The molecular basis of beta thalassaemia in Punjabi and Maharashtran Indians includes a multilocus aetiology involving triplicated alpha-globin loci

Hematological and genetic profiles of persons with co-inherited heterozygous β-thalassemia and supernumerary α-globin genes

INTRODUCTION

Thalassemias are common monogenic autosomal recessive hemoglobin disorders. The usually asymptomatic heterozygotes (β-thalassemia traits, βTT) may rarely develop non-transfusion-dependent-thalassemia (NTDT) due to co-inheritance of supernumerary α-globin genes. Literature on phenotypic/genotypic features of these rare combinations is limited.

MATERIALS AND METHODS

We studied the demographic, clinical, and laboratory data from 47 persons with co-inherited βTT + supernumerary α-globin genes. HBB mutations were tested for by ARMS-PCR and/or Sanger sequencing, ααα^(anti3.7) /ααα^(anti4.2) and deletional α-thalassemia testing by multiplex gap-PCRs, and Xmn1^G γ genotyping by PCR-RFLP.

RESULTS

The 47 cases comprised 0.08% of 61 010 hemoglobinopathy screenings during the study period. Mean age was 31.9 ± 14.7 years (range 5.5-83 years), with 57.4% males. Thirty (63.8%) had NTDT-phenotype, 16 (34%) were asymptomatic/minimally symptomatic, and 1 became transfusion-dependent at the age of 20 years. Anemia/pallor and jaundice were the commonest complaints (76% each); 40% had required blood transfusions. Twenty-one had splenomegaly, 14 had hepatomegaly. Mean hemoglobin was 9.0 ± 1.9 g/dl (range 4.0-13.0). HbA2 was 5.1 ± 0.7% (3.4%-6.3%) and HbF% 4.2 ± 3.2% (0.5%-18.4%). Forty-four (93.6%) had ααα^anti3.7 , while 3 (6.4%) had ααα^anti4.2 triplications. HBB:c.92+5G>C (47%), HBB:c.27_28insG (14.9%), and HBB:c.47G>A (8.5%) were the commonest β-globin mutations. One case showed HBB:c.-138C>T (β⁺⁺ ), while the rest had β⁰ or severe-β⁺ mutations. Symptomatic cases had significantly lower hemoglobins and higher HbF% than asymptomatic ones.

CONCLUSION

This largest Indian and globally second-largest study reports the βTT + ααα^4.2 state for the first time in such genotypically-complex Indian cases. Supernumerary α-genes should be suspected in all βTT with disproportionate clinical symptoms, mild-to-moderately elevated HbF, and unexplained anisopoikilocytosis.

Thalassemia in India

Management and control of hemoglobinopathies are a challenge in India where 67.0% of people reside in rural regions. The GDP spent on health is one of the lowest (1.3%) resulting in high out-of-pocket expenses. The β-thalassemias are prevalent with an estimated 7500-12000 new births each year. Hb S (HBB: c.20A>T) and Hb E (HBB: c.79G>A) are also common regionally. Over 80 β-thalassemia (β-thal) mutations have been characterized in Indians. The δ gene mutations are increasingly being described and their coinheritance in β-thal carriers leads to a reduction in Hb A₂ levels and a misdiagnosis of carriers. Around 15-20 centers offer prenatal diagnosis (PND) mainly in urban regions. The projected annual cost of care of β-thal patients over a decade (2016-2026) will increase from INR30,000 (US$448) million to INR55,000 (US$820) million if all patients are adequately treated. Cost comparisons are difficult to make with other international studies as the standard of care, cost of medicines and other services vary in different countries. Several centers provide hematopoietic stem cell transplants (HSCTs) for thalassemias, however, only around 250 HSCTs are done annually. Although the cost is high, financial assistance is available for a few patients. There are disparities in the quality of care and to address this a National Policy has been proposed for the management and prevention of hemoglobinopathies that will embark on a comprehensive program, providing adequate care and augmenting the existing public health care services. It will also include training, genetic counseling and easier access to preventive options and a National Registry.

Mutational spectrum of thalassemias and other hemoglobinopathies in West Bengal, Eastern India

Thalassemia, an autosomal recessive blood disease, shows a variety of clinical expression in terms of asymptomatic to severe blood transfusion dependence. More than 500 alleles have been characterized in or around the β-globin region. Most of the geographical regions have their own characteristic alleles that predominantly circulate within the communities present in that particular region. In this article, we try to throw some light to explore the spectrum of β-thalassemia (β-thal) alleles present in West Bengal, the eastern part of India. This study comprises thalassemia carriers and diseased persons from different districts of West Bengal. We not only explored the complete mutational spectrum of this state but we also tried to fix the critical range of the values of different hematological parameters [Hb A2, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH)] for the heterozygotes or carriers of β-thal with the same mutational background. At the same time, we also tried to evaluate the maximum weighted frequency of these parameters for the heterozygotes or carriers of β-thal with the same mutational background, so that by observing these cut-off values of standard hematological parameters, we were able to predict the carrier or diseased status for mass scale screening and also try to correlate the values of these parameters with different combinations of β-thal mutation-specific alleles that can be more informative in mass scale (carrier) screening.

