Positive selection of lactase persistence among people of Southern Arabia.

OBJECTIVE: Frequency patterns of the lactase persistence (LP)-associated -13,915 G allele and archaeological records pointing to substantial role played by southern regions in the peopling and domestication processes that involved the Arabian Peninsula suggest that Southern Arabia plausibly represented the center of diffusion of such adaptive variant. Nevertheless, a well-defined scenario for evolution of Arabian LP is still to be elucidated and the burgeoning archaeological picture of complex human migrations occurred through the peninsula is not matched by an equivalent high-resolution description of genetic variation underlying this adaptive trait. To fill this gap, we investigated diversity at a wide genomic interval surrounding the LCT gene in different Southern Arabian populations. METHODS: 40 SNPs were genotyped to characterize LCT profiles of 630 Omani and Yemeni individuals to perform population structure, linkage disequilibrium, population differentiation-based and haplotype-based analyses. RESULTS: Typical Arabian LP-related variation was found in Dhofaris and Yemenis, being characterized by private haplotypes carrying the -13,915 G allele, unusual differentiation with respect to northern groups and conserved homozygous haplotype-blocks, suggesting that the adaptive allele was likely introduced in the Arabian gene pool in southern populations and was then subjected to prolonged selective pressure. CONCLUSION: By pointing to Yemen as one of the best candidate centers of diffusion of the Arabian-specific adaptive variant, obtained results indicate the spread of indigenous groups as the main process underlying dispersal of LP along the Arabian Peninsula, supporting a refugia model for Arabian demic movements occurred during the Terminal Pleistocene and Early Holocene.

The Phenotype/Genotype Correlation of Lactase Persistence among Omani Adults.

OBJECTIVE: To examine the correlation of lactase persistence phenotype with genotype in Omani adults. METHODS: Lactase persistence phenotype was tested by hydrogen breath test in 52 Omani Adults using the Micro H2 analyzer. Results were checked against genotyping using direct DNA sequencing. RESULTS: Forty one individuals with C/C-13910 and T/T-13915 genotypes had positive breath tests (≥20 ppm); while eight of nine individuals with T/C-13910 or T/G-13915 genotypes had negative breath tests (<20 ppm) and two subjects were non-hydrogen producers. The agreement between phenotype and genotype using Kappa value was very good (0.93). CONCLUSION: Genotyping both T/C-13910 and T/G-13915 alleles can be used to assist diagnosis and predict lactose intolerance in the Omani population.

First case report of familial hypercholesterolemia in an Omani family due to novel mutation in the low-density lipoprotein receptor gene.

Familial hypercholesterolemia (FH) is an autosomal dominant genetic disorder. Mutations have been found in at least 3 genes: the low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), and proprotein convertase subtilisin/kexin type 9 (PCSK9). We report the first case of FH in an Omani family due to a novel mutation in the LDLR gene. A 9-year-old female was referred to our lipid clinic with eye xanthelasmata and thickening of both Achilles tendons. Evaluation of the lipid profile showed the off treatment total cholesterol of 896 mg/dL (23.2 mmol/L), low-density lipoprotein cholesterol (LDL-C) of 853 mg/dL (22.1 mmol/L), APOB of 4.5 g/L, triglyceride of 71 mg/dL (0.8 mmol/L), and high-density lipoprotein cholesterol of 0.74 mmol/L. Genetic analysis of the LDLR gene showed a homozygous frameshift deletion mutation (272delG) at exon 3. The female patient was treated with a combination of rosuvastatin/ezetimibe and LDL apheresis.

Pleistocene-Holocene boundary in Southern Arabia from the perspective of human mtDNA variation.

It is now known that several population movements have taken place at different times throughout southern Arabian prehistory. One of the principal questions under debate is if the Early Holocene peopling of southern Arabia was mainly due to input from the Levant during the Pre-Pottery Neolithic B, to the expansion of an autochthonous population, or some combination of these demographic processes. Since previous genetic studies have not been able to include all parts of southern Arabia, we have helped fill this lacuna by collecting new population datasets from Oman (Dhofar) and Yemen (Al-Mahra and Bab el-Mandab). We identified several new haplotypes belonging to haplogroup R2 and generated its whole genome mtDNA tree with age estimates undertaken by different methods. R2, together with other considerably frequent southern Arabian mtDNA haplogroups (R0a, HV1, summing up more than 20% of the South Arabian gene pool) were used to infer the past effective population size through Bayesian skyline plots. These data indicate that the southern Arabian population underwent a large expansion already some 12 ka. A founder analysis of these haplogroups shows that this expansion is largely attributed to demographic input from the Near East. These results support thus the spread of a population coming from the north, but at a significantly earlier date than presently considered by archaeologists. Our data suggest that some of the mtDNA lineages found in southern Arabia have persisted in the region since the end of the Last Ice Age.