Prenatal diagnosis of α- and β-thalassemias in southern Thailand

We report our work on prenatal diagnosis of α-thalassemia, β-thalassemia and other hemoglobinopathies in southern Thailand. DNA-based diagnosis was offered to 1906 pregnancies at risk for thalassemia using a combination method of multiplex-PCR and reverse dot blot analysis to detect seven α-globin and 47 β-globin mutations. The most commonly detected mutation of α⁰-thalassemia was a South-East Asian deletion (98%), followed by a Thai deletion (2%). Twenty-eight β-globin mutations were identified. Fourteen common mutations, including cod 19 A-G (18.6%), cod 41/42 -TCTT (14.4%), IVS1#5 G-C (13.2%), 3.5 kb deletion (9.2%), cod 17 A-T (7.7%), -28 A-G (7.3%), IVSI#1 G-T (7.1%), 12.5 kb deletion (δβ)⁰ (5.7%), HPFH6 (4.2%), IVS2#654 C-T (2.7%), 45 kb deletion (1.9%), Asian Indian-inversion-deletion Gγ(Aγδβ)⁰ (1.6%), cod 41 -C (1.5%) and cod 71/72 +A (1.3%) were detected, accounting for 96.5% of all mutations detected. The most common hemoglobin variant was Hb E, accounting for 97.86%. Prenatal diagnosis of 1906 couples at risk showed 22.0% normal, 51.2% carrier and 26.8% affected. The present study provides important information for diagnosis and control of severe thalassemia diseases.

MiR-155 enhances phagocytic activity of β-thalassemia/HbE monocytes via targeting of BACH1

Abnormal red blood cell (RBC) clearance in β-thalassemia is triggered by activated monocytes. Recent reports indicate that miRNA (miR-) plays a role in monocyte activation. To study phagocytic function, we co-cultured monocytes of normal, non-splenectomized and splenectomized β-thalassemia/HbE individuals with RBCs obtained from normal, non-splenectomized and splenectomized β-thalassemia/HbE individuals. The phagocytic activity of β-thalassemia/HbE monocytes co-cultured with β-thalassemia/HbE RBCs was significantly higher than that of normal monocytes co-cultured with normal RBCs. Upregulation of monocyte miR-155 was observed in β-thalassemia/HbE patients. Increased miR-155 was associated with reductions in BTB and CNC Homology1 (BACH1) target gene expression and increased phagocytic activity of β-thalassemia/HbE monocytes. Taken together, these findings suggested that increased miR-155 expression in activated monocytes leads to enhanced phagocytic activity via BACH-1 regulation in β-thalassemia/HbE. This provides novel insights into the phagocytic clearance of abnormal RBCs in β-thalassemia/HbE.

A novel 105 basepair deletion causing beta(0)-thalassemia in members of a Thai family

We identified and characterized a novel beta(0)-thalassemia mutation due to partial deletion of the 5' end beta-globin gene including the mRNA cap site and a part of exon 1. The deletion was precisely 105 basepair (bp) in length extending from position -24 or -25 to +80 or +81 relative to the beta-globin gene mRNA cap site. This mutation was detected in three individuals from a family originating in the area of southern Thailand. The propositus was a 39-year-old female and noted to be heterozygous for beta-thalassemia with hemoglobin (Hb) level of 10.1 g/dl, MCV 70 fl, MCH 23.1 pg, HbA2 6.3%, and HbF 2.4%. Her son was 9 years of age and was also heterozygous for the mutation, having Hb level of 10.8 g/dl, MCV 58 fl, MCH 19.0 pg, HbA2 5.6%, and HbF 4.3%. Her 6-year-old daughter was affected, having a genotype of this mutation and a G-C transition at IVS 1 nt 5. Although the deletion does not include the beta-globin gene promoter sequences, the individuals heterozygous for this mutation have an elevated HbA2 level slightly higher than observed in most carriers of beta-thalassemia caused by point mutations.