Clinicoinvestigational and demographic profile of children with thalassemia major

There are an estimated 200 million carriers of the β-thalassemia gene worldwide, 20 million being in India. The mean prevalence in India is 3.3 %. Objective To evaluate the clinico-investigational profile and the demographic characteristics of patients with thalassemia major (TM). Methods This was a retrospective analysis of the clinico-demographic profile at presentation of patients of TM diagnosed in the Paediatric Hematology Clinic of our hospital. Results The clinical profile of 964 patients of TM was analyzed. The mean age at presentation of untransfused children was 13.2 ± 9.7 months. Nearly 2/3(rd) children presented before 1 year of age. Almost 40 % had symptoms for 3 months prior to presentation. The manifestations at presentation included pallor and failure to thrive. About 40 % presented with severe anemia, with a hemoglobin of <5.0 gm/dl. A large number received blood transfusions prior to establishment of the diagnosis. Half of the families had ancestors who hailed originally from Pakistan. Approximately 50 % belonged to the Khatri/Arora castes. The parental literacy rate was about 90 %. Conclusions Thalassemia needs greater public awareness and prevention strategies in our country. Some communities are at high risk as compared to others. Education programs and compulsory antenatal screening appear to be the order of the day.

Study of Mutations in β-Thalassemia Trait among Blood Donors in Eastern Uttar Pradesh

BACKGROUND

Knowledge on distribution of different mutations of thalassaemia, which are prevalent in a particular area, is a prerequisite for prenatal diagnosis.

OBJECTIVES

Studying mutations in β - thalassaemia trait among blood donors in eastern Uttar Pradesh, India.

MATERIAL AND METHODS

One thousand non - remunerated voluntary blood donors who were between 18 - 40 years of age, were included in the study. Both replacement and voluntary healthy blood donors were included. 4ml of venous blood was collected and it was stored at 4°C. Complete Blood Count (CBC), Haemoglobinopathy Screening and Molecular Analysis by ARMS - PCR (Amplification Refractory Mutation System - PCR) were done. Screening for β thalassaemia was done in a blood bank by using D - 10, Bio Rad, which was based on High Performance Liquid Chromatography (HPLC).

RESULTS

Twenty Eight subjects with β- thalassaemia trait were found among 1000 voluntary blood donors. IVS 1-5 (G-C) mutation was most common type (50%), followed by FS 8/9 (+G) 25% which was the second most common type. In our study, a rare mutation of CD 16 (-C) was also found. Out of 14 subjects who had IVS 1-5 (G-C) mutation (most common), six were from Varanasi (6/261) and five of them were Sindhis. It was seen that FS 41/42 (TCTT) mutation was distributed among all groups of populations which had higher prevalences of β-thalassaemia trait.

CONCLUSION

A comprehensive knowledge on beta thalassaemia mutations is necessary for determining a prenatal diagnosis. The occurrence of mutations may vary according to geographic region. Therefore, this study dealt with current problem of unknown mutations, in order to avoid complications.

Prevalence of β-Thalassemia and hemoglobin E in two migrant populations of Manipur, North East India

Hemoglobinopathies are a group of inherited single-gene disorders found commonly in the Mediterranean region, Middle East, Indian subcontinent, Burma, and South East Asia. As many as 229 mutation variants of β-thalassemia are reported in the world, many community/region-specific mutations. Very little on thalassemia has been reported in Manipur, a North Eastern Indian state. Thus, a community genetic approach through population screening can be applied to the people of Manipur and a total of 602 blood samples from unrelated Meitei Brahmins (n=300) and Meitei Muslims (n=302) were screened for abnormal hemoglobins by Naked Eye Single Tube Red Cell Osmotic Fragility Test (NESTROFT). HBA(2) level was estimated by using high-performance liquid chromatography and molecular analysis was done by using PCR. Sequencing was also carried out to confirm the mutations. High frequencies of NESTROFT positive (10%) and NESTROFT doubtful (11%) cases were found among the Meitei Brahmins in comparison to the Meitei Muslims [NESTROFT positive (3.31%) and NESTROFT doubtful (1.33%)]. The allele frequency of HB*E was 0.022 and 0.012 among the Meitei Brahmin and Meitei Muslim, respectively. Sequencing of the β-globin gene confirmed a very rare β-thalassemia [-90 C→T (0.33%)] among the Meitei Brahmins of Manipur. This mutation with hemoglobin E in one of the present population hints the presence of the Mongoloid stock among them, possibly from China. There is a need for further studies on other populations of Manipur and the neighboring North East Indian states using such genetic markers.

