A stepwise α-thalassemia screening strategy in high-prevalence areas

Profiling of 35 Cases of Hb S/Hb E (HBB: c.20A>T/HBB: c.79G>a), Disease and Association with α-Thalassemia and β-Globin Gene Cluster Haplotypes from Odisha, India

Hb S/Hb E (HBB: c.20A>T/HBB: c.79G>A) is an uncommon variant of sickle cell disease resulting from coinheritance of Hb S and Hb E. Clinico-hematological and biochemical parameters of 35 cases of Hb S/Hb E disease were studied and compared with 70 matched cases of homozygous sickle cell disease (Hb SS) and Hb S/β-thalassemia (β-thal) with IVS-I-5 (G>C) (HBB: c.92+5G>C). The influence of α-thal and that of of β-globin gene cluster haplotypes among Hb S/Hb E disease was also studied. Statistical analysis was done using GraphPad InStat version 3.06. Of the 35 cases, 20 (57.14%) had a moderate clinical presentation. Mean lactate dehydrogenase (LDH) level, vaso-occlusive crises (VOCs) per year, and annual blood transfusion requirements were significantly lower in Hb S/Hb E cases than in the other two groups. The hemoglobin (Hb) and packed cell volume (PCV) levels were significantly high in Hb S/Hb E cases with α-thal and these cases were associated with microcytic-hypochromic anemia. α-Thalassemia did not influence clinical presentation in Hb S/Hb E cases. The β-globin gene cluster haplotypes of 70 alleles of Hb S/Hb E revealed an association of five typical haplotypes [Arab-Indian (A-I), Benin, Bantu, Cameroon and Senegal] in 95.71% cases. Hb S/Hb E disease exhibit asymptomatic to moderate phenotypic expression. However, further in-depth studies on Hb S/Hb E will help in reducing the disease burden especially in high-risk countries like India.

α-Globin Genotypes Associated with Hb H Disease: A Report from Oman and a Review of the Literature from the Eastern Mediterranean Region

α-Thalassemia (α-thal) is the most common autosomal recessive hemoglobinopathy. There is a vast diversity and geographical variability in underlying genotypes in Hb H (β4) patients. Herein, we describe the genotypes found in the largest report of Omani Hb H patients. Moreover, we reviewed and summarized the literature published from the Eastern Mediterranean region. A retrospective review of all genetically confirmed Hb H disease patients diagnosed between 2007 and 2017 at Sultan Qaboos University Hospital, Muscat, Oman, was performed. Hematological parameters and clinical presentations were assessed. Both α-globin genes were screened for deletional and nondeletional mutations using a stepwise diagnostic strategy as described before. A total of 52 patients (27 females and 25 males) with a mean age of 20.6 years (range 0.23-80.0) were molecularly confirmed to carry Hb H disease. The patients had a hemoglobin (Hb) level of 9.3 g/dL (range 5.7-13.0) and mean corpuscular volume (MCV) of 58.4 fL (range 48.2-82.1). A total of eight genotype combinations were identified, with α2 polyadenylation signal mutation (polyA1) (AATAAA>AATAAG (α^PA1α/α^PA1α), often cited as α^T-Saudiα/α^T-Saudiα, being the most common (53.8%) followed by -α^3.7/- -^{MED I} (28.8%). Our cohort also included patients with combinations of α^PA1 with other Hb variants: α^PA1α/α^PA1α with Hb S (HBB: c.20A>T) trait (n = 2), -α^3.7/α^PA1α (n = 2) and α^{codon 19}α (HBA2: c.56delG)/α^PA1α (n = 1). Nondeletional Hb H disease due to the α^PA1 mutation is the most common in Omanis. Molecular diagnosis is necessary for accurate confirmation of the diagnosis of α-thal, determination of underlying genotypes, follow-up and counseling.

C>A substitution in NT 46 of the 3' UTR region (the α complex protected region) of the alpha-1 globin gene: a non-deletional mutation or polymorphism?

AIMS

Untranslated regions (UTRs) play an important role in post-transcriptional regulation of gene expression, including by modulating messenger RNA (mRNA) transport out of the nucleus, translation efficiency, subcellular localisation and stability. Any mutation in this region could alter the stability of mRNA and thereby affect protein synthesis. We analysed if a mutation located in the α complex protected region of the α1 globin gene could cause non-deletional α-thalassaemia by affecting post-transcriptional stability (mRNA stability).