Prenatal diagnosis of beta-thalassaemia by reverse dot-blot hybridization

Thalassaemia is the most common genetic disease and is a public health problem of Thailand. Prevention and control of beta-thalassaemia diseases need accurate diagnosis of carriers and proper genetic counselling. Prenatal diagnosis is needed to prevent birth of the thalassaemic offspring in the couple at risk. This can be performed in the first trimester of pregnancy by DNA analysis using the polymerase chain reaction (PCR). Since there are more than 20 mutations causing beta-thalassaemia in Thailand, the point mutation detection by reverse dot-blot allele-specific oligonucleotide (ASO) hybridization was developed using two sets of ASO probes. The first battery of ASO probes has been designed to detect 10 common beta-globin gene mutations including codon 26, G->A (Hb E): codons 41/42, -TCTT; codon 17, A->T; IVS 2 nt 654, C->T; IVS 1 nt 1, G->T; IVS 1 nt 5. G->C; codon 19, A->G (Hb Malay); codon 35, C->A; codons 71/72, +A and -28 ATA, A->G. The second set of ASO probes detect 14 uncommon beta-thalassaemia mutations. We applied this reverse dot-blot hybridization technique to perform prenatal diagnosis in 105 pregnancies at risk of having severe beta-thalassaemia diseases. 36 fetuses (34 per cent) were found to be affected with homozygous beta-thalassaemia or beta-thalassaemia/Hb E disease in which one was twin pregnancy. The others included 31 fetuses with heterozygous beta-thalassaemia, 22 heterozygous Hb E, 1 homozygous Hb E and 16 normal fetuses. The common set of ASO probes detected about 95 per cent of cases which suggests that prenatal diagnosis for beta-thalassaemia disease can be easily carried out by this approach.

Analysis of beta-thalassemia mutations and beta-locus control region hypersensitive sites 2, 3 and 4 in southern Thailand

beta-Thalassemia mutations in 221 chromosomes of unrelated southern Thai patients were analyzed. Using dot blot hybridization of PCR amplified DNA with 15 allele specific oligonucleotide probes for beta-thalassemia mutations 196/221 (89%) of the alleles were characterized. Ten mutations were identified, of which six [codon 41/42 (TTCTTT-TT), IVS1 nt5(G-C), codon 19 (AAC-AGC), codon 17 (AAG-TAG), IVS1 nt1(G-T), -28 TATA (A-G)], accounted for 85%. Among the 25 uncharacterized alleles, 15 were analyzed by automated fluorescent DNA sequencing of the whole beta-globin gene with normal results in 7 alleles. Four mutations, previously described were detected in 8 alleles. They were a G-A at IVS1 nt1 in one heterozygote, a G-T at IVS1 nt1 in one heterozygote, codon 15 (TGG-TAG) in two heterozygotes and poly A(AATAAA-AATAGA) in two homozygotes. The polyadenylation mutations, previously demonstrated in the Malaysian population have been first detected in Thailand. It is remarkable that the IVS1 nt1 (G-A) mutation, previously reported in the Mediterranean population has been found only in the south of Thailand. This mutation was probably imported from Portugal. In former times the Portuguese had settled in Phuket in southern Thailand. In order to find a causative mutation in the rest of 7 true unknowns we performed direct DNA sequencing of the core fragments of the beta-Locus Control Region Hypersensitive Sites (LCR HS) 2,3 and 4 in these 7 samples. DNA sequencing of HS2 and HS3 fragments showed normal results. The heterozygote A/G was present in the palindromic sequence of the LCR HS4 (TGGGGACCCCA) in 6 beta-thalassemia samples. The same heterozygote A/G was found in 5/12 normal subjects. The allele frequency of A (0.79) is obviously higher than that of G (0.21). This could be due to the stability of the palindromic structure. When an A is in the middle of the palindromic sequence, the hairpin structure is formed. In contrast the hairpin structure disappears when a G is in the middle of the palindromic sequence. This structure is not further symmetric and may not be so stable as the hairpin structure. beta-Thalassemia mutations in southern Thailand are very heterogeneous and their distribution is different from other parts of the country.