Genetic Heterogeneity of Beta Globin Mutations among Asian-Indians and Importance in Genetic Counselling and Diagnosis

There are an estimated 45 million carriers of β-thalassemia trait and about 12,000–15,000 infants with β-thalassemia major are born every year in India. Thalassemia major constitutes a significant burden on the health care system. The burden of thalassemia major can be decreased by premarital screening and prenatal diagnosis. The success of prenatal diagnosis requires proper knowledge of spectrum of β-thalassemia mutations. In present study, β-thalassemia mutations were characterized in 300 thalassemia cases from 2007 to 2010 using ARMS-PCR and DNA sequencing. The five most common mutations accounted 78.9% of the studied chromosomes that includes IVS1-5(G>C), Cod 41-42(-TCTT), Cod8-9(+G), Cod16(−C) and 619bp del. Though IVS1-5(G>C) is most common mutation in all the communities, the percentage prevalence were calculated on sub caste basis and found that IVS1-5(G>C) percentage prevalence varied from 25 to 60 in Aroras & Khatris and Thakur respectively. Interestingly Cod41-42(−TCTT) mutation which is the second commonest among the mutations reported was totally absent in Kayasthas and Muslim community. These findings have implications for providing molecular diagnosis, genetic counseling and prenatal diagnosis to high risk couples of β-thalassemia.

A new β⁰-thalassemia frameshift mutation [β 48 (-T)] in a Uruguayan family

We describe here a new frameshift mutation of β-thalassemia in a Uruguayan family with Italian ancestry [β48 (-T); HBB:c.146delT]. This frameshift results in formation of premature stop codon (TGA) 40 bp downstream and in a short unstable product that is degraded in the cell.

Molecular basis of β-thalassemia in Karnataka, India

In β-thalassemia, point mutations in the β-globin gene are largely responsible for either decreased or no β-globin synthesis. The β-globin gene has three exons and two introns. The molecular characterization of β-thalassemia is absolutely necessary for carrier screening, for genetic counseling, and to offer prenatal diagnosis. The objective of the present study was to identify the rare mutations in β-globin gene of β-thalassemia patients. We have sequenced the entire β-globin gene in 36 clinically identified thalassemia patients from the Karnataka region using polymerase chain reaction and sequencing. Our analysis revealed 11 β-thalassemia variants. The most common being IVSII-16 G>C, IVSI-5G>C, IVSII-74 T>G, codon 3 (T>C), and Poly A site (T>C). In addition, we have also documented a novel deletion at codon 6 (-CT) (HBB:c.16delCT). These data are useful in future molecular screening of the population for implementing a thalassemia prevention and control program. Further it is found that family studies and comprehensive hematological analyses would provide useful insights for accurate molecular diagnosis of thalassemia phenotype and offers an interesting subject for further investigations in the Indian populations.

Profiling β-thalassaemia mutations in India at state and regional levels: implications for genetic education, screening and counselling programmes

Thalassaemia and sickle cell disease have been recognized by the World Health Organization as important inherited disorders principally impacting on the populations of low income countries. To create a national and regional profile of β-thalassaemia mutations in the population of India, a meta-analysis was conducted on 17 selected studies comprising 8,505 alleles and offering near-national coverage for the disease. At the national level 52 mutations accounted for 97.5% of all β-thalassaemia alleles, with IVSI-5(G>C) the most common disease allele (54.7%). Population stratification was apparent in the mutation profiles at regional level with, for example, the prevalence of IVSI-5(G>C) varying from 44.8% in the North to 71.4% in the East. A number of major mutations, such as Poly A(T>C), were apparently restricted to a particular region of the country, although these findings may in part reflect the variant test protocols adopted by different centres. Given the size and genetic complexity of the Indian population, and with specific mutations for β-thalassaemia known to be strongly associated with individual communities, comprehensive disease registries need to be compiled at state, district and community levels to ensure the efficacy of genetic education, screening and counselling programmes. At the same, time appropriately designed community-based studies are required as a health priority to correct earlier sampling inequities which resulted in the under-representation of many communities, in particular rural and socioeconomically under-privileged groups.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s11568-010-9132-3) contains supplementary material, which is available to authorized users.

