Genotype-phenotype Correlation of β-Thalassemia in Croatian Patients: A Specific HBB Gene Mutations

The Relevance of β-Thalassemia Heterozygosity in Pediatric Clinical Practice: Croatian Experience

(1) Background: Thalassemia syndromes are common monogenic disorders that represent a significant global health issue. No systematic epidemiological or molecular investigations on thalassemias in the Croatian population have been reported to date. (2) Methods: This prospective study included 70 children with a presumptive diagnosis of thalassemia and their 42 first-degree relatives. Molecular characterization was performed using direct sequencing and gap-PCR methods. (3) Results: We identified 46 (30 children and 16 first-degree relatives) β-thalassemia heterozygous carriers from 24 unrelated families, carrying eight different mutations and one hemoglobin variant. Five variants account for approximately 85% of all affected β-globin alleles: Hb Lepore-Boston-Washington (32.6%), HBB:c.93-21G>A (19.6%), HBB:c.315+1G>A (13.1%), HBB:c.92+1G>A (10.9%), and HBB:c.92+6T>C (8.7%) variants. (4) Conclusions: β-thalassemia carriers need more detailed genetic profiling since genetic modifiers can significantly impact their phenotype. Our study provides important new insights into the relevance of β-thalassemia heterozygosity in pediatric clinical practice.

Direct sequencing of β-globin gene reveals a rare combination of two exonic and two intronic variants in a β-thalassemia major patient: a case report

Background

Due to indels in the β-globin gene, patients with β-thalassemia major exhibit a range of severity, with genotype β⁰β⁰ > β⁰β⁺ > β⁺β⁺, according to the production level of the β-globin chain. More than 300 mutations have been identified in the β-globin gene.

Case presentation

In this case study, we report a compound heterozygous condition with a rare concoction of four different variants (CD 3(T > C), CD41/42 (-CTTT), IVS II-16 (G > C), and IVS II-666 (C > T) in a single β-globin gene. A regular transfusion-dependent 4-year-old male patient from India was included in the study. Augmented direct sequencing of the β-globin gene helped reveal the presence of an unusual combination of different variants in a single gene. This patient clinically presented as β-thalassemia major and was genotypically considered as β⁰β⁺, although CD41/42(-CTTT) was the only causative/pathogenic mutation in the disease severity.

Conclusion

Although CD41/42-(CTTT) is the only pathogenic variant among the four variants, the clinical complications of such a combination of variants (pathogenic and benign) is not well understood. Intronic mutations may have the ability to modify clinical characteristics. The variants must therefore be reclassified using additional mRNA splicing and expression-based studies. Additionally, these types of combinations may have significance in studying population migration around the world.

IVS-II-16 (G>C) (HBB: c.315+16G>C) or IVS-II-666 (C>T) (HBB: c.316-185C>T) Mutations Trigger an Hb S (HBB: c.20A>T)/β+-Thalassemia Phenotype in an Hb S Trait Patient

Sickle cell trait is a medical condition caused by the presence of both mutant Hb S (HBB: c.20A>T) and normal Hb A alleles. Although sickle cell trait is typically considered to be asymptomatic and benign, genetic modifiers and mutations can lead to severe clinical complications. In this study, the possible pathogenicity of the IVS-II-16 (G>C) (HBB: c.315+16G>C) and IVS-II-666 (C>T) (HBB: c.316-185C>T) mutations, which are considered to be neutral polymorphisms, and the association between the Hb S mutation are presented. To the best of our knowledge, these polymorphisms have not been previously reported in any sickle cell trait patient, and no relevant studies have been conducted. We recently studied a 40-year-old woman (proband), diagnosed to be an Hb S/β-thalassemia (β-thal) carrier. β-Globin mutations were analyzed using a DNA sequencer based on the Sanger method. The HbVar and ClinVar databases show IVS-II-16 and IVS-II-666 to be intronic mutations. However, statements in these data banks contradict our findings. In the present study, a transfusion-dependent Hb S patient, behaving as an Hb S/β-thal case due to these mutations, was reported. These mutations have not been previously reported in an Hb S patient. Although the IVS-II-16 and IVS-II-666 mutations were previously reported as benign, they converted the Hb S phenotype to transfusion-dependent Hb S/β-thal when combined with Hb S. In this regard, IVS-II-16 and IVS-II-666 mutations may not be innocent, as previously thought.

HBB mutations and HbA2 level: Escaping the carrier screening programs

HbA2 level alone for beta thalassemia trait may not be accurate and reliable even without iron deficiency so molecular genetic testing is important and should be considered for some individuals.

Distribution of HBB Gene Mutations in the Kurdish Population of Ilam Province, West Iran

β-Thalassemia (β-thal) is one of the most common diseases in Iran. Here, we report the spectrum of HBB gene mutations in 176 Kurdish β-thal carriers from the northern part of Ilam Province, Iran. The amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) technique was used to identify common β-globin gene mutations observed in Iran. Samples negative on ARMS-PCR were analyzed by direct sequencing of the β-globin gene. In total, 12 different mutations were identified on the β-globin gene. The mutations of IVS-II-1 (G>A) (HBB: c.315+1G>A), codons 8/9 (+G) (HBB: c.27_28insG), codons 36/37 (-T) (HBB: c.112delT) and IVS-I-110 (G>A) (HBB: c.93-21G>A), were the most prevalent mutations in our samples, with frequencies of 59.09, 10.80, 7.95 and 7.39%, respectively. In general, the mutation spectrum of the β-globin gene in the northern part of Ilam Province is most similar to that in other western provinces of Iran. On the other hand, due to the high prevalence of carriers and β-thal major (β-TM) patients in this province, our results can be helpful in identifying carriers as well as at-risk fetuses through the prenatal diagnosis program.

The Spectrum of β-Thalassemia Mutations in Hamadan Province, West Iran

β-Thalassemia (β-thal) is one of the most common hemoglobinopathies worldwide and is caused by mutations on the β-globin (HBB) gene. The aim of the present study was to determine the mutation spectrum of the β-globin gene in β-thal carriers who were originally from Hamadan Province, Western Iran. Two hundred and eighty-two β-thal carriers participated in the study. Amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) and direct sequencing were used for detection of different mutations. A total of 25 different mutations, including 21 β-thal mutations and four other hemoglobin (Hb) variants, in 280 β-thal carriers (99.3%) were detected in the present study. Three types of mutations including IVS-II-1 (G>A) (HBB: c.315+1G>A) (26.24%), codons 8/9 (+G) (HBB: c.27_28insG) (14.54%) and codons 36/37 (-T) (HBB: c.112delT) (12.76%) accounted for more than 50.0% of the identified mutations. Moreover, IVS-I-110 (G>A) (HBB: c.93-21G>A), codon 44 (-C) (HBB: c.135delC) and IVS-I (25 bp deletion) (HBB: c.93-21_del), had frequencies of 7.09, 7.09 and 5.67%, respectively. Allele frequencies of the remaining 19 mutations were less than 5.0%. This study is the first comprehensive study on a large sample size in Hamadan Province, Iran. In conclusion, the present study significantly increased the spectrum of HBB gene mutations in Hamadan Province compared with previous studies. Therefore, these results can be helpful in identifying β-thal carriers and at-risk fetuses through prenatal diagnosis (PND).