Molecular basis of beta-thalassemia in Thai Muslim patients in the the south of Thailand

Among a sample of 29 unrelated Thai Muslim children, a total of 37 beta thalassemia genes was identified and 33 out of 37 mutations (89%) were characterized giving 6 different mutations. Four mutations [IVS-1 nt 5 (G-C), codon 19 (A-G), codons 41/42 (-CTTT) and IVS-1 nt 1 (G-T)] account for 86%. IVS-1 nt 5 (G-C) is the most common mutation found in Thai Muslim patients. Thai Muslim patients share the four most common mutations with Malays.

Clinical, hematological and molecular features in Thais with beta-Malay/beta-thalassemia and beta-Malay/HbE

A total of 50 patients and relatives were studied comprising 12 cases of compound heterozygosity of beta-Malay and beta + thalassemia, 10 cases of compound heterozygosity of beta-Malay and beta degree thalassemia, 10 cases of beta-Malay and HbE and 18 cases of beta-Malay heterozygosity. Patients with beta-Malay and HbE had very mild clinical symptoms or were asymptomatic of thalassemia disease in the absence of blood transfusion. Homozygosity of beta-Malay produce mild clinical symptoms of thalassemic disease with normal facial characteristics and were not transfusion dependent. Patients with beta-Malay and IVS 1 nt 5 (G-C) had severe clinical symptoms, and were transfusion dependent. Patients with beta-Malay and beta degree thalassemia had severe clinical symptoms, delayed weight and height in relation to age, were transfusion dependent and had classical features of thalassemic diseases.

Comparative studies of the CAG repeats in the spinocerebellar ataxia type 1 (SCA1) gene

The CAG repeat tract at the autosomal dominant spinocerebellar ataxia type 1 (SCA1) locus was analyzed in SCA1 families and French-Acadian, African-American, Caucasian, Greenland Inuit, and Thai populations. The normal alleles had 9-37 repeats, whereas disease alleles contained 44-64 repeats. The CAG repeat tract contained one or two CAT interruptions in 44 of 47 normal human chromosomes and in all five chimpanzees examined. In contrast, no CAT interruptions were found in Old World monkeys or expanded human alleles. The number and positions of CAT interruptions may be important in stabilizing CAG repeat tracts in normal chromosomes. At least five codons occupy the region corresponding to the polyglutamine tract at the SCA1 locus in mice, rats, and other rodents. They comprise three or four CCN (coding for proline) in addition to one or two CAG repeats.

Analysis of CAG repeat of the Machado-Joseph gene in human, chimpanzee and monkey populations: a variant nucleotide is associated with the number of CAG repeats

Machado-Joseph disease (MJD) is an autosomal dominant neurodegenerative disorder associated with an unstable and expanded CAG repeat. We analyzed this locus from various sources including MJD families, Acadian, African American, Caucasian, Greenland Inuit and Thai populations. The range of the CAG repeat size was 14-40 in the normal alleles while the MJD alleles contained 73-78 repeats in our studies. We found 25 different alleles on normal chromosomes with a heterozygosity of 0.86 in combined populations. The most common alleles were 23 (22.9%) and 14 (25.5%) repeats. We also examined 16 chimpanzees and various Old World monkeys: a pigtail macaque, a mangabey and 12 rhesus macaques. The DNA sequences surrounding the CAG repeat did not vary among species. The range of the number of the CAG repeats is 13-14 in macaques, 16 in mangabey and 14-20 in chimpanzees. Variant CAA or AAG triplets in the CAG repeat tracts were found in all 268 human, 28 monkey and 32 chimpanzee chromosomes. As reported in a previous study [Kawaguchi et al. (1994) Nature Genet. 8, 221-228] the common variant positions were the third (CAA), fourth (AAG) and sixth (CAA) positions. However, we found three human chromosomes containing CAG at the sixth position and the mangabey had AAG at the ninth position. In addition, we found CAG at the fourth position and AAG at the sixth position in all macaque chromosomes. The nucleotide following the CAG repeat tract was usually G in all species studied. However, we sometimes found C at this position in human and chimpanzee chromosomes. Interestingly, this variant C was found in all expanded chromosomes and in 54.5% of chromosomes with 27-40 CAG repeats but it was not found in any chromosomes with less than 20 CAG repeats. We hypothesize that the variant C may be associated with CAG repeat instability.

