Thalassaemia-like carriers not linked to the beta-globin gene cluster

Genetic determinants of β-thalassemia intermedia in Pakistan

This study covers the molecular characterization of clinically diagnosed β-thalassemia intermedia (β-TI) patients in Pakistan. Blood samples of β-TI patients were collected from all four provinces of Pakistan throughout the period of 2011-2013. The study was carried out using allele-specific primers through polymerase chain reaction or sequencing to determine both α- and β-thalassemia (α- and β-thal) mutations, and restriction enzymes for the characterization of β-globin gene arrangements. In a total of 63 patients, the IVS-I-5 (G > C) was the most frequent mutation (33.88%). The codon 30 (G > A) and IVS-II-1 (T > C) mutations were found only in the Punjabi ethnic group, while the codon 30 (G > C) and Hb S (HBB: c.20A > T) mutations were found only in the Pashtoon and Sindhi ethnic groups, respectively. In case of α-globin genotypes, 44 patients were normal (αα/αα), six patients carried the αα/-α(3.7) genotype, 12 patients carried the -α(3.7)/-α(3.7) genotype, while one patient had the αα/ααα(anti 3.7) genotype. We found that haplotype I was the most frequent, mostly associated with the codons 8/9 (+G) mutation, while the Saudi haplotype was found only with Hb S.

The modifying effect of Xmn1-HBG2 on thalassemic phenotype is associated with its linked elements in the beta globin locus control region, including the palindromic site at 5'HS4

The core sequence of 5'HS4-beta globin locus control region and Xmn1-HBG2 site were analyzed and compared among 86 thalassemia patients with homozygous or compound heterozygous beta globin gene mutations and 101 normal individuals. Frequency of the G allele in the polymorphic palindromic sequence of 5'HS4 (TGGGG A/G CCCCA) and positive Xmn1-HBG2 profile was significantly higher in thalassemia patients compared to the normal population. Linkage disequilibrium was observed between the G allele and positive Xmn1-HBG2 profile in patient population. Furthermore, dominance of IVSII-1 in the mutation spectrum of the patients enabled us to identify linkage disequilibrium relationships between IVSII-1, positive Xmn1-HBG2 and the G allele at 5'HS4. The frequency of milder clinical phenotype was significantly higher in patients with GG/++ than cases with AA/-- genotypic pattern in 5'HS4/Xmn1-HBG2 loci. These data together with biochemical evidence suggesting a role for the A/G polymorphism at 5'HS4 palindromic site on modifying chromatin structure and in the absence of any evidence from functional studies relating the Xmn1-HBG2 site to the increased gamma chain expression, suggest that the phenotype modifying role long time assigned to Xmn1-HBG2 is possibly played by more functionally potent elements linked to it in LCR.

Association of α globin gene quadruplication and heterozygous β thalassemia in patients with thalassemia intermedia

Ten patients with thalassemia intermedia with variable severity and apparent simple heterozygosis for beta0 39 C>T nonsense mutation were submitted to clinical, hematologic and molecular studies. The presence of an unknown molecular defect (silent beta-thalassemia) unlinked to the beta cluster interacting with the heterozygous beta thalassemia, was previously postulated in these families. Analysis of the alpha globin gene cluster with PCR-based methods (MLPA, GAP-PCR, digestion with restriction enzymes) detected complex rearrangements in the alpha cluster. A duplication of the alpha globin gene locus, including the upstream regulatory region, was present in all the patients, associated in some of them with deletion or non-deletion alpha thalassemia. The variability of the clinical phenotype correlates with the degree of the globin chain imbalance. The presence of alpha globin cluster duplication should be considered in patients heterozygote for beta-thalassemia with thalassemia intermedia phenotype and in the carriers of suspected silent beta thalassemia.

The molecular basis of beta-thalassemia intermedia in southern China: genotypic heterogeneity and phenotypic diversity

Background

The clinical syndrome of thalassemia intermedia (TI) results from the β-globin genotypes in combination with factors to produce fetal haemoglobin (HbF) and/or co-inheritance of α-thalassemia. However, very little is currently known of the molecular basis of Chinese TI patients.

Methods

We systematically analyzed and characterized β-globin genotypes, α-thalassemia determinants, and known primary genetic modifiers linked to the production of HbF and the aggravation of α/β imbalance in 117 Chinese TI patients. Genotype-phenotype correlations were analyzed based on retrospective clinical observations.

Results

A total of 117 TI patients were divided into two major groups, namely heterozygous β-thalassemia (n = 20) in which 14 were characterized as having a mild TI with the Hb levels of 68-95 g/L except for five co-inherited ααα^anti-3.7 triplication and one carried a dominant mutation; and β-thalassemia homozygotes or compound heterozygotes for β-thalassemia and other β-globin defects in which the β⁺-thalassemia mutation was the most common (49/97), hemoglobin E (HbE) variants was second (27/97), and deletional hereditary persistence of fetal hemoglobin (HPFH) or δβ-thalassemia was third (11/97). Two novel mutations, Term CD+32(A→C) and Cap+39(C→T), have been detected.

