The T/G 13915 variant upstream of the lactase gene (LCT) is the founder allele of lactase persistence in an urban Saudi population.

BACKGROUND: The prevalence of lactase persistence is high in Saudi Arabia. OBJECTIVE: To identify a DNA variant for the lactase persistence/non-persistence trait in adult Arabs in Saudi Arabia. METHODS: We sequenced DNA from 432 anonymous neonatal blood donors from five different regions of Saudi Arabia to cover the 400 bp region surrounding the previously identified lactase persistence/non-persistence variant C/T-13910 residing in intron 13 of the MCM6 gene. RESULTS: Two anonymous blood donors carried the C/T-13910 genotype. One variant, T/G -13915, residing 5 bp upstream of the C/T-13910 variant, was present in 332 of 432 (76.9%) of the neonatal samples, compatible with previous prevalence figures of lactase persistence in urban Saudi populations. Determination of disaccharidase activities in 25 intestinal biopsy samples showed a highly significant correlation between lactase activity and the T/G-13915 genotypes (p<0.001; Fisher exact test) as well as between the L:S ratio and the aforementioned genotypes (p<0.001; Fisher exact test). CONCLUSION: The T/G-13915 variant is the founder mutation of lactase persistence in an urban Saudi population. The results obtained here have implications for genetic testing of adult-type hypolactasia and to analysis of human evolution, the origin of cattle domestication and migrations of the populations in the Arabian peninsula.

Functional analysis of tumour necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL): cysteine-230 plays a critical role in the homotrimerization and biological activity of this novel tumoricidal cytokine.

We have determined that the mutation of the cysteine-230 residue to either glycine or serine in TRAIL (tumour necrosis factor-alpha-related apoptosis-inducing ligand) results in the formation of a structurally incompetent dimer and a consequent loss of apoptotic activity. Similarly, chemical modification of the thiol residues present in both reduced and Zn(2+)-depleted trimer converts TRAIL into an inactive dimer. We postulate that cysteine-230 plays a critical role in homotrimerization of this tumoricidal cytokine.