with at least five independent functional single nucleotide variants in a regulatory region about 14 kb upstream of the lactase gene [-13910*T (rs4988235), -13907*G (rs41525747), -13915*G (rs41380347), -14009*G (rs869051967) and -14010*C (rs145946881)]. These alleles have been inferred to have spread recently and present-day frequencies have been attributed to positive selection for the ability of adult humans to digest lactose without risk of symptoms of lactose intolerance. One of the inferential approaches used to estimate the level of past selection has been to determine the extent of haplotype homozygosity (EHH) of the sequence surrounding the SNP of interest.

In Vitro Functional Analyses of Infrequent Nucleotide Variants in the Lactase Enhancer Reveal Different Molecular Routes to Increased Lactase Promoter Activity and Lactase Persistence.

The genetic trait that allows intestinal lactase to persist into adulthood in some 35% of humans worldwide operates at the level of transcription, the effect being caused by cis-acting nucleotide changes upstream of the lactase gene (LCT). A single nucleotide substitution, -13910 C>T, the first causal variant to be identified, accounts for lactase persistence over most of Europe. Located in a region shown to have enhancer function in vitro, it causes increased activity of the LCT promoter in Caco-2 cells, and altered transcription factor binding.

Diversity of lactase persistence in African milk drinkers.

The genetic trait of lactase persistence is attributable to allelic variants in an enhancer region upstream of the lactase gene, LCT. To date, five different functional alleles, -13910*T, -13907*G, -13915*G, -14009*G and -14010*C, have been identified. The co-occurrence of several of these alleles in Ethiopian lactose digesters leads to a pattern of sequence diversity characteristic of a 'soft selective sweep'.

Diversity of lactase persistence alleles in Ethiopia: signature of a soft selective sweep.

The persistent expression of lactase into adulthood in humans is a recent genetic adaptation that allows the consumption of milk from other mammals after weaning. In Europe, a single allele (-13910(∗)T, rs4988235) in an upstream region that acts as an enhancer to the expression of the lactase gene LCT is responsible for lactase persistence and appears to have been under strong directional selection in the last 5,000 years, evidenced by the widespread occurrence of this allele on an extended haplotype. In Africa and the Middle East, the situation is more complicated and at least three other alleles (-13907(∗)G, rs41525747; -13915(∗)G, rs41380347; -14010(∗)C, rs145946881) in the same LCT enhancer region can cause continued lactase expression.

The impact of cis-acting polymorphisms on the human phenotype.

Cis-acting polymorphisms that affect gene expression are now known to be frequent, although the extent and mechanisms by which such variation affects the human phenotype are, as yet, only poorly understood. Key signatures of cis-acting variation are differences in gene expression that are tightly associated with regulatory SNPs or expression Quantitative Trait Loci (eQTL) and an imbalance of allelic expression (AEI) in heterozygous samples. Such cis-acting sequence differences appear often to have been under selection within and between populations and are also thought to be important in speciation.

A worldwide correlation of lactase persistence phenotype and genotypes.

Background: The ability of adult humans to digest the milk sugar lactose - lactase persistence - is a dominant Mendelian trait that has been a subject of extensive genetic, medical and evolutionary research. Lactase persistence is common in people of European ancestry as well as some African, Middle Eastern and Southern Asian groups, but is rare or absent elsewhere in the world. The recent identification of independent nucleotide changes that are strongly associated with lactase persistence in different populations worldwide has led to the possibility of genetic tests for the trait.

Limitations of the murine nose in the development of nonviral airway gene transfer.

A clinical program to assess whether lipid GL67A-mediated gene transfer can ameliorate cystic fibrosis (CF) lung disease is currently being undertaken by the UK CF Gene Therapy Consortium. We have evaluated GL67A gene transfer to the murine nasal epithelium of wild-type and CF knockout mice to assess this tissue as a test site for gene transfer agents. The plasmids used were regulated by either (1) the commonly used short-acting cytomegalovirus promoter/enhancer or (2) the ubiquitin C promoter.