Insight into the Peopling of Mainland Southeast Asia from Thai Population Genetic Structure

There is considerable ethno-linguistic and genetic variation among human populations in Asia, although tracing the origins of this diversity is complicated by migration events. Thailand is at the center of Mainland Southeast Asia (MSEA), a region within Asia that has not been extensively studied. Genetic substructure may exist in the Thai population, since waves of migration from southern China throughout its recent history may have contributed to substantial gene flow. Autosomal SNP data were collated for 438,503 markers from 992 Thai individuals. Using the available self-reported regional origin, four Thai subpopulations genetically distinct from each other and from other Asian populations were resolved by Neighbor-Joining analysis using a 41,569 marker subset. Using an independent Principal Components-based unsupervised clustering approach, four major MSEA subpopulations were resolved in which regional bias was apparent. A major ancestry component was common to these MSEA subpopulations and distinguishes them from other Asian subpopulations. On the other hand, these MSEA subpopulations were admixed with other ancestries, in particular one shared with Chinese. Subpopulation clustering using only Thai individuals and the complete marker set resolved four subpopulations, which are distributed differently across Thailand. A Sino-Thai subpopulation was concentrated in the Central region of Thailand, although this constituted a minority in an otherwise diverse region. Among the most highly differentiated markers which distinguish the Thai subpopulations, several map to regions known to affect phenotypic traits such as skin pigmentation and susceptibility to common diseases. The subpopulation patterns elucidated have important implications for evolutionary and medical genetics. The subpopulation structure within Thailand may reflect the contributions of different migrants throughout the history of MSEA. The information will also be important for genetic association studies to account for population-structure confounding effects.     

Heterostemma trilobatum sp. nov. (Apocynaceae: Asclepiadoideae) from Thailand

A new species, Heterostemma trilobatum A. Kidyoo & Thaithong has been discovered in northern, northeastern and southeastern Thailand. It is here described, illustrated and meticulously compared with a morphologically similar species, H. xuansonense T. B. Tran & J. Hw. Kim. Both species resemble each other, having sessile to subsessile cymes, five glands on the inside of the calyx and dark red to purplish red ovate corona lobes. However, H.trilobatum is markedly differentiated by much smaller size of flowers and the presence of peculiar trilobed corona appendages.     

A genome-wide association identified the common genetic variants influence disease severity in β0-thalassemia/hemoglobin E

β-Thalassemia/HbE disease is clinically variable. In searching for genetic factors modifying the disease severity, patients were selected based on their disease severities, and a genome-wide association study (GWAS) was performed. Genotyping was conducted with the Illumina Human 610-Quad BeadChips array using DNAs from 618 Thai β⁰-thalassemia/HbE patients who were classified as 383 severe and 235 mild phenotypes by a validated scoring system. Twenty-three SNPs in three independent genes/regions were identified as being significantly associated with the disease severity. The highest association was observed with SNPs in the β-globin gene cluster (chr.11p15), and rs2071348 of the HBBP1 gene revealed the most significant association [P = 2.96 × 10^?13, odds ratio (OR) = 4.33 (95% confidence interval (CI), 2.74–6.84)]. The second was identified in the intergenic region between the HBS1L and MYB genes (chr.6q23), among which rs9376092 was the most significant [P = 2.36 × 10^?10, OR = 3.07 (95% CI, 2.16–4.38)]. The third region was located in the BCL11A gene (chr.2p16.1), and rs766432 showed the most significant association [P = 5.87 × 10^?10, OR = 3.06 (95% CI, 2.15–4.37)]. All three loci were replicated in an independent cohort of 174 Indonesian patients. The associations to fetal hemoglobin levels were also observed with SNPs on these three regions. Our data indicate that several genetic loci act in concert to influence HbF levels of β⁰-thalassemia/HbE patients. This study revealed that all the three reported loci and the α-globin gene locus are the best and common predictors of the disease severity in β-thalassemia.     

Dischidia kerrii sp. nov. (Apocynaceae: Asclepiadoideae) from northeastern Thailand

Dischidia kerrii is presented as a new species from northeastern Thailand. This newly discovered species is thoroughly described, discussed and illustrated. A comparison is made with the putative closely related species D. acuminata. They can be distinguished by differences in corolla lobes and staminal corona lobes.     

Gymnemopsis phuwuaensis (Apocynaceae,Asclepiadoideae), a new species from northeastern Thailand

A new species, Gymnemopsis phuwuaensis A. Kidyoo, has been discovered in northeastern Thailand and is here described and illustrated. An identification key to all species of the genus is provided. Photographs and a diagnostic comparison with the morphologically similar species G. calcicola Kerr, are also provided. Gymnemopsis phuwuaensis displays clear differences in form and color of the corolla as well as in size of bract and flower. A lectotype for Gymnemopsis pierrei is also designated.