Thalassaemia genes in Peninsular Arabs

β-Thalassemia and Diabetes Mellitus: Current State and Future Directions

β-Thalassemia major is a congenital hemoglobin disorder that requires regular blood transfusion. The disease is often associated with iron overload and diabetes mellitus, among other complications. Pancreatic iron overload in β-thalassemia patients disrupts β-cell function and insulin secretion and induces insulin resistance. Several risk factors, including family history of diabetes, sedentary lifestyle, obesity, gender, and advanced age increase the risk of diabetes in β-thalassemia patients. Precautionary measures such as blood glucose monitoring, anti-diabetic medications, and healthy living in β-thalassemia patients notwithstanding, the prevalence of diabetes in β-thalassemia patients continues to rise. This review aims to address the relationship between β-thalassemia and diabetes in an attempt to understand how the pathology and management of β-thalassemia precipitate diabetes mellitus. The possible employment of surrogate biomarkers for early prediction and intervention is discussed. More work is still needed to better understand the molecular mechanism(s) underlying the link between β-thalassemia and diabetes and to identify novel prognostic and therapeutic targets.

Alpha thalassemia genotypes in Kuwait

Background

The frequency of the alpha thalassemia trait is approximately 40% in the Kuwaiti population, but there has been no comprehensive study of the prevalent alleles. This is a report of patients who were referred for molecular diagnosis over a 20-year period.

Methods

This is a retrospective study of the α-globin genotypes obtained in the Hemoglobin Research Laboratory of the Department of Pediatrics, Kuwait University from 1994 to 2015. Genotyping was performed by a combination of PCR, allele-specific oligonucleotide hybridization and reverse dot blot hybridization (Vienna Lab Strip Assay).

Results

Four hundred samples were characterized and analyzed from individuals aged < 1 month to 80 years, with a median of 6 years from 283 unrelated families. Most (90.8%) were Kuwaiti nationals. The commonest genotype was homozygosity for the polyadenylation-1 mutation (α^PA-1α/α ^PA-1α) in 33.3% of the samples, followed by heterozygosity (αα/α ^PA-1α) for the same mutation in 32.3%. PA-1 was therefore the most frequent allele (0.59). The frequency of the α⁰ (−-^MED) allele was 0.017. Rare alleles that were found in very low frequencies included α⁰ (−-^FIL) in a Filipino child, Hb Constant Spring, Hb Adana, and Hb Icaria.

Conclusion

There is a wide variety of alpha thalassemia alleles among Kuwaitis, but nondeletional PA-1 is by far the most common cause of the moderate to severe HbH (β4 tetramer) disease phenotype. The α⁰ (−^MED) allele is also encountered, which has implications for premarital counseling, especially for the possibility of having babies with alpha thalassemia major (Barts hydrops fetalis).

The super sickling haemoglobin HbS-Oman: a study of red cell sickling, K+ permeability and associations with disease severity in patients heterozygous for HbA and HbS-Oman (HbA/S-Oman genotype)

Studying different sickle cell genotypes may throw light on the pathogenesis of sickle cell disease (SCD). Here, the clinical profile, red cell sickling and K⁺ permeability in 29 SCD patients (15 patients with severe disease and 14 with a milder form) of HbA/S-Oman genotype were analysed. The super sickling nature of this Hb variant was confirmed. The red cell membrane permeability to K⁺ was markedly abnormal with elevated activities of P_sickle , Gardos channel and KCl cotransporter (KCC). Results were consistent with Ca²⁺ entry and Mg²⁺ loss via P_sickle stimulating Gardos channel and KCC activities. The abnormal red cell behaviour was similar to that in the commonest genotype of SCD, HbSS, in which the level of mutated Hb is considerably higher. Although activities of all three K⁺ transporters also correlated with the level of HbS-Oman, there was no association between transport phenotype and disease severity. The super sickling behaviour of HbS-Oman may obviate the need for solute loss and red cell dehydration to encourage Hb polymerisation, required in other SCD genotypes. Disease severity was reduced by concurrent α thalassaemia, as observed in other SCD genotypes, and represents an obvious genetic marker for prognostic tests of severity in young SCD patients of the HbA/S-Oman genotype.

