Alpha-thalassemia in northern Thailand. Frequency of deletional types characterized at the DNA level

The frequency of alpha-thalassemias in northern Thailand was estimated using DNA techniques. Among 106 healthy adult Thais from the Chiangmai area, 28 were shown to carry alpha-globin gene anomalies. There were 19 heterozygotes and 1 homozygote for alpha-thalassemia-2. One of the alpha-thalassemia-2 deletions was of the -alpha 4.2 type and the remaining 20 of the -alpha 3.7 type (subtype I). Deletions of both alpha-globin genes on one chromosome (alpha-thalassemia-1) of the Southeast Asian type were observed in 5 cases, and 3 alpha-globin gene triplications were identified. Compared with a previous report on alpha-thalassemia in northern Thailand which was based on the determination of hemoglobin Bart's in cord blood, the present DNA study reveals a similar frequency of alpha-thalassemia-2 but a considerably lower frequency of alpha-thalassemia-1.     

The distribution of the Hb Constant Spring gene in Southeast Asian populations

Summary The distribution of the hemoglobin Constant Spring (Hb CS) gene in eight populations in Southeast Asia (including Assam) was determined using oligonucleotide hybridization. Hb CS was absent in two Assamese populations with a high prevalence of Hb E. The Hb CS gene frequency was 0.033 in northern Thailand and near 0.01 in central Thailand and Cambodia. High frequencies, between 0.05 and 0.06, were observed in northeastern Thailand. The present data and a similar study in Laotians suggest that the Lao-speaking populations of the Mekong River basin in northeastern Thailand and Laos have the highest frequencies of the Hb CS gene in Southeast Asia.     

The spectrum of β-thalassemia mutations in northern and northeastern Thailand

Summary A total of 123 -thalassemia genes from northern (n = 113) and northeastern (n = 10) Thailand were examined. Using five oligonucleotide probes, the mutation in 108 genes (88%) was identified: 50 nonsense 17, 49 frameshift 41-42, 4-28(AG), 2IVS1 nt5(GC), 2IVS2 nt654, and 1 deletion removing the entire -globin gene. The nonsense 17 mutation (n = 39) was linked to a single haplotype, whereas the frameshift 41-42 mutation occurred with several haplotypes. The results of the present study indicate that prenatal diagnosis of clinically important -thalassemia syndromes using a limited set of oligonucleotides is feasible in approximately 80% of affected families in northern Thailand and most of the families with -thalassemia-Hb E disease in northeastern Thailand.     

β-Globin gene linked DNA haplotypes and frameworks in three South-East Asian populations

Summary DNA haplotypes and frameworks (numbers in parenthesis) linked to the -globin gene were determined by restriction fragment analysis using eight restriction endonucleases on 86 (97) chromosomes bearing the normal -globin gene (HBB^*A) and 108 (118) chromosomes bearing HBB^*E in subjects homozygous for HBB^*A or HBB^*E from three South-East Asian populations with high HBB^*E frequencies (northern Thailand, north-eastern Thailand and Cambodia). A systematic nomenclature for -globin gene-linked haplotype characterized by six polymorphic sites is introduced. In all populations, HBB^*A occurred preferentially (>80%) in linkage with the haplotype 41 (+----+) and all three frameworks described by Antonarakis et al. (1982). In contrast, almost 80% of the HBB^*E genes occurred with the haplotype 27 (-+-+++). In northern and north-eastern Thailand, HBB^*E was present almost exclusively in framework 2; HBB^*E in framework 3 (Asian) was limited to the Khmer population of Cambodia, and the frequency of HBB^* E-linked framework 3 increased from the west to the east in this country.     

Microsatellite profiles reveal an unexpected genetic relationship between Asian populations

Allelic frequencies for up to five short tandem repeat systems (HumTH01, HumVWA, HumF13B, HumCD4, HumD21S11) were analyzed in seven population samples from Asia using the polymerase chain reaction and gel electrophoresis. No deviations from Hardy-Weinberg equilibrium were observed. Two new alleles of the CD4 and TH01 loci were detected, and sequenced and their molecular structure is presented. A phylogenetic tree based on Thai, Han Chinese (from the northeast of China), Japanese, German and Ovambo allelic frequencies was constructed and demonstrates the close relationship of the Asian populations. Additionally, allelic frequency data for the VWA and TH01 systems were determined for the south Chinese minorities Bai, Dai and Qiang and for Koreans and compared with the above data. The Bai and Dai populations were clear outliers of the cluster of all other Asians, indicating an unexpected pattern of genetic heterogeneity of the Chinese nation. Two clusters of Asian populations could be established: the Koreans and Japanese together with the Han and Qiang Chinese, and, forming a separate cluster, the Bai and Dai populations. Received: 10 June 1997 / Accepted: 15 March 1998     

Study of alpha-thalassemia in northeastern Thailand at the DNA level

The frequency of alpha-thalassemias in a general population sample from northeastern Thailand and in an Austroasiatic group with high frequencies of hemoglobin E and beta-thalassemia, the So, was estimated using DNA techniques. Among 64 healthy adult subjects from the Khonkaen and Ubol areas, the following haplotype frequencies were determined: alpha alpha, 0.742; -alpha 3.7 (subtype I), 0.148; -alpha 4.2, 0.016; -alpha del, 0.008; alpha Constant Spring alpha, 0.055; --SEA, 0.023, and alpha alpha alpha (triplicated alpha-globin gene), 0.008. In the So group, the combined frequency of alpha-thalassemia chromosomes was 0.525.     

Prevalence of α-thalassemias in northern Thailand

The population of northern Thailand has one of the highest frequencies of α-thalassemia in the world. However, the available distributional data are controversial. In addition to deletional types of α-thalassemia Hb, type Constant Spring should also be taken into consideration in α-thalassemia population studies, because it causes clinical α-thalassemia in the homozygous state or when present with both α-globin genes deleted in trans. We have examined a sample of 215 healthy subjects from four rural districts of Chiang Mai province. Out of these, 77 exhibited anomalies of the α-globin genes (αα/-α^3.7 in 36; -α^3.7/-α^3.7 in 3; ––^SEA in 30; αα/α^CSα in 5; ααα^anti3.7 in 3). Therefore, no fewer than 2% of the children in northern Thailand are expected to be born with HbH disease or thalassemic hydrops fetalis. The considerable public health problem of hemoglobinopaties and the increasing acceptance of family planning necessitates facilities for the pre- and postnatal diagnosis of these disorders at the DNA level. Received: 4 March 1996 / Revised: 9 April 1996     

Cytochrome b-560, a new component of thylakoid membranes

During a survey of a series of electron transport mutants of Chlamydomonas reinhardtii, we have observed a hitherto unrecognised component, cytochrome b-560, in a strain (F18) which entirely lacks the cytochrome bf complex. This component is present at approx. 1 nmol/mg chlorophyll, has a midpoint potential of −125 mV (n = 1) at pH 7.2 and is slowly reduced by dithionite. The cytochrome was also observed in thylakoid membranes prepared from wild-type Chlamydomonas and from higher plants after extraction of the cytochrome bf complex by detergent treatment. It could not be observed in thylakoid membrane fragments prepared from the cyanobacterium Phormidium laminosum.