Molecular characterization of a novel 55.1 kb (G)gamma((A)gammadeltabeta)(0)-thalassemia deletion in two Canadian families

Identification of a rare [Gγ(Aγδβ)0] -thalassemia using tandem mass spectrometry

Thalassemias are a group of inherited monogenic disorders characterized by defects in the synthesis of one or more of the globin chain subunits of the hemoglobin tetramer. Delta-beta (δβ-) thalassemia has large deletions in the β globin gene cluster involving δ- and β-globin genes, leading to absent or reduced synthesis of both δ- and β-globin chains. Here, we used direct globin-chain analysis using tandem mass spectrometry for the diagnosis of δβ-thalassemia. Two cases from unrelated families were recruited for the study based on clinical and hematological evaluation. Peptides obtained after trypsin digestion of proteins extracted from red blood cell pellets from two affected individuals and their parents were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Mass spectrometric analysis revealed a severe reduction in δ, β, and Aγ globin proteins with increased Gγ globin protein in the affected individuals. The diagnosis of Gγ(Aγδβ)0 -thalassemia in the homozygous state in the affected individuals and in the heterozygous state in the parents was made from our results. The diagnosis was confirmed at the genetic level using multiplex ligation-dependent probe amplification (MLPA). Our findings demonstrate the utility of direct globin protein quantitation using LC-MS/MS to quantify individual globin proteins reflecting changes in globin production. This approach can be utilized for accurate and timely diagnosis of hemoglobinopathies, including rare variants, where existing diagnostic methods provide inconclusive results.

A large cohort of deletional high hemoglobin F determinants in Thailand: A molecular revisited and identification of a novel mutation

BACKGROUND AND AIMS

High hemoglobin F determinants can be classified into hereditary persistence of fetal hemoglobin (HPFH) and δβ-thalassemia with different phenotype. We report the molecular basis and hematological features in a large cohort of deletional high Hb F determinants in Thailand.

MATERIALS AND METHODS

Subjects (n = 28,177) encountered during 2015-2022 were reviewed, and those with phenotypically suspected of having high Hb F determinants were selected. Combined PCR, multiplex ligation-dependent probe amplification, next-generation sequencing, and DNA sequencing were used to identify the mutations.

RESULTS

Among 28,177 subjects investigated, 300 (1.06 %) were found to carry deletional high Hb F determinants in a total of 302 alleles, including heterozygote, compound heterozygote with β-hemoglobinopathies, and homozygote. DNA analysis identified eight different DNA deletions, including δβ0-thalassemia (12.6 kb deletion) (73.8 %), HPFH-6 (14.9 %), Indian deletion-inversion Aγδβ0-thalassemia (3.6 %), Thai deletion-inversion-insertion Aγδβ0-thalassemia (3.0 %), SEA-HPFH (3.0 %), Chinese Aγδβ0-thalassemia (1.0 %), Thai δβ0-thalassemia (11.3 kb deletion) (0.3 %), and a novel δβ0-thalassemia (137.1 kb deletion) (0.3 %). In addition, three novel genetic interactions, including Chinese Aγδβ0-thalassemia/Hb E, δβ0-thalassemia/Indian deletion-inversion Aγδβ0-thalassemia, and homozygous δβ0-thalassemia were found. Hematological features and Hb analysis results of 20 different genotypes were recorded. Multiplex gap-PCR assays for detection of these genetic determinants were described.

CONCLUSIONS

Deletional high Hb F determinants are common and heterogeneous in Thailand. Data on the prevalence, molecular spectrum, phenotypic expression, and complex interactions of these genetic determinants should prove useful in the study and a prevention and control program of hemoglobinopathies in the region.

Gap-PCR Screening for Common Large Deletional Mutations of β-Globin Gene Cluster Revealed a Higher Prevalence of the Turkish Inversion/Deletion (δβ)0 Mutation in Antalya

OBJECTIVE

Although the calculated carrier frequency for point mutations of the β-globin gene is around 10% for Antalya Province, nothing is known about the profile of large deletional mutations involving the β-globin gene. In this study, we aimed to screen common deletional mutations in the β-globin gene cluster in patients for whom direct DNA sequencing was not able to demonstrate the mutation(s) responsible for the disease phenotype.

MATERIALS AND METHODS

Thirty-one index cases selected with a series of selection events among 60 cases without detected β-globin gene mutation from 580 thalassemia-related cases tested by direct sequencing over the last 4 years in our diagnostic center were screened for the most common 8 different large deletional mutations of the β-globin gene cluster by gap-PCR.

RESULTS

We detected 1 homozygous and 9 heterozygous novel unrelated cases for the Turkish inversion/deletion (δβ)0 mutation in our series of 31 cases. Our study showed that the Turkish inversion/deletion (δβ)0 mutation per se accounts for 16.6% of the unidentified causative alleles and also accounts for 1.5% of all detected mutations over the last 4 years in our laboratory.

CONCLUSION

Since molecular diagnosis of deletional mutations in the β-globin gene cluster warrants different approaches, it deserves special attention in order to provide prenatal diagnosis and prevention opportunities to the families involved. We conclude that the Turkish inversion/deletion (δβ)0, as the most prevalent deletional mutation detected so far, has to be routinely tested for in Antalya, and the gap-PCR approach has valuable diagnostic potential in the patients at risk.