Molecular basis of β-thalassemia in the United Arab Emirates

In an attempt to define the prevalence of β-thalassemia (β-thal) in the United Arab Emirates (UAE), we have conducted molecular studies on nearly 2000 randomly-selected adult UAE nationals. The results demonstrated that the prevalence of β-globin gene defects in the UAE was 8.5%. Among these anomalies were β-thal mutations, abnormal hemoglobin (Hb) variants, e.g., Hb S, Hb D-Punjab, Hb O-Arab, Hb C and Hb E. The sickle gene (β(S) or Hb S) contributed significantly to the molecular epidemiology of the hemoglobinopathies in the UAE. In this article, Hb S and other abnormal Hbs are excluded as they are comprehensively described by other contributors in this current issue. The molecular characterization and mutational analyses of all β-thal patients were carried out using current molecular techniques including amplification refractory mutation system (ARMS), restriction enzyme analysis (REA), dot-blot hybridization, β-strip hybridization, allele-specific oligonucleotide (ASO), polymerase chain reaction (PCR), gap-PCR and DNA Sequencing. Most of these techniques are now virtually obsolete. Almost all molecular characterizations are currently performed through PCR followed by DNA sequencing using a fully automated ABI PRISM™ 3130 Genetic Analyzer. Our molecular studies showed that the majority of the β-thal mutations in the UAE are very severe; the most common allele was the IVS-I-5 (G>C). Although this allele is a β(+)-thal, its phenotype is very severe. All other mutations are also severe β(0)-thal. High frequency of moderate or severe β-thal mutations have implications in the wide spectrum of clinical manifestations seen in patients whose phenotypes vary from β-thal intermedia (β-TI) to severe transfusion-dependent β-thal major (β-TM). The molecular pathology of the β-thal patients demonstrated that a vast majority were homozygous. The most frequent homozygous mutation was the IVS-I-5(G>C)/IVS-I-5(G>C) (53.0%) followed by -25 bp del/-25 bp del (6.8%), codons 8/9(+G)/codons 8/9(+G) (2.8%) and codon 39(C>T)/codon 39(C>T) (2.4%). Four mutations accounted for 65.0% of the homozygous patient population. Remarkably, the two most prevalent mutations, IVS-I-5 and Hb S, accounted for 77% of all the homozygous β-thal patients from the UAE. We showed 13 discrete homozygosities in the UAE national patients in contrast to 23 homozygosities in the expatriate population. Since the number of homozygous mutations has a direct correlation with the degree of consanguinity, the data shown here corroborate the social tendency towards family planning. In fact, in the UAE, more than 50% of all marriages are between relatives and more than half of these are between first cousins.

Pregnancy outcome data in a United Arab Emirates population: what can they tell us?

A cross-sectional study of pregnancy outcome in a national Arabic population is presented to highlight a unique reproductive environment compared with many other obstetric populations. A high pro-natal intensity is evident with significant numbers of grandmultipara (36.7%) and mature gravida (22.2%). These groups did not show any significant increase in adverse antenatal or intrapartum events apart from an increasing rate of gestational diabetes with maternal age. There was an average induction/augmentation rate of 10.2% with a low rate of instrumental delivery (2.3%) and a mean caesarean section rate of 6.9%. A major antenatal complication noted was the prevalance of 17.3% for a haemoglobin < 10 g/dl together with overall increased rates of pre-existing and gestational diabetes. In addition the incidence of preterm labour increased over each of the 3 years studied and is of concern.

Grandmultiparity--not to be feared? An analysis of grandmultiparous women receiving modern antenatal care

OBJECTIVE

To document the reproductive performance of grandmultiparous women receiving modern antenatal care.

METHODS

A cross-sectional study of 2784 multiparous (882 grandmultiparous) mothers delivered in a base hospital obstetric unit staffed by western-trained midwives and consultant obstetrical staff.

RESULTS

There were minimal differences in major antenatal, peripartum and neonatal outcome events, with the exception of a high rate of gestational and pre-existing diabetes.

CONCLUSIONS

This data supports the opinion that grandmultiparity per se is not necessarily a major risk factor for either mother or fetus. Similarly, the mature grandmultigravida in this population was not at significantly increased risk of the alleged associations of increased parity and advancing maternal age, with the exception of diabetes. Together with the combined prevalence of maternal anemia this requires further investigation and probable intervention, particularly in the light of recent speculation concerning the fetal and infant origins of adult disease.

Red cell genetic abnormalities in Peninsular Arabs: sickle haemoglobin, G6PD deficiency, and alpha and beta thalassaemia

The frequencies of four major red cell genetic defects, sickle haemoglobin (Hb S), glucose 6 phosphate dehydrogenase deficiency (G6PD), and alpha and beta thalassaemia, have been determined in nearly 5000 subjects from the three major Peninsular Arab States, namely Yemen (North and South), the United Arab Emirates, and Oman. All four defects are common with an overall pattern of alpha thalassaemia greater than G6PD deficiency greater than beta thalassaemia greater than Hb A/S. However, the frequencies of these within each state varies and they are, respectively, Oman: 0.389, 0.328, 0.024, and 0.038; the United Arab Emirates: 0.165, 0.087, 0.017, and 0.019; and Yemen: 0.065, 0.062, 0.0624, and 0.0095. Two, namely alpha thalassaemia and G6PD deficiency, are extremely common, but in spite of this there appears to be a lack of observed clinical disease. For example, Hb H disease and Barts hydrops fetalis were not seen and the oxidative haemolytic syndromes are rare.