Hemoglobin E Prevalence among Ethnic Groups Residing in Malaria-Endemic Areas of Northern Thailand and Its Lack of Association with Plasmodium falciparum Invasion In Vitro

Novel secretory organelles of parasite origin - at the center of host-parasite interaction

Reorganization of cell organelle-deprived host red blood cells by the apicomplexan malaria parasite Plasmodium falciparum enables their cytoadherence to endothelial cells that line the microvasculature. This increases the time red blood cells infected with mature developmental stages remain within selected organs such as the brain to avoid the spleen passage, which can lead to severe complications and cumulate in patient death. The Maurer's clefts are a novel secretory organelle of parasite origin established by the parasite in the cytoplasm of the host red blood cell in order to facilitate the establishment of cytoadherence by conducting the trafficking of immunovariant adhesins to the host cell surface. Another important function of the organelle is the sorting of other proteins the parasite traffics into its host cell. Although the organelle is of high importance for the pathology of malaria, additional putative functions, structure, and genesis remain shrouded in mystery more than a century after its discovery. In this review, we highlight our current knowledge about the Maurer's clefts and other novel secretory organelles established within the host cell cytoplasm by human-pathogenic malaria parasites and other parasites that reside within human red blood cells.

Indian genetic heritage in Southeast Asian populations

The great ethnolinguistic diversity found today in mainland Southeast Asia (MSEA) reflects multiple migration waves of people in the past. Maritime trading between MSEA and India was established at the latest 300 BCE, and the formation of early states in Southeast Asia during the first millennium CE was strongly influenced by Indian culture, a cultural influence that is still prominent today. Several ancient Indian-influenced states were located in present-day Thailand, and various populations in the country are likely to be descendants of people from those states. To systematically explore Indian genetic heritage in MSEA populations, we generated genome-wide SNP data (using the Affymetrix Human Origins array) for 119 present-day individuals belonging to 10 ethnic groups from Thailand and co-analyzed them with published data using PCA, ADMIXTURE, and methods relying on f-statistics and on autosomal haplotypes. We found low levels of South Asian admixture in various MSEA populations for whom there is evidence of historical connections with the ancient Indian-influenced states but failed to find this genetic component in present-day hunter-gatherer groups and relatively isolated groups from the highlands of Northern Thailand. The results suggest that migration of Indian populations to MSEA may have been responsible for the spread of Indian culture in the region. Our results also support close genetic affinity between Kra-Dai-speaking (also known as Tai-Kadai) and Austronesian-speaking populations, which fits a linguistic hypothesis suggesting cladality of the two language families.

Micromapping of Thalassemia and Hemoglobinopathies Among Laos, Khmer, Suay and Yer Ethnic Groups Residing in Lower Northeastern Thailand

Northeastern (NE) Thailand is one of the areas with a prevalence of thalassemias and hemoglobinopathies. Data on the prevalence of the diseases in minorities in the region has been limited. This study aimed to survey the thalassemias and hemoglobinopathies that take into account ethnicity. Four ethnic groups, including Laos (n = 162), Khmer (n = 145), Suay (n = 134), and Yer (n = 101) inhabiting the lower region of NE Thailand, were selected to represent the study populations. The results demonstrated that an extremely high prevalence of Hb E (HBB: c.79G>A) (>50.0%) was observed in the Khmer, Suay and Yer ethnic groups. The highest prevalence of α⁺-thalassemia (α⁺-thal) [-α^3.7 (rightward)] deletion was found in the Khmer ethnic group (48.28%). The -α^4.2 (leftward) deletion (α⁺-thal) was restricted to the Yer ethnic group. Yer and Suay had a high incidence of Hb Constant Spring (Hb CS; HBA2: c.427T>C) as well as Hb Paksé (HBA2: c.429A>T). As the prevalence of α⁰-thalassemia (α⁰-thal) is relatively high in Suay (7.46%), couples who are members of Suay ethnic population should be urged to undergo hematological screening before planning a pregnancy to control the Hb Bart's hydrops fetalis. Micromapping of thalassemias and hemoglobinopathies herein described will be helpful in genetic counseling and public education campaigns, which should be carried out in appropriate languages, with exhibitions at the village levels. This information will be of benefit for the long-term effort to reduce the burden of severe thalassemia disease in the region.