Prevalence and molecular characterization of alpha-thalassemia syndromes among Indians

OBJECTIVE

This study was undertaken to determine the prevalence and molecular basis of alpha-thalassemia in the Indian population and its implications in genetic counseling and prenatal diagnosis.

METHODS

1253 random samples were screened for hemoglobinopathies. Red cell indices were measured on the Sysmex K 1000 cell counter; HbA2 and HbF levels were quantitated using high performance liquid chromotography (HPLC). Cellulose acetate electrophoresis and isoelectric focusing (IEF) was done to detect the presence of Hb Bart's in cord blood samples. alpha-Globin gene mapping was done using Southern blot hybridization of BamHI and BglII digests.

RESULTS

Of the 1253 subjects, 132 had a single alpha-gene deletion (10.5%) while 29 had two alpha-gene deletions (2.31%). Fifteen cases showed the presence of alpha-gene triplication (1.1%). A single case showed the presence of one alpha-gene deletion as well as alpha-gene triplication (-alpha/alphaalphaalpha). Overall, the prevalence of alpha-thalassemia was 12.9%. Region-wise and caste-wise analysis showed the highest prevalence of alpha-thalassemia among the Punjabi population originating from the northern region of India.

CONCLUSION

alpha-Thalassemia is by far the commonest hemoglobinopathy in India, but it is not a cause of serious genetic risk is the milder form (-alpha/alphaalpha) of alpha-thalassemia, which is predominant. Knowing the alpha-genotype is useful for genetic counseling for prenatal diagnosis in couples where one of the parents may have reduced indices coupled with a raised RBC count and normal HbA2 levels.

Analysis of beta globin mutations in the Indian population: presence of rare and novel mutations and region-wise heterogeneity

Beta thalassaemia is a major public health problem in India. A comprehensive database of the spectrum of mutations causing beta thalassaemia in the Indian population is necessary. This study in which a large number of patients with beta thalassaemia including those from certain regions that were not explored earlier shows a great heterogeneity of mutations. Several novel and rare alleles that have not been reported earlier in the Indian population have been identified, and mutations differ in frequency in different regions of the country. This information on the spectrum of mutations has implications for the control of beta thalassaemia in a population with complex ethnic background and also on the genotype-phenotype correlation of the disease.

The clinical significance of the spectrum of interactions of CAP+1 (A→C), a silent β-globin gene mutation, with other β-thalassemia mutations and globin gene modifiers in north Indians

OBJECTIVES

To assess the clinical significance of the interactions of CAP+1 (A-->C), a silent beta-globin gene mutation, with other beta-thalassemia mutations and globin gene modifiers in north Indians.

METHODS

The clinical phenotypes associated with compound heterozygosity for the CAP+1 (A-->C) mutation with other beta-thalassemia mutations, together with the potential effect of the genetic modifiers alpha-thalassemia and the Xmn-1(G)gamma C-->T polymorphism were studied in 30 patients. The frequency of the CAP+1 (A-->C) polymorphism was determined and an analysis of the red cell indices, HbA(2) levels, iron status, and alpha-globin genes was carried out in 35 heterozygotes.

RESULTS

Based on an analysis of 1075 beta-thalassemia alleles the CAP+1 (A-->C) mutation constituted 3.2% of north Indians. There was a wide spectrum of phenotypic severity in compound heterozygotes; 18 of 30 were transfusion dependent. There was a very high frequency of the -/- genotype of the Xmn-1(G)gamma polymorphism in compound heterozygotes. Analysis of 35 heterozygotes indicated that approximately half were hematologically normal and therefore genuine 'silent' carriers.

CONCLUSIONS

Compound heterozygotes for CAP+1 (A-->C) and other severe beta-thalassemia alleles are phenotypically severe enough to necessitate appropriate therapy and counseling. The unexpected severity of these interactions may be due, in part, to the high frequency of beta-thalassemia alleles associated with the Xmn-1(G)gamma- allele in Indian populations. It is concluded that the CAP+1 (A-->C) mutation can pose serious difficulties in screening and counseling programs in populations in which it occurs at a significant frequency.