Towards a suitable antigen for diagnosis of Gnathostoma spinigerum infection

Advanced third-stage larvae of G. spinigerum were obtained from two separate sources, namely from cysts in the livers of naturally infected eels (L3E) and from experimentally infected mice (L3M). Morphology of the L3E was studied microscopically. The larvae were homogenized in distilled water, 1% Triton X-100 or 1% sodium deoxycholate containing protease inhibitors. Protein compositions of the three crude extracts were compared, on the same weight basis, by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and Coomassie brilliant blue staining while their antigenicities were studied by Western blot analysis using serum of a patient with parasitologically confirmed gnathostomiasis. Distilled water was found to be the best extraction solution in solubilizing proteins especially the diagnostic antigen, namely the 24,000 (24 kDa) mol. wt component from the larvae. The L3E and L3M contained relatively equal amounts of the 24 kDa antigen. This diagnostic component was anatomically located in the body fluid, oesophagus and intestine of the larva.

Molecular basis of beta thalassemia in the south of Thailand

A total of 103 beta thalassemia genes from 78 children (45 with Hb E/beta thalassemia, 8 with beta thalassemia heterozygotes, and 25 with homozygous beta thalassemia) were analyzed using dot-blot hybridization of the polymerase chain reaction-amplified DNA and direct DNA sequencing. Nine mutations were characterized in 98/103 (95%) of beta thalassemia alleles, of which six (a 4 bp deletion in codons 41-42, a G-C transition at position 5 of IVS-1, A-G transition at codon 19, an A-T transition at codon 17, an A-G transition at position -28 upstream of the beta globin gene, a G-T transition at position 1 of IVS-1), accounted for 92%. The spectrum of beta thalassemia mutations in Chinese Thai is similar to that reported among the Chinese from other parts of the world. The distribution of beta thalassemia mutations in Muslim Thai is similar to that reported among Malaysians. The most common beta thalassemia mutation in Thai and Chinese Thai patients is the frameshift mutation at codons 41-42, in comparison with the Muslim Thai in whom the G-C transition at position 5 of the IVS-1 mutation predominates. The heterogeneity of molecular defects causing beta thalassemia should aid in the planning of a prenatal diagnosis program for beta thalassemia in the South of Thailand.

Molecular heterogeneity of beta-thalassemia in Thailand

beta-Globin genes in 294 chromosomes of beta-thalassemia homozygotes and patients of beta-thalassemia/HbE in the northeast, the middle and the south of Thailand were analyzed by the PCR related techniques: dot blot hybridization, direct restriction assay, direct cloning and direct sequencing of the amplified DNA fragments. Twelve different mutations were detected at various frequencies. They are an A-G at-28, codon 19 (AAC-AGC), a G-T at IVS-1 nt1,a G-C at IVS-1 nt5, a C-T at IVS-2 nt654, a G addition in codons 8/9, a C deletion in codon 41, a 4 bp deletion in codons 41/42, an A addition in codons 71/72, an AAG-TAG in codon 17, a CAG-TAG in codon 26, a TAC-TAA in codon 35 and a 8 bp deletion in codons 123-125. We also developed allele specific-polymerase chain reaction to facilitate non-radioactive detection of the mutation. Origins and spread of mutations are speculated based on the results of determination of haplotypes and frameworks that are linked to the thalassemia alleles.