Paternal genetic history of the Yong population in northern Thailand revealed by Y-chromosomal haplotypes and haplogroups

We have determined the distribution of Y-chromosomal haplotypes and haplogroups in the Yong population, one of the largest and well-known ethnic groups that began migrating southward from China to Thailand centuries ago. Their unique mass migration pattern provided great opportunities for researchers to study the genetic links of the transboundary migration movements among the peoples of China, Myanmar and Thailand. We analysed relevant male-specific markers, such as Y-STRs and Y-SNPs, and the distribution of 23 Y-STRs of 111 Yong individuals and 116 nearby ethnic groups including the Shan, Northern Thai, Lawa, Lua, Skaw, Pwo and Padong groups. We found that the general haplogroup distribution values were similar among different populations; however, the haplogroups O1b-M268 and O2-M112 constituted the vast majority of these values. In contrast with previous maternal lineage studies, the paternal lineage of the Yong did not relate to the Xishuangbanna Dai people, who represent their historically documented ancestors. However, they did display a close genetic affinity to other prehistoric Tai-Kadai speaking groups in China such as the Zhuang and Bouyei. Low degrees of genetic admixture within the populations who belonged to the Austroasiatic and Sino-Tibetan linguistic families were observed in the gene pool of the Yong populations. Resettlement in northern Thailand in the early part of the nineteenth century AD, by way of mass migration trend, was able to preserve the Yong's ancestral genetic background in terms of the way they had previously lived in China and Myanmar. Our study has revealed similar genetic structures among ethnic populations in northern Thailand and southern China, and has identified and emphasized an ancient Tai-Kadai patrilineal ancestry line in the Yong ethnic group.

Hemoglobin E, malaria and natural selection

It is known that there has been positive natural selection for hemoglobin S and C in humans despite negative health effects, due to its role in malaria resistance. However, it is not well understood, if there has been natural selection for hemoglobin E (HbE), which is a common variant in Southeast Asia. Therefore, we reviewed previous studies and discussed the potential role of natural selection in the prevalence of HbE. Our review shows that in vitro studies, evolutionary genetics studies and epidemiologic studies largely support an involvement of natural selection in the evolution of HbE and a protective role of HbE against malaria infection. However, the evidence is inconsistent, provided from different regions, and insufficient to perform an aggregated analysis such as a meta-analysis. In addition, few candidate gene, genome-wide association or epistasis studies, which have been made possible with the use of big data in the post-genomic era, have investigated HbE. The biological pathways linking HbE and malaria infection have not yet been fully elucidated. Therefore, further research is necessary before it can be concluded that there was positive natural selection for HbE due to protection against malaria.

Lay summary: Our review shows that evidence largely supports an involvement of natural selection in the evolution of HbE and a protective role of HbE against malaria. However, the evidence is not consistent. Further research is necessary before it is concluded.

Hemoglobin E protects against acute Plasmodium vivax infections in a Kachin population at the China-Myanmar border

OBJECTIVES

Hemoglobin E (HbE, β^{26 Glu-Lys}) is the most prevalent hemoglobinopathy in Southeast Asia. This study aimed to determine whether HbE protects against clinical Plasmodium vivax malaria in Southeast Asia.

METHODS

In a case-control study performed in villages along the China-Myanmar border, we determined the prevalence of HbE in 257 villagers who had acute P. vivax infections and in 157 control healthy villagers.

RESULTS

HbE in P. vivax patients (17.4%) was significantly less prevalent than in the healthy villager population (36.3%). Moreover, there was a complete lack of HbEE homozygotes in the vivax patients as compared to 9.5% prevalence in the healthy villagers. Using the HbAA group as the reference, both the HbEA heterozygotes and HbEE homozygotes had significantly lower odds of presenting with acute P. vivax infections. Furthermore, HbEA heterozygotes also had significantly lower P. vivax asexual parasite densities. HbEA did not affect the proportion of P. vivax patients with gametocytemia nor the gametocyte densities.

CONCLUSIONS

HbE offers significant protection against the occurrence and parasite density of acute P. vivax infections and provides a renewed perspective on P. vivax malaria as a potentially strong driving force behind the high frequencies of HbE in the Kachin population.

