Characterization of two unique α-globin gene cluster deletions causing α-thalassemia in Israeli Arabs

Characterisation of two unusual cases of haemoglobin Bart's hydrops foetalis caused by -SEA and large novel α-globin gene cluster deletions

Background

We describe 2 unusual haemoglobin (Hb) Bart’s hydrops cases that could not be explained by traditional factors.

Case presentation: Two families with a diagnosis or history of foetal hydrops were enrolled. A suspension-array system was used to detect the 23 most frequent mutations in southern China. Multiplex ligation-dependent probe amplification (MLPA) was used to screen for possible deletions. Precise characterisation of the breakpoints of the novel variants and uniparental disomy analysis were performed using a single nucleotide polymorphism (SNP) array. Quantitative fluorescence PCR was used to eliminate maternal cell contamination and nonpaternity. In case 1, the suspension-array system indicated a maternal heterozygous (–^SEA/) deletion, and the paternal sample was negative. The foetal hydrops was caused by the maternal (–^SEA/) deletion and a de novo α-globin gene deletion (–¹⁹³). In case 2, the paternal sample had a heterozygous (–^SEA/) deletion, and MLPA and SNP array analysis revealed a large maternal deletion (–²²⁷) that encompassed the α-globin gene, which explained the history of Hb Bart’s foetal hydrops.

Conclusions

Our cases describe 2 new α⁰-thalassaemia deletions and illustrate the importance of using a combination of methods to detect rare types of α-thalassaemia.

Co-inheritance of alpha globin gene deletion lowering serum iron level in female beta thalassemia patients

In the Eastern province of Saudi Arabia, thalassemia is highly common. Data on the effect of alpha globin gene variation on the concentration of iron on transfusion dependent Saudis are scanty. A total of 166 transfusions dependent β-thalassemia were included in this study to understand association between the alpha globin gene variation and concentration of iron. Using multiplex PCR, the alpha globin gene deletions were identified. Also, HBA1 and HBA2 genes were sequenced by Sanger sequencing. Saudi transfusion dependent female β-thalassemia patients with wild alpha globin genotype (αα/αα) were observed with iron level beyond the normal range. However, normal range of iron was observed in transfusion dependent Saudi female beta thalassemia patients co-inherited with double (-α^3.7/-α^3.7, or --^Fil/αα or --^MED/αα or - (α) ^20.5/αα) or double heterozygosity (- -/-α^3.7) alpha globin gene deletions, which is significantly (p < 0.0001) less compared to the Saudi transfused female with wild alpha globin genotype (αα/αα). The co-inheritance alpha globin gene deletions in female beta thalassemia patients were significantly lowering serum iron. Detailed studies can be taken forward to identify the molecular pathways involved in globin gene deletion as modulator.

Characterization of a Large Novel α-Globin Gene Cluster Deletion Causing α0-Thalassemia in a Chinese Family

We report a large novel α-globin cluster deletion that we named - -^PG (NG_000006.1: g.93628_542759del450131), in a Chinese family. This large deletion is approximately 450 kb long, spanning from upstream of the PolR3k gene at the 5' end to the RAB11FIP3 gene at the 3' end of chromosome 16p13.3. This deletion removes all the globin distal regulatory elements as well as the whole α-globin gene cluster. Patients with heterozygous - -^PG/αα had red blood cell (RBC) indices consistent with α-thalassemia (α-thal) trait, but no apparent increase in a cancer tendency or mental disability, microcephaly, relative hypertelorism, unusual facies or genital anomalies.