Monoclonal antibody to a diagnostic Mr 24,000 antigen of Gnathostoma spinigerum

Crude water extract (CA) was prepared from the advanced third-stage larvae of Gnathostoma spinigerum collected from livers of naturally infected eels. The extract was partially purified by chromatofocussing column chromatography and the fraction which contained specific antigen of G. spinigerum which was an Mr 24,000 glycoprotein was used to immunize five Balb/c mice for preparing immune splenocytes. Spleen cells were collected from one mouse which showed high serum titre by indirect enzyme-linked immunosorbent assay and contained specific antibody to the Mr 24,000 antigen as checked by Western blot analysis. The spleen cells were fused with myeloma Sp2/0 cells at a ratio of 10 spleen cells per one myeloma cell using polyethylene glycol 3350 as a fusogen. Thirteen out of 174 growing polyclones (7.5%) produced antibodies to the partially purified CA fraction. Among them, two polyclones produced antibody directed to the Mr 24,000 protein. These two polyclones were subjected to monocloning by limiting dilution and a monoclone GN6/24 which produced monoclonal antibody to the specific Mr 24,000 protein of G. spinigerum was obtained.

Purification of Gnathostoma spinigerum specific antigen and immunodiagnosis of human gnathostomiasis

Specific antigen of G. spinigerum which has been shown to be a protein with a relative mol. wt of 24,000 (24K) was prepared from the advanced third-stage larvae (L3) obtained from the livers of naturally infected eels. The L3 were ground and extracted with water. Purification procedures involved gel filtration, chromatofocussing and anion exchange column chromatographies, while characterization of the specific antigen was performed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and staining, Western blot analysis and isoelectric focussing. The specific antigen which has a pI of 8.5 was used as antigen in the indirect enzyme-linked immunosorbent assay (ELISA) to detect specific antibody in four groups of individuals, namely five parasitologically diagnosed gnathostomiasis patients (group 1); 15 clinically diagnosed gnathostomiasis patients (group 2); 136 patients with other parasitic infections (group 3); and 25 normal healthy parasite-free controls. Sensitivity, specificity and predictive values (positive and negative) of the assay were 100%.

Specific antigen of Gnathostoma spinigerum for immunodiagnosis of human gnathostomiasis

Sera from four patients with parasitologically confirmed gnathostomiasis, 15 patients with presumptive gnathostomiasis, 64 patients with various parasitic infections and 19 healthy adults were studied by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis for their reactivities against somatic extract of Gnathostoma spinigerum third-stage larvae (L3). It was found that the L3 extract was highly complex consisting of more than 20 antigenic components, a few of which gave reactions with sera from the healthy controls. Extensive cross-reactions of the parasite's antigen with sera from patients with other parasitic infections occurred. A specific antigen of G. spinigerum with a mol. wt of 24,000 (24k) was found to react with all parasitologically proven patients, five of the presumptive patients, one of the patients with other parasitic infections and none of the healthy individuals. This 24k component of G. spinigerum is a potential diagnostic antigen for use in the immunodiagnosis of human gnathostomiasis.

Antibody responses in human gnathostomiasis

Sera from 4 patients with parasitologically confirmed gnathostomiasis and from 18 healthy individuals were studied by SDS-PAGE and Western blot analysis using radioiodinated protein A to detect antibody responses against crude aqueous somatic extract of advanced third stage larvae of Gnathostoma spinigerum (L3G). It was found that the L3G extract was highly complex, comprising of more than 40 polypeptides among which more than 20 components were antigenic in human. The relative M.W. of the proteins ranged from 13 kd to 150 kd with the major antigenic bands at 150, 135, 120, 94, 84, 82, 72, 55, 54, 49, 43, 38, 35, 32 and 28 kd. All 4 sera from gnathostomiasis patients gave almost an identical pattern of reactivities against the L3G antigens whereas sera from the normal individuals gave much lower reactivities against the L3G antigen of M.W. 38 kd and, in certain individuals, those of 49 and 43 kd. The present findings suggest that the serum antibody response against the parasite is specific and may be useful in a specific or a confirmed immunodiagnosis of human gnathostomiasis.