New insights from Thailand into the maternal genetic history of Mainland Southeast Asia

Tai-Kadai (TK) is one of the major language families in Mainland Southeast Asia (MSEA), with a concentration in the area of Thailand and Laos. Our previous study of 1234 mtDNA genome sequences supported a demic diffusion scenario in the spread of TK languages from southern China to Laos as well as northern and northeastern Thailand. Here we add an additional 560 mtDNA genomes from 22 groups, with a focus on the TK-speaking central Thai people and the Sino-Tibetan speaking Karen. We find extensive diversity, including 62 haplogroups not reported previously from this region. Demic diffusion is still a preferable scenario for central Thais, emphasizing the expansion of TK people through MSEA, although there is also some support for gene flow between central Thai and native Austroasiatic speaking Mon and Khmer. We also tested competing models concerning the genetic relationships of groups from the major MSEA languages, and found support for an ancestral relationship of TK and Austronesian-speaking groups.

Newborn Screening for Hemoglobinopathies and Red Cell Enzymopathies in Tripura State: A Malaria-Endemic State in Northeast India

Hemoglobinopathies are a group of inherited single gene disorders. There are reports on hemoglobin (Hb) variants identified in the tribal and non-tribal populations of Tripura State in northeastern India. This study aimed to determine the spectrum of hemoglobinopathies and enzymopathies by newborn screening in Tripura State and assess the extent of neonatal jaundice. A total of 2400 cord blood samples were collected and analyzed by high performance liquid chromatography (HPLC). Further confirmation of any abnormal HPLC was done by DNA analysis. The samples were also screened for deficiency of enzymopathies, glucose-6-phosphate dehydrogenase (G6PD) deficiency and pyruvate kinase. Of 2400 cord blood samples screened, 225 (9.3%) were Hb E (HBB: c.79G>A) heterozygotes, 80 (3.3%) were Hb E homozygotes and one carried Hb E-β-thalassemia (β-thal). Other Hb abnormalities were also detected including 15 Hb S (HBB: c.20A>T) heterozygotes, two Hb D-Punjab (HBB: c.364G>C) heterozygotes and two compound heterozygotes for Hb D-Punjab and Hb E. Of the 80 homozygous Hb E babies, four were non-tribal and 76 babies were tribal, and 225 patients carried Hb E trait, 141 were tribal, while 84 were non-tribal. Of 40 G6PD deficient babies identified, 13 had coinherited Hb E and two babies had pyruvate kinase deficiency. α Genotyping was performed in 162 affected babies, 50 of them carried α gene deletions. Newborn screening programs for Hb E, other hemoglobinopathies and G6PD deficiency must be encouraged in the malaria-endemic northeastern region of India. Drug-induced hemolysis can also be avoided by screening for G6PD deficiency at birth.

A comprehensive ethnic-based analysis of alpha thalassaemia allelle frequency in northern Thailand

Alpha (α)-thalassaemia is one of the most prevalent hereditary blood disorders, commonly affecting Southeast Asian people, with the highest incidence (30–40%) being seen in northern Thailand. However, this high incidence was estimated without consideration of the variations between ethnic populations and the geographical location of the populations. To address this issue, a total of 688 samples from 13 different northern Thai ethnic groups (30 villages) categorized into three linguistic groups were genotyped for deletional alpha-thalassaemia (-α^3.7, -α^4.2, --^SEA and --^THAI) and/or non-deletional alpha-thalassaemia (α^CS and α^PS) via multiplex gap-PCR and dot-blot hybridization, respectively. Alpha⁺(-α^3.7, -α^4.2, α^CS and α^PS) and alpha°-thalassaemia (--^SEA and --^THAI) allele frequencies (with 95% Confidence Interval) were the highest in the Sino-Tibetan group [0.13 (0.08–0.18)] and the Tai-Kadai group [0.03 (0.02–0.05)], respectively. With regards to ethnicity, the varying allele frequency of α⁺ and α°-thalassaemia amongst a variety of ethnic groups was observed. The highest α⁺-thalassaemia allele frequency was found in the Paluang [0.21 (0.10–0.37)] while α°-thalassaemia allele frequency was the highest in the Yuan [0.04 (0.01–0.10)]. These detailed results of alpha thalassaemia allele frequency and genetic diversity amongst the northern Thai ethnic groups demonstrate the need for ethnicity based thalassaemia prevention programs.

Endogamous marriage and the prevalence of hemoglobin E in ethnic groups of northern Thailand

OBJECTIVE

To investigate the impact of the endogamous marriage culture on the prevalence of the hemoglobin E (HbE) recessive variant.

METHODS

The prevalence of the hemoglobin E (HbE) recessive variant was determined by dot-blot hybridization in 4 endogamous villages (1 Mlabri and 3 Htin ethnic groups) in comparison with 9 other nearby non-endogamous populations.

