Prevalence and Distribution of Major ß-Thalassemia Mutations and HbE/ß-Thalassemia Variant in Nepalese Ethnic Groups.

BACKGROUND: Beta-thalassemia is a genetic disorder that is inherited in an autosomal recessive pattern. This genetic disease leads to a defective beta-globin hemoglobin chain causing partial or complete beta-globin chain synthesis loss. Beta-thalassemia major patients need a continuous blood transfusion and iron chelation to maintain the normal homeostasis of red blood cells (RBCs) and other systems in the body. Patients also require treatment procedures that are costly and tedious, resulting in a serious health burden for developing nations such as Nepal. METHODS: A total of 61 individuals clinically diagnosed to have thalassemia were genotyped with multiplex amplification refractory mutation system-polymerase chain reaction (ARMS-PCR). Twenty-one major mutations were investigated using allele-specific primers grouped into six different panels. RESULTS: The most common mutations found (23%) were IVS 1-5 (G-C) and Cd 26 (G-A) (HbE), followed by 619 deletion, Cd 8/9 (+G), Cd 16 (-C), Cd 41/42 (-TTCT), IVS 1-1 (G-T), Cd 19 (A-G), and Cd 17 (A-T) at 20%, 12%, 8%, 6%, 4%, 3%, and 1%, respectively. CONCLUSION: The results of this study revealed that Nepal's mutational profile is comparable to that of its neighboring countries, such as India and Myanmar. This study also showed that thalassemia could be detected across 17 Nepal's ethnic groups, especially those whose ancestors originated from India and Central Asia.

Genetic polymorphisms of HbE/beta thalassemia related to clinical presentation: implications for clinical diversity.

HbE/Beta thalassemia (HbE/ß-thalassemia) is one of the common genetic disorders in South East Asia. It is heterogeneous in its clinical presentation and molecular defects. There are genetic modifiers which have been reported to influence the disease severity of this disorder. The aim of this study was to determine the genetic polymorphisms which were responsible for the disease clinical diversity. A case-control study was conducted among Malay transfusion-dependent HbE/ß-thalassemia patients. Patients who were confirmed HbE/ß-thalassemia were recruited and genotyping study was performed on these subjects. Ninety-eight patients were selected and divided into moderate and severe groups based on clinical parameters using Sripichai scoring system (based on hemoglobin level, spleen size, growth development, the age of first transfusion and age of disease presentation). Forty-three (44.9%) and 55 (56.1%) patients were found to have moderate and severe clinical presentation, respectively. Genotyping analysis was performed using Affymetrix 6.0 microarray platform. The SNPs were filtered using PLINK and Manhattan plot by R software. From the GWAS results, 20 most significant SNPs were selected based on disease severity when compared between moderate and severe groups. The significant SNPs found in this study were mostly related to thalassemia complications such as rs7372408, associated with KCNMB2-AS1 and SNPs associated with disease severity. These findings could be used as genetic predictors in managing patients with HbE/ß-thalassemia and served as platform for future study.

Rapid Targeted Next-Generation Sequencing Platform for Molecular Screening and Clinical Genotyping in Subjects with Hemoglobinopathies.

Hemoglobinopathies are among the most common autosomal-recessive disorders worldwide. A comprehensive next-generation sequencing (NGS) test would greatly facilitate screening and diagnosis of these disorders. An NGS panel targeting the coding regions of hemoglobin genes and four modifier genes was designed. We validated the assay by using 2522 subjects affected with hemoglobinopathies and applied it to carrier testing in a cohort of 10,111 couples who were also screened through traditional methods. In the clinical genotyping analysis of 1182 ß-thalassemia subjects, we identified a group of additional variants that can be used for accurate diagnosis. In the molecular screening analysis of the 10,111 couples, we detected 4180 individuals in total who carried 4840 mutant alleles, and identified 186 couples at risk of having affected offspring. 12.1% of the pathogenic or likely pathogenic variants identified by our NGS assay, which were undetectable by traditional methods. Compared with the traditional methods, our assay identified an additional at-risk 35 couples. We describe a comprehensive NGS-based test that offers advantages over the traditional screening/molecular testing methods. To our knowledge, this is among the first large-scale population study to systematically evaluate the application of an NGS technique in carrier screening and molecular diagnosis of hemoglobinopathies.

Multiplex amplification refractory mutation system (MARMS) for the detection of ß-globin gene mutations among the transfusion-dependent ß-thalassemia Malay patients in Kelantan, Northeast of Peninsular Malaysia.

The aim of this study was to adapt MARMS with some modifications to detect beta mutation in our cohort of thalassemia patients. We focused only on transfusion-dependent thalassemia Malay patients, the predominant ethnic group (95%) in the Kelantanese population. Eight mutations were identified in 46 out of 48 (95.83%) beta thalassemia alleles. Most of the patients (54.2%) were compound heterozygous with co-inheritance Cd 26 (G>A). The frequencies of spectrum beta chain mutation among these patients are presented in Table 2. Among the transfusion dependent beta thalassemia Malay patients studied, 26 patients were found to be compound heterozygous and the main alleles were Cd 26 (G>A). Compound heterozygous mutation of Cd 26 (G>A) and IVS 1-5 (G>C) were 12 (46.2%), Cd 26 (G>A) and Cd 41/42 (TTCT) were 9 (34.6%), Cd 26 (G>A) and IVS 1-1 (G>C) were 2 (7.7%) respectively. Meanwhile the minority were made of a single compound heterozygous of Cd 26 (G>A) and Cd 71/72, Cd 26 (>A) and Cd 17 (A>T), Cd 26 (G>A) and -28 (G>A) respectively. Twenty out of forty six patients were shown to have homozygous of IVS 1-5 (G>C) were 2 (10.0%), Cd 26 (G>A) were 15 (75.0%), Cd 19 (A>G) were 1 (5.0%), and IVS 1-1 (G>T) were 2 (10.0%). The beta chain mutations among the Kelantanese Malays followed closely the distribution of beta chain mutations among the Thais and the Malays of the Southern Thailand. The G-C transition at position 5 of the IVS 1-5 mutation was predominant among the Malay patients. In conclusion, this method has successfully identified the mutation spectrum in our cohort of transfusion-dependent beta thalassemia patients, and this method is equally effective in screening for mutation among thalassemia patients.