Nucleotide -88 (C-T) promoter mutation is a common beta-thalassemia mutation in the Jat Sikhs of Punjab, India

A study of beta-gene mutations in Jat Sikhs, a subcaste of Punjabis, revealed a very high prevalence (46%: 41/88) of the mild beta++ promoter region mutation -88 (C-T). Sixteen individuals presenting in homozygous form were clinically mild. Un-transfused patients had characteristic hematological findings: high Hb F (38.1-68.6%, mean 47.4%), high Hb A2 (5.7-9.8%, mean 6.88%), and the rest had adult hemoglobin. The 19 subjects with compound heterozygosity for -88 (C-T) and another beta-gene mutation presented both as thalassemia intermedia (four cases) and as thalassemia major (15 cases). One of the four patients with the milder phenotype had a second mild mutation, CAP+1 (beta++). In the other three cases with the milder phenotype, the second mutation was associated with the presence of the XmnI Ggamma polymorphism. Notably, the XmnI Ggamma was negative in all the -88 (C-T) alleles. None of the patients had associated alpha-thalassemia even in the thalassemia intermedia group. Haplotype analysis of the -88 (C-T) homozygous cases showed a single haplotype (+ - - - - + -) in all but two individuals. This haplotype is distinct from those described in the Africans with homozygous -88 (C-T), suggesting that the mutation in our population occurred independently.

Molecular genetic analyses of β-thalassemia in South India reveals rare mutations in the β-globin gene

beta-Thalassemia is the most prevalent single-gene disorder. Since no viable forms of treatment are available, the best course is prevention through prenatal diagnosis. In the present study, the prevalence of beta-thalassemia was extensively investigated in the South Indian population, especially from the state of Andhra Pradesh. Screening for causal mutations was carried out on genomic DNA isolated from patient blood samples by using the routine reverse dot blot (RDB) and amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) techniques. DNA sequencing was performed wherever necessary. Among the nine mutations identified, four, including IVS-1-5 (G-C) (IVS1+5G>T), codon 41/42 (-TTCT) (c.124_127delTTCT), codon 15 (G-A) (c.47G>A), and HbS (sickle mutation) (c.20A>T) mutations, accounted for about 98% of the total positive cases. Two mutations viz. codon 8/9 (+G) (c.27_28insG) and HbE (codon 26 G-A) (c.79G>A) exhibited a very low frequency of occurrence, whereas the IVS-1-1 (G-T) (IVS1+1G>T) and the 619 bp deletion (c.366_494del) mutations were absent. We also identified certain rare mutations during the diagnostic evaluation. Gene sequencing confirmed the codon 30 (G-C) (c.92G>C) mutation and the rare codon 5 (-CT) (c.17_18delCT) and IVS-II-837 (T-G) (IVSII-14T>G) mutations. This is the first report of the IVS II 837 mutation in the Indian population. We also report a novel diagnostic application during RDB-based screening for the detection of the (c.92G>C) mutations. Such a comprehensive mutation screening is essential for prenatal diagnosis of beta-thalassemia and control of this highly prevalent monogenic disorder in the Indian population.

High frequency of deletional alpha-thalassemia in beta-thalassemia trait: implications for genetic counseling

Thalassemias are a group of genetic hemolytic disorders with varying phenotypes. In this study, the frequency of alpha globin gene deletions was studied in the beta-thalassemia trait, the mildest form of the disorder. Eleven out of 33 (33%) individuals were positive for alpha(-3.7 kb) deletions. None of the subjects was positive for the Southeast Asian deletion. Such a high frequency for alpha deletions has not been reported earlier in thalassemia minor. Hematological parameters are compared, and implications of this finding for genetic counseling are discussed.

Molecular genetic testing of beta-thalassemia patients of Indian origin and a novel 8-bp deletion mutation at codons 36/37/38/39

Hemoglobinopathies are the most commonly inherited genetic disorders in India. Certain communities in India have a high predisposition to beta-thalassemia. To offer prenatal diagnosis and to prevent the birth of an affected child, mutation testing in clinically diagnosed beta-thalassemia patients/carriers is a prerequisite. Over a period of 4 years, we have conducted DNA analysis in 385 carriers for 15 beta-thalassemia mutations, HbD, HbE, and HbS. Using reverse dot blot (RDB) and amplification refractory mutation system (ARMS), we have been able to identify mutations in 381 of 385 thalassemia chromosomes. The study included the analysis of five common mutations found in Asian Indians, namely IVS1-5 (G-C), 619-bp deletion, IVS1-1 (G-T), and the frameshifts at CD8/9(+G) and CD41/42(-CTTT). The occurrence of these five mutations was seen in 299 (91.2%) carriers referred to us, the percentage of mutations varying between 4.0 and 68.9%. We also found Cd16 (-C) in 2.1%, CD30 (G-C) in 1.5%, and CD 15(G-A) in 0.6%; these are considered common mutations in the Indian population, as well. The beta-thalassemia anomaly in 4 (0.6%) carriers remained uncharacterized by RDB and ARMS analysis. During delineation of the mutations in uncharacterized carriers by single-stranded conformational polymorphism (SSCP) and sequencing analysis, we have also been able to identify two unusual mutations, one involving an initiation codon and the second involving a novel 8-bp deletion, in Indian families of Uttar Pradesh origin.