The ‑α3.7 deletion in α‑globin genes increases the concentration of fetal hemoglobin and hemoglobin A2 in a Saudi Arabian population

The regions of Al‑Qatif and Al‑Ahssa in the Eastern Province of Saudi Arabia are known for their high prevalence of hemoglobinopathies, including β‑thalassemia and sickle cell anemia. Previously, the α‑gene deletion has been demonstrated as highly prevalent among populations residing in these two regions. The present study was conducted in order to investigate the implications of the α‑globin gene deletion on fetal hemoglobin (HbF) and hemoglobin α2 (HbA2) concentrations in patients with transfusion‑dependent β‑thalassemia. A total of 166 Saudi patients with transfusion‑dependent β‑thalassemia and 337 healthy Saudi patients were included in the study. The ‑α3.7, ‑α4.2, -‑FIL, -‑SEA, -‑MED and -‑(20.5) gene deletions were identified using multiplex α‑globin deletion polymerase chain reaction. The present study revealed that the ‑α3.7 gene deletion is the most prevalent (43.5%) in the Saudi populations that were analyzed and is characterized by the deletion of 3,804 base pairs. Numerous genotypes, namely ‑3.7α2/α1α2, ‑3.7α2/α1α12, ‑3.7α2/‑3.7α2, ‑3.7α2HphI/α1α2HphI, ‑3.7α2/α1‑4.2, ‑3.7α2/α1polyA‑1α2, ‑3.7α12/α1α12, ‑‑FIL/‑3.7α2 and ‑3.7α2/‑3.7α2Hb Villiers le Bel were also identified in the investigated population. Furthermore, a gradual increase in the concentration of HbF and HbA2 in patients with β‑thalassemia and the number of α‑gene deletions was demonstrated; whereas in healthy patients the level of HbA2 was demonstrated to decrease as the number of α‑gene deletions increased. Therefore, it can be concluded that the high HbF concentration in the present study is predominantly associated with other mutations associated with β‑thalassemia rather than α‑globin deletions. Furthermore, the results of the present study also revealed novel α‑gene deletion genotypes prevalent in the population studied, namely α1α2/α1α2HphI, α1α2HphI/α1α2HphI, α1α2/α1α2Hb Handsworth, ‑3.7α2HphI/α1α2HphI, ‑3.7α2/‑3.7α2Hb Villiers le Bel and ‑-MED/α1α2HphI.

Rare α0-thalassemia deletions detected by MLPA in five unrelated Brazilian patients

Alpha-thalassemias are among the most common genetic diseases in the world. They are characterized by hypochromic and microcytic anemia and great clinical variability, ranging from a practically asymptomatic phenotype to severe anemia, which can lead to intrauterine or early neonatal death. Deletions affecting the α-globin genes, located on chromosome 16p13.3, are the main causes of α-thalassemia. Multiplex ligation-dependent probe amplification (MLPA) can be used to detect rearrangements that cause α-thalassemia, particularly large deletions involving the whole α cluster and/or deletions in the HS-40 region. Here, MLPA was used to investigate the molecular basis of α-thalassemia in five unrelated patients, three of whom had Hb H disease. In addition to the -α3.7 deletion identified in the patients with Hb H disease, four different α0 deletions removing 15 to 225 kb DNA segments were found: two of them remove both the α genes, one affects only the regulatory element (HS-40) region, and another one extends over the entire α cluster and the HS-40 region. These results illustrate the diversity of α-thalassemia deletions in the Brazilian population and highlight the importance of molecular investigation in cases that present with microcytosis and hypochromia without iron deficiency and normal or reduced Hb A2 levels..

Novel 31.2 kb α0 Deletion in a Palestinian Family with α-Thalassemia

A previously unknown α(0) deletion, designated - -(DANE), was found in three generations of a Danish family of Palestinian origin. Six patients were heterozygous and three patients had deletional Hb H (β4) disease with a compound heterozygosity for the common -α(3.7) (rightward) deletion. Multiplex ligation-dependent probe amplification (MLPA) supplemented by repeated polymerase chain reaction (PCR) amplification identified the 5' and 3' breakpoints in the α-globin gene cluster. This novel 31.2 kb deletion (NG_000006.1: g.8800_40007del31208) leads to the removal of the HBZ, HBA2 and HBA1 genes.