METHODS

A total of 14 patients without anaemia, normal or slight microcytosis and hypochromia (medium concentration haemoglobin [MCH] <27 pg) were studied. Haemoglobin subtypes were screened using capillary zone electrophoresis and ion-exchange high-performance liquid chromatography (VARIANT II β-Thalassaemia Short Program). The most common α-globin mutations were identified by multiplex PCR (Alpha-Globin StripAssay kit) and the molecular characterisation by automatic sequencing of alpha globin genes.

RESULTS

All of them shown a novel transversion mutation in nt 778 (C>A), which is located in the 3' UTR in the α complex protected region [HBA1: c.*+46C>A].

CONCLUSIONS

This mutation is in the αRNAmin binding site, so a single nucleotide substitution in this region can decrease mRNA stability by potentially compromising the binding of α-complex protein to αRNAmin, favouring the decay of α-globin mRNA via erythroid cell-enriched endoribonuclease cleavage. In this case, it is a non-deletional α-thalassaemia. However, in silico and empirical studies predicted that it could be a silent polymorphism. Functional studies should be carried out to confirm whether it is a pathological mutation or a silent polymorphism.

The Use of HPLC as a Tool for Neonatal Cord Blood Screening of haemoglobinopathy: A Validation Study

Background

Newborn cord blood screening identifies infants with underlying haemoglobinopathies before they develop the characteristic symptoms or sequelae.

Aims

This study was performed to validate the interpretation high-performance chromatography (HPLC) along with complete blood count (CBC) results as a tool for universal neonatal screening of hemoglobin disorders in Oman.

Methods

HPLC and CBC data on subjects who participated in the National Neonatal screening program at birth were obtained from archival records. The results recorded at birth were compared with a second study performed on the same subjects, after approval from the local medical research and ethics committee.

Results

Only 290 subjects from amongst the original cohort of 3740 newborns could be recalled between April 2010 to March 2011, to repeat HPLC and CBC, as well as perform confirmatory DNA studies, wherever necessary. All these subjects had been documented to show an initial abnormal result. 31 cases who had no HbA at birth on HPLC were confirmed as either homozygous β-thalassaemia major (n=5 subjects) or homozygous sickle cell anemia (n=26 subjects) by appropriate DNA analysis. Additionally, amongst 151 subjects, 72 subjects were studied in the initial study by Hb Bart’s quantitation using the alpha thalassaemia short program at birth. In this cohort, 42 subjects with Hb Bart’s >1% at birth could be confirmed as having either deletional or non-deletional thalassaemia by GAP PCR studies. No case of HbH was detected in this cohort. Further, carrier status for structural hemoglobin variants (HbS, HbC, HbD, HbE) (n=67) and beta thalassaemia allele with low HbA at birth (n=29 out of 41) were confirmed by relevant molecular studies.

Conclusions

The study validated the earlier observation by 100% concordance with the results of CBC and HPLC. Presence of Hb Bart’s at birth does not always mean the presence of alpha thalassemia, as subjects with Hb Bart’s below 1% by quantitation, were shown to be normal by molecular studies.

Haemoglobin Fontainebleau (HBA2: c. 64G>C) in Oman: molecular and haematological characteristics and interaction with various haemoglobinopathies

Objectives

To describe the laboratory features of haemoglobin Fontainebleau (Hb FB) and its interactions with various α and β globin gene mutations in the Omani population.

Methods

Over a period of 10 years, a total of 94 blood samples were suspected to have an α variant on HPLC at the Sultan Qaboos University Hospital, Muscat, Oman. Molecular testing was performed using PCR based techniques to define the variant and to analyse other interacting mutations in either α or β globin genes.

Results

Of 94 subjects, molecular analysis confirmed the Hb FB variant in 55 samples (38 non-cord and 17 cord blood). A total of 36/38 non-cord samples were heterozygous for the variant, while all 17 cord blood samples were heterozygotes. A total of 43/55 individuals had a concomitant α and/or β globin gene mutation.