Molecular characterization of alpha-thalassemia in Pakistan

Common alpha-thalassemia (thal) rearrangements were studied in a normal random population and in six ethnic groups of Pakistan. Analyses of 204 individuals from the normal population revealed the presence of only the -alpha(3.7) allele with an overall frequency of 8.3%. Ethnic differences were statistically significant for Pashtoon vs. Balochi (p < 0.0005) and Pashtoon vs. Sindhi (p < 0.002). Two hundred and eighty-five thalassemia patients were also studied to identify rare alpha-thal alleles. In this group, 24.6% of the patients had one or two alpha genes deleted. Two rare alleles in the Pakistani population, -alpha(4.2) (0.2%) and alphaalphaalpha(anti3.7) (0.9%), were identified in these patients. The -alpha(4.2) allele was found only in Sindhis, while alphaalphaalpha(anti3.7) was present in Punjabis, Sindhis and Balochis. Five patients with triplicated alpha genes were homozygous for either the beta+ or the beta(0) genotype.

A novel beta0-thalassemia mutation at codon 55 (-A) and a rare 17 bp deletion at codons 126-131 in the Indian population

A new mutation at codon 55 (-A) and a rare mutation, a 17 bp deletion at codons 126-131, that gives rise to beta0-thalassemia, were found in the Indian population by means of direct sequencing of two polymerase chain reaction products generated from a 2.3 kb DNA fragment containing the whole beta-globin gene. Each polymerase chain reaction product was sequenced on both strands in a mutation-loading format, showing all nucleotide substitutions or deletions/insertions, including mutations and polymorphisms, in the product. The entire protocol requires four sequencing reactions/gel loadings after two successive polymerase chain reactions, which simplifies the mutation search process and reduces the reading error rate.

Rare beta-thalassemia mutations in Asian Indians

Among 365 carriers of beta-thalassemia, 13 subjects remained uncharacterized after ARMS analysis. Among these 13 individuals, 8 mutations were identified by direct sequencing of the PCR-amplified product, which have not been described in Asian Indians earlier. These included (1) T-C substitution at IVS II position 591, a new beta-thalassemia mutation which probably creates an alternative donor splice site in antisense strand; (2) the mutations CoD4 (T-A), CoD5 (C-T), CoD6 (G-T) at cis location; (3) CoD13 (C-T), CoD26 (G-A), CoD 27/28(-C) at cis location; (4) CoD 8 (A-G); (5) CoD30 (G-C); (6) CoD5 (-CT); (7) IVSI-1 (G-A); and (8) FS47/48 (+ATCT). The latter four have been described in other populations but are identified in Asian Indians for the first time. This completes the characterization of beta-thalassemia mutations in 365 carriers of Asian Indian origin, enabling us to provide a comprehensive prenatal diagnosis of beta-thalassemia in our population.

Distribution of beta-thalassemia mutations in the Indian population referred to a diagnostic center

Hemoglobinopathies are the most commonly inherited genetic disorders in India. Population screening has identified certain communities in India with high risk of beta-thalassemia, the prevalence of carrier status in some being as high as 17%. Over a period of 6 years we have conducted DNA analysis on 1,233 carriers of 23 beta-thalassemia mutations and Hb E, using the amplification refractory mutation system. The studies included analyses of five common mutations for Asian Indians, namely IVS-I-5 (G-->C), 619 bp deletion, IVS-I-1 (G-->T), and the frameshifts at codons 8/9 (+G) and 41/42 (-TTCT). The occurrence of these was seen in 1,066 (86.45%) of the carriers referred to us, the percentage of mutations varying between 5.03-42.58%. We found codon 15 (TGG-->TAG) in 47 (3.81%) samples which was also considered a common mutation in the Indian population. Rare beta-thalassemia mutations were found in 87 (7.06%) individuals. We have designed five new primers and modified four primers for nine rare mutations. These were seen in nine (0.73%) samples. The beta-thalassemia anomaly in 33 (2.68%) carriers remained uncharacterized. State-wide and community-wide distribution patterns of mutations indicated that IVS-I-5 (G-->C) is the most common beta-thalassemia allele in the Indian population. Sindhis settled in Gujrat, and Maharashtra and Lohanas from Gujrat showed a prevalence of the 619 bp deletion mutation in 49.2 and 45.5% carriers, respectively. High frequency of the IVS-I-1 (G-->T) mutation was also found in Sindhis (25.5%), Punjabi Hindus (34.7%), and Lohanas (31.2%). These studies of mutation patterns in different communities have helped us in the quick identification of beta-thalassemia mutations for prenatal diagnosis.

