Rare beta-thalassemia mutations in Asian Indians

The Prevalence Of β-Thalassemia Mutations in South Western Maharashtra

Thalassemia has been recognized by the World Health Organization as important inherited disorders principally impacting on the populations of low income countries. In this report, the prevalence of common β-thalassemia mutations in India was defined in 126 β-thalassemia carrier subjects in a western Indian population mainly from the south-western Maharashtra. The six most common β-thalassemia mutations were detected, which included IVS I-5 (G-C), IVS I-1 (G-T), codon 8-9 (+G), codon 41/42 (-TCTT), Codon 15 (G-A), and 619 bp deletion at 3' end of β-globin gene. These mutations accounted for 93.66 % in 126 β-thalassemia carrier subjects and 6.34 % remained uncharacterized. Out of 126, 82 (65.07 %) showed the most common (prevalent) type of mutation, IVS I-5 (G-C), followed by IVS I-1 (G-T) showed by 12 (9.52 %) subjects. Three (2.38 %) subjects showed 619 bp deletion, codon 8/9 (+G) and codon 15 (G-A) mutations were present in eight subjects each (6.34 %). Only five (3.96 %) subjects showed codon 41/42 (-TCTT). There were eight (6.34 %) subjects where mutation was not any of the six mutations studied. This study provides the pattern of β thalassemia mutations from south-western Maharashtra, which will help to prevent β-thalassemia using prenatal diagnosis and proper counseling.

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.

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

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Hematological and molecular analysis of novel and rare beta-thalassemia mutations in the Indian population

A variety of mutations causing beta-thalassemia (beta-thal) have been seen in the Indian subcontinent. We report eight families in whom two novel mutations [codon 16 (C>T), IVS-II-613 (C>T)] and three rare mutations [codons 22/23/24 (-7 bp) (-AAGTTGG), -87 (C>A), codon 15 (-T)] were encountered among 375 beta-thal heterozygotes. They were referred to us for molecular characterization or prenatal diagnosis during a period of 2 years. Haplotyping was also done for linkage analysis.

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.

Initiation codon mutation in an Asian Indian family

The beta-thalassemias are a heterogeneous group of hereditary anemias. A multitude of mutations have been reported, resulting in varied phenotypes. In each ethnic group there is always a subset of common, less common, and rare mutations, which makes population screening, prenatal diagnosis, and genetic counseling easier. In this paper we report a rare beta-thalassemia mutation found in an Indian subject by SSCP and sequencing analysis. The mutation, initiation ATG --> ACG, was found in heterozygous condition in a patient belonging to Brahmin family of Uttar Pradesh origin. Haplotype analysis was performed to identify the chromosomal background associated with the mutation and to tracing the origin and spread of the mutation. This study, as previous studies, suggests that rare beta-thalassemia mutations, such as the initiation codon mutations, have no set geographical distribution and are relatively recent.