RESULTS

Although the overall HbE prevalence in the population studied (8.44%, 33/391) was not significantly different from that of the general southeast Asian population, a high prevalence and individuals with homozygous HbE were observed in two villages, the Mlabri from Wiang Sa district and the Htin from Thung Chang district of Nan province (26.3% and 26.9%, respectively). The low HbE allelic frequency noticed in some endogamous populations suggests that not only endogamy but also other evolutionary forces, such as founder effect and HbE/β-thalassemia negative selection may have an effect on the distribution of the HbE trait.

CONCLUSION

Our study strongly documents that cultural impact has to be considered in the extensive prevalence studies for genetic disorders in the ethnic groups of northern Thailand.

Co-inheritance of glucose-6-phosphate dehydrogenase deficiency mutations and hemoglobin E in a Kachin population in a malaria-endemic region of Southeast Asia

Glucose-6-phosphate dehydrogenase (G6PD) deficiency and hemoglobin E (HbE, β26 Glu-Lys) are two common red cell disorders in Southeast Asia. G6PD deficiency produces hemolytic anemia, which can be triggered by certain drugs or infections. HbE is asymptomatic or is manifested as microcytic, minimally hemolytic anemia. The association between G6PD deficiency and HbE is little understood. This study aimed to investigate G6PD deficiency and HbE in a Kachin ethnic group in the China-Myanmar border area. G6PD enzyme activity was measured using a quantitative G6PD assay, G6PD variants genotyped by the SNaPshot assay, and an HbE gene mutation identified by an amplification refractory mutation system and subsequently confirmed by using a reverse dot blot hybridization assay from 100 unrelated individuals in the study area. G6PD enzyme activity ranged from 0.4 to 24.7 U/g Hb, and six males had severe G6PD deficiency (<0.12-1.2 U/g Hb), while six males and 12 females had mild G6PD deficiency (>1.2-4.5 U/g Hb). Among the 24 G6PD-deficient subjects, 22 (92%) had the Mahidol 487G>A mutation (12 male hemizygotes, one female homozygote, and nine female heterozygotes), while the G6PD genotypes in two female subjects were unknown. HbE was identified in 39 subjects (20 males and 19 females), including 15 HbEE (seven males and eight females) and 24 HbAE (13 males and 11 females). Twenty-three subjects co-inherited both G6PD deficiency and HbE (22 with HbAE and one with HbEE). Whereas mean Hb levels were not significantly different between the HbA and HbE groups, G6PD-deficient males had significantly lower Hb levels than G6PD-normal males (P < 0.05, t-test). However, it is noteworthy that two G6PD-deficient hemizygous males with HbAE were severely anemic with Hb levels below 50 g/L. This study revealed high prevalence of co-inheritance of G6PD deficiency with HbAE in the Kachin ethnicity, and a potential interaction of the G6PD Mahidol 487G>A and HbAE in males leading to severe anemia. The presence of 6% males with severe G6PD deficiency raised a major concern in the use of primaquine for radical cure of vivax malaria.

Autosomal STR variations reveal genetic heterogeneity in the Mon-Khmer speaking group of Northern Thailand

Since prehistoric times, Mon-Khmer speaking people have been recognized as indigenous ethnic groups living in northern Thailand. After the period of Tai colonization in the thirteenth century CE, the Mon-Khmer inhabitants were fragmented; some were expelled to rural areas while some were integrated into the mainstream of Tai society. Autosomal STR variations revealed that the present-day Mon-Khmer people could be genetically divided into two clusters. This finding appears to be consistent with the level of historical contact with the Tai majority ethnic groups. The cluster consisting of the Khamu, Lua, Paluang and Htin people, indicate that they have lived in remote areas and have had little historical contact with the Tai people. In this way, they appeared to have maintained aspects of their Mon-Khmer ancestral genetic bloodline but have genetically diverged from the Tai people. The cluster comprised of the Mon and Lawa people had an exclusively close relationship with the Tai people during the establishment of the prosperous Lan Na Kingdom. A fraction of the Tai genetic component investigated among the Mon people and some Lawa populations reflected the evidence of genetic admixture. However, some Lawa people, who have lived in the mountainous area of Mae Hong Son Province have exhibited a unique gene pool, which might have been shaped by the founder effect that occurred during their historical fragmentation. The rise of the genetic assimilation of the hill-tribe Karen people into the Mon-Khmer and the Tai gene pools indicated that different languages, cultures, and geographical distances have lost their power as barriers of inter-ethnic marriages in the present day.