Geographic and ethnic distribution of beta-thalassemia mutations in Uttar Pradesh, India

We have studied the geographic and ethnic distribution of mutations in 376 subjects who were carriers of beta-thalassemia, and identified the mutations in 365 chromosomes. The majority of the beta-thalassemia carriers were of Uttar Pradesh (India) origin. Their pattern of mutations differed from the other states of India and from those families who had migrated from Pakistan. The frequency of the IVS-I-5 (G-->C) and 619 bp deletion mutations were 64.3 and 2.5%, respectively, among families originating from Uttar Pradesh, compared to a prevalence of 37.5 and 27.5%, respectively in the population of Pakistani immigrants. Of the 10 common Asian Indian mutations, only eight were observed in subjects studied from different parts of India. By use of the amplification refractory mutation system along with DNA sequencing techniques, the mutations were successfully identified in 97.1% of subjects, while 11 cases (2.9%) still remain to be characterized by single strand conformation polymorphism and sequencing analyses. The application of this knowledge has facilitated the successful implementation of the program of genetic counseling and prenatal diagnosis of beta-thalassemia, thus helping to avoid the birth of an affected child in India.

Potential of denaturing gradient gel electrophoresis for scanning of beta-thalassemia mutations in India

Over the last few years, substantial progress has been made in developing strategies for the detection and characterization of various mutations causing beta-thalassemia. The Indian population comprises of numerous endogamous caste groups and beta-thalassemia is seen in almost all of them. Knowledge of the spectrum of beta-thalassemia mutations in the population is a prerequisite for successful implementation of a prevention programme. Among the different approaches available today, Denaturing Gradient Gel Electrophoresis (DGGE) offers a valid technical approach which is applicable for screening of known mutants and polymorphisms as well as in locating regions of DNA bearing unknown mutations. We analysed 356 unrelated beta-thalassemia heterozygotes by DGGE and detected 30 anomalous DGGE patterns. Fifteen mutations were characterized after sequencing 25 anomalous patterns. Of these, codon 10(GCC --> GCA) is a recently reported novel beta-thalassemia mutation while -28(A --> G) and codon 121(G --> T) are being reported for the first time in the Indian population. HbS and HbE also showed two anomalous DGGE patterns each. Framework (FW) linkage studies showed that four mutations were associated with different beta-globin gene frameworks. Linkage of IVSI-5(G --> C) and cap site +1(A --> C) to FW2 and 619-bp deletion to FW1 is being observed for the first time. Multiple DGGE patterns corresponding to the same mutation is one of the major drawbacks of this technique. In spite of this, if sufficient preliminary work has been carried out to compile a comprehensive catalogue of DGGE patterns; this is a powerful approach to characterize the mutation or to localize a small region of DNA in the case of rarer mutations.

Beta-thalassemias: expression, molecular mechanisms and mutations in Indians

The beta-thalassemias are a heterogenous group of inherited disorders of hemoglobin (Hb) synthesis characterized by a reduction (beta+) or absence (beta zero) of synthesis of the beta globin chains of Hb, resulting in an imbalanced chain synthesis. To understand their expression and molecular basis in Indians, it is essential to review briefly the genetic control of normal Hb production and the structure, organization and regulation of different globin genes. The Indian beta-thalassemia mutations and strategies for prevention are described.

The population genetics of the haemoglobinopathies

The haemoglobinopathies are the commonest single-gene disorders known, almost certainly because of the protection they provide against malaria, as attested by a number of observations. The geographical distributions of malaria and haemoglobinopathies largely overlap, and microepidemiological surveys confirm the close relationship between them. For two of the commonest disorders, haemoglobin S and alpha(+)-thalassaemia, there is also good clinical evidence for protection against malaria morbidity. However, not all the evidence appears to support this view. In some parts of the world malaria and haemoglobinopathies are not, and never have been, coexistent. It is also difficult to explain why the majority of haemoglobinopathies appear to be recent mutations and are regionally specific. Here we argue that these apparent inconsistencies in the malaria hypothesis are the result of processes such as genetic drift and migration and of demographic changes that have occurred during the past 10,000 years. When these factors are taken into account, selection by malaria remains the force responsible for the prevalence of the haemoglobinopathies.