Conclusions

Chinese TI patients showed considerable heterogeneity, both phenotypically and genotypically. The clinical outcomes of our TI patients were mostly explained by the genotypes linked to the β- and α-globin gene cluster. However, for a group of 14 patients (13 β⁰/β^N and 1 β⁺/β^N) with known heterozygous mutations of β-thalassemia and three with homozygous β-thalassemia (β⁰/β⁰), the existence of other causative genetic determinants is remaining to be molecularly defined.

Disease knowledge and treatment adherence among patients with thalassemia major and their mothers in Taiwan

AIMS

The current study had three aims: (i) to examine disease knowledge in both thalassemia major patients and their mothers; (ii) to understand the relationships between disease knowledge and treatment adherence in thalassemia major patients; and (iii) to explore the importance of selected factors in predicting patients' knowledge about thalassemia major.

BACKGROUND

Patients with thalassemia major must be treated with life-long blood transfusions. Evidence suggests that patients with more knowledge/information about their illnesses adhere more readily to treatment schedules. However, there has been little evaluation of knowledge and treatment adherence in thalassemia major patients.

DESIGN AND METHODS

A cross-sectional correlational survey design and purposive sampling were used. Thirty-two thalassemia major patients (mean age 17.5 years) and 32 mothers (mean age 40.5 years) were recruited.

RESULTS

On a scale ranging from 0-20, the average of the patients' disease knowledge about thalassemia major was 15.19 and the average of their mothers' disease knowledge was 16.44. The scores for the patients' disease knowledge about thalassemia major were positively correlated with follow-up visit adherence (r = 0.690, p < 0.001) and with desferrioxamine infusion adherence (r = 0.791, p < 0.001). 95.6% of variance in patients' knowledge was explained by a model that included mothers' knowledge (beta = 0.901, p < 0.001), follow-up visit adherence (beta = 0.084, p = 0.140) and annual household income (beta = 0.042, p < 0.387).

CONCLUSIONS

The positive association between knowledge and treatment adherence and factors of patients' knowledge indicate the need for systematic education for patients and caregivers to improve adherence to treatment.

RELEVANCE TO CLINICAL PRACTICE

Improvement of the quality of patient care, reinforcement of medical education and enhanced efforts by clinical staff to provide practical knowledge to patients with thalassemia major should significantly improve patient adherence to treatment.

Molecular mechanisms underlying thalassemia intermedia in Iran

To improve the differentiation of thalassemia intermedia from other hemoglobinopathies in Iran, four known genetic mechanisms-XmnI (G)gamma polymorphism, inheritance of mild and silent beta-thalassemia alleles, delta beta deletion, and coinheritance of alpha- and beta-thalassemia-were investigated in 52 Iranian individuals suspected to have thalassemia intermedia based on clinical and hematological characteristics. Beta-globin mutations were studied using a reverse-hybridization assay and sequencing of the total beta-globin gene. The XmnI (G)gamma polymorphism, the Sicilian delta beta deletion, and four alpha-globin mutations (-a(3.7), -a(4.2), -(MED), aaa(anti-3.7)) were studied using PCR-based techniques. The inheritance of the XmnI (G)gamma polymorphism with severe beta-thalassemia alleles in the homozygous or compound heterozygous state was the predominant mechanism observed in 27 individuals (55.3%). In five cases, this status overlapped with the -a(3.7)/aa genotype. The second most frequent cause for thalassemia intermedia (14.8%) was the inheritance of mild beta-thalassemia alleles, including IVS-I-6 (T > C), -88 (C > A), and + 113 (A > G). In three subjects (4.3%) the Sicilian delta beta deletion was identified. HbS in association with beta-zero-thalassemia was found in three patients with thalassemia intermedia phenotype. In 11 cases (21.3%) no causative genetic alteration could be identified. Our results reflect the diversity underlying thalassemia intermedia, and the limitations of the applied clinical, hematological, and molecular approaches for correct diagnosis. Some of the unresolved cases will offer an opportunity to discover additional molecular mechanisms leading to thalassemia intermedia.

Molecular basis of thalassemia in Qatar

There is a paucity of information on the molecular basis of beta-thalassemia (thal) in Qatar, a country in the southern part of the Arabian Gulf. To decipher the molecular spectrum of beta- thalassemic alleles present in Qatar, we studied 31 clinically recognized patients, including three with sickle cell disease and beta-thal, and an additional six cases referred for unexplained microcytic anemia. We found 12 different beta-thalassemic alleles and two yet to be defined alleles, mutations likely occurring elsewhere than in the beta-globin gene per se. This is quite striking, given the small size of the study population, and highlights not only the ethnic diversity, but also the necessity of further investigating the thalassemic spectrum.