Conclusions

Hb FB is the the most common α variant in the Omani population. We report the different HPLC profiles of this variant that we observed, with and without other haemoglobinopathies in non-cord and cord blood samples. This is the first report describing the HPLC profiles of this α globin chain variant on 1 year follow-up testing of cord blood samples. With careful analysis by HPLC, it is possible not only to identify Hb FB but also to predict any concomitant α and/or β globin gene mutations.

Development and validation of a high throughput, closed tube method for the determination of haemoglobin alpha gene (HBA1 and HBA2) numbers by gene ratio assay copy enumeration-PCR (GRACE-PCR)

BACKGROUND

Deletions of the α-globin genes are the most common genetic abnormalities in the world. Currently multiplex Gap-PCRs are frequently used to identify specific sets of common deletions. However, these assays require significant post-amplification hands on time and cannot be used to identify novel or unexpected deletions. The aim of the current study was to develop a rapid screening test for the detection of all deletions of the α-globin genes that can be integrated into a high volume clinical laboratory workflow.

METHODS

A gene ratio assay copy enumeration (GRACE) PCR method was developed by simultaneous amplification of targets in the α-globin genes (HBA1 and HBA2) and the chloride channel voltage sensitive 7 (CLCN7) reference gene. A novel application of High Resolution Melting (HRM) analysis then allowed rapid determination of α-globin gene copy numbers. The assay was validated using 105 samples with previously determined and 62 samples with unknown α-globin genotypes.

RESULTS

The GRACE-PCR assay detected abnormal α-globin gene copy numbers in 108 of the 167 samples evaluated. The results were consistent with those from a commercial reverse hybridization assay and no allele drop out was observed.

CONCLUSIONS

We have successfully developed and validated a GRACE-PCR screening test for the detection of deletions and duplications of the α-globin genes. The assay is based on copy number determination and has the ability to detect both known and novel deletions of the α-globin genes. It is a closed tube technique; consequently the risk of amplicon contamination is negligible. Amplification, detection and analysis can be completed within one hour, making it faster, cheaper and simpler than other existing tests and thus well suited as a rapid first step in a clinical laboratory workflow.

Serum Total Bilirubin, not Cholelithiasis, is Influenced by UGT1A1 Polymorphism, Alpha Thalassemia and β(s) Haplotype: First Report on Comparison between Arab-Indian and African β(s) Genes

Background

We explored the potential relationship between steady state serum bilirubin levels and the incidence of cholelithiasis in the context of UGT1A1 gene A(TA)nTAA promoter polymorphism in Omani sickle cell anemia (SCA) patients, homozygotes for African (Benin and Bantu) and Arab-Indian β^S haplotypes, but sharing the same microgeographical environment and comparable life style factors.

Methods

136 SCA patients were retrospectively studied in whom imaging data including abdominal CT scan, MRI or Ultrasonography were routinely available. Available data on the mean steady state hematological/biochemical parameters (n=136), β^s haplotypes(n=136), α globin gene status (n=105) and UGT1A1 genotypes (n=133) were reviewed from the respective medical records.

Results

The mean serum total bilirubin level was significantly higher in the homozygous UGT1A1(AT)₇ group as compared to UGT1A1(AT)₆ group. Thus, not cholelithiasis but total serum bilirubin was influenced by UGT1A1 polymorphism in this SCA cohort.

Conclusion

As observed in other population groups, the UGT1A1 (AT)₇ homozygosity was significantly associated with raised serum total bilirubin level, but the prevalence of gallstones in the Omani SCA patients was not associated with α thalassaemia, UGT1A1 polymorphism, or β^s haplotypes.

[Clinical consequences of alpha-thalassemia in the Basque Country, Spain. Impact of neonatal screening]

INTRODUCTION

Alpha-thalassemia is the most common hemoglobinopathy with a variable clinical manifestation depending on the number of allele mutations (asymptomatic/mild anemia if 1-2 allele mutations, severe disease if 3-4 allele mutations). A study was conducted from May 2011 on hemoglobinopathies found in the neonatal screening in the autonomous community of the Basque Country (CAPV).

OBJECTIVES

To analyze the impact of alpha-thalassemia in this area and the effectiveness of its neonatal screening.

METHODS

A review was made of patients with a positive gene study for alpha-thalassemia over a 2-year period (2012-2013) and an analysis was made of the age at diagnosis, ethnic group, analytical result, and treatment.