Prenatal diagnosis of beta-thalassemia among Indians using denaturing gradient gel electrophoresis

We have offered first trimester prenatal diagnosis to 55 couples at risk for beta-thalassemia, originating from various parts of India, using polymerase chain reaction and denaturing gradient gel electrophoresis. Apart from the six common mutations, codon 30 (CAG-->CAA), Cap site +1 (A-->C), as well as three uncharacterized mutations were seen among the parents. In the majority of cases, the diagnosis was possible by scanning only one fragment (B) where most of the Indian mutations are situated. In 18 out of 55 cases, framework analysis could also have been used to offer prenatal diagnosis without characterizing the beta-thalassemia mutations. In the two cases where the mutations were uncharacterized, prenatal diagnosis was done only on the basis of the anomalous denaturing gradient gel electrophoresis patterns seen in the parents and in previously affected children. This is the first attempt of prenatal analysis using denaturing gradient gel electrophoresis in the extremely diverse Indian population where the profile of mutations has not yet been fully elucidated.

Different hematological phenotypes caused by the interaction of triplicated alpha-globin genes and heterozygous beta-thalassemia

The pathophysiology and clinical severity of beta-thalassemia are related to the degree of alpha/non-alpha-chain imbalance. A triplicated alpha-globin gene locus can exacerbate effects of excess alpha-chains caused by a defective beta-globin gene, although this is not observed in all cases. Extensive studies on this condition are lacking. We report a group of 17 patients who are heterozygous for both the alpha alpha alpha(anti-3.7) allele and a mutation in the beta-globin gene cluster. Their clinical phenotypes varied: six had mild anemia with microcytosis and hypochromia, while 11 had more severe anemia with splenomegaly requiring splenectomy (three cases) and blood transfusions (four cases). Different phenotypes were also evident in the presence of the same beta-thalassemia mutation: in one family, two individuals had the same alpha- and beta-globin genotypes but presented with different hematologic phenotypes. In addition, the complex interaction involving a triplicated alpha-globin gene, beta39- and delta+27-thalassemia mutations is studied in a family with two siblings presenting with hemolytic anemia, normal Hb A2 and increased Hb F. Analysis of this series of patients suggests that additional genetic determinants play a role in modulating phenotypic expression in individuals with identical alpha- and beta-globin genotypes. Interaction with a triplicated alpha-gene can play a role in the clinical presentation of patients with defective beta-globin gene expression and should be considered in the diagnosis of atypical cases.

A significant beta-thalassemia heterogeneity in the United Arab Emirates

The Dubai Thalassemia Center has identified 35 different beta-thalassemia mutations in 570 chromosomes from the United Arab Emirates population using gene amplification, hybridization with specific labeled oligonucleotide probes, sequencing of amplified DNA, restriction enzymes, and amplification refractory mutation system techniques. This large number of mutations which represent 21% of the total beta-mutations discovered worldwide reflects the heterogenous nature of the population living in the United Arab Emirates (1). We found that 50% of our beta-thalassemia patients have a concomitant alpha-thalassemia; namely the -alpha 3.7 kb deletion. Co-inheritance of alpha-thalassemia especially in the form of two alpha-globin gene deletions have an ameliorating effect on the phenotype presentation of our beta-thalassemia. Nine patients (one homozygote and eight compound heterozygotes) were identified with Hb Monroe (IVS-I,-1 (G-->C)), a thalassemic hemoglobin characterized by an Arg-->Thr substitution in codon 30 of the beta-globin gene. In addition, one of the patients was a compound heterozygote for Hb Tacoma [IVS-I, +1 (G-->C)]; a point mutation affecting the third nucleotide of codon 30 (G-->C) causing an Arg-->Ser replacement.

A novel frameshift mutation causing beta-thalassemia in a Sikh

During our survey of beta-thalassemia mutations among residents of the United Arab Emirates, we came across a Sikh family who had two new beta-thalassemia mutations. The father had a frameshift mutation at codons 47/48 (+ATCT), and the mother another frameshift mutation at codons 57/58 (+C). The offspring of this family were two daughters with beta-thalassemia trait and a boy with a compound heterozygosity. The boy, who was transfusion-dependent from the age of 7 months, had a successful bone marrow transplant from his eldest sister at the age of 13 months.

Beta-thalassemia intermedia in a Lebanese child due to homozygosity for the -88 (C-->T) mutation

We report a case of beta-thalassemia intermedia involving a 3-year-old male child of Lebanese descent. Molecular studies of the family showed that he is homozygous for the -88 (C-->T) beta (+)-thalassemia mutation. This mutation is the second most common cause of beta-thalassemia in Black populations, and has also been reported in Asian Indians. A review of Lebanese beta-thalassemia cases revealed considerable mutation heterogeneity and excess homozygosity due to consanguinity.