RESULTS

The genetic study was performed on 107 patients, of which 61 had some mutation, with 62% having one allele mutations and 38% with two alleles. The mean age at diagnosis was 31 years, with 28% being younger than eighteen years old. Most of the patients were European with a significant number of Africans (26%) and Arabs (13%). All patients were asymptomatic, and 28% had mild anemia. Two patients were diagnosed by neonatal screening. Most of them did not need any treatment or only required iron therapy.

CONCLUSIONS

The detection of one or two alpha gene mutations has no clinical impact, but allows genetic counseling. No patient was found with 3-4 mutations or severe symptoms in our region. Contrarily to the diagnosis of other diseases, our results does not support that routine neonatal screening for alpha-thalassemia has any clinical impact in our community.

Molecular spectrum of α-globin gene defects in the Omani population

We describe the molecular characterization of α-globin gene defects in a cohort of 634 Omani patients. A total of 21 different α gene mutations were found in 484 subjects. Overall, we identified three different large deletions, three small deletions, 11 point mutations [two on the α2 polyadenylation signal (polyA) (HBA2: c.*94A>G), and nine α chain variants], three ααα(anti 3.7) triplication, a 21 nucleotide (nt) duplication on the α1 gene and two novel (presumed) polymorphisms on the α 3.7 kb hybrid gene, namely -5 (C>T) and +46 (C>A). Of these defects, 15 have not been previously reported in the Omani population. This large heterogeneity of α-thalassemia (α-thal) observed in the Omani population could be expected in neighboring Arab countries. The high frequency of α-thal, solely or in association with β-globin gene defects, emphasize the necessity of adding α-thal testing to pre marital programs for accurate genetic counseling.

Fetal hemoglobin and alpha thalassemia modulate the phenotypic expression of HbSD-Punjab

INTRODUCTION

HbSD-Punjab (HbSD) is a less common form of sickle cell disease (SCD) and discrimination between HbSD and HbSS is not possible on alkaline electrophoresis because the two variants overlap in the compound heterozygous state. There are only a few publications consisting mostly of case reports. Thus, the phenotypic expression of HbSD and its modifiers has not been studied.

METHODS

We studied the phenotypic expression of 42 cases of HbSD (the largest number of subjects ever included in this kind of study) and compared them with 84 HbSS cases matched for age, sex, and caste. Further, we evaluated the influence of HbF concentration and alpha thalassemia on the phenotypic expressions of HbSD, namely the frequency of VOC and degree of hemolysis.

RESULTS

The frequencies of VOC were similar in both the groups. The markers of hemolysis such as total bilirubin, unconjugated bilirubin, and LDH were higher where as HbF concentration was significantly low in HbSD. There was a negative correlation between HbF concentration and risk of VOC in the HbSD. The total hemoglobin level and hematocrit were significantly high, and the MCV and MCH were significantly low in HbSD with alpha thalassemia. Alpha thalassemia had no influence on the frequency of VOC and severity of hemolysis in HbSD.

CONCLUSION

HbF reduced the frequency of VOC but had no influence on the hemolytic markers in HbSD. HbSD with alpha thalassemia was associated with hypohromic and microcytic features of red blood cells.

Potential pitfalls in the diagnosis of Hb Handsworth in areas with high prevalence of HbS

Hb Handsworth is a rare α-globin structural variant caused by a missense mutation either on the α2 or α1-globin gene (HBA2 or HBA1: c.55G>C, p.Gly18Arg). This variant might be erroneously diagnosed as HbS unless secondary confirmative tests are carried out. We encountered a child with a prominent peak eluting in the 'S' window on high-performance liquid chromatography (HPLC). Sickle solubility test, gel electrophoresis, and selective direct nucleotide sequencing of α1, α2, and β globin genes were performed on the patient's sample. In addition, previous HPLC results on a cord blood sample were retrieved. Sickle solubility test was negative. Gel electrophoresis revealed a band migrating at the S region with an extra faint band seen on acid gel electrophoresis. Molecular analysis of α2 globin gene revealed heterozygous state of Hb Handsworth. Hb Handsworth is a rare variant that can mimic HbS on HPLC. Failure to recognize this rare variant in regions where HbS is highly prevalent may result in serious misdiagnosis and subsequent incorrect genetic counseling.