The Clinical Significance of the Spectrum of Interactions of the Rare IVS-II-5 G>C (HBB: c.315+5 G>C) Variation with Other β-Thalassemia Mutations in Southern China

Background: IVS-II-5 G>C (HBB: c.315+5 G>C) is a rare β-thalassemia mutation. However, there is no clear evidence regarding the effect of this defect or co-inheritance of other β-thalassemia mutations on phenotypes.

Methods: The clinical phenotypes associated with compound heterozygosity for the IVS-II-5 G>C mutation and other β-thalassemia mutations, together with the genetic modifiers' potential effect of the genetic modifiers α-thalassemia, were studied in 13 patients. In addition, analyses of red cell indices, hemoglobin component, iron status, and α-globin genes were carried out in 19 heterozygotes.

Results: Next-generation sequencing of 24 undiagnosed patients with transfusion-dependent thalassemia (TDT) or non-transfusion-dependent thalassemia (NTDT) identified 13 carriers of the IVS-II-5 G>C mutation. There was a wide spectrum of phenotypic severity in compound heterozygotes and 6 (46.2%) of 13 were transfusion dependent. Analysis of 19 heterozygotes indicated that most were hematologically normal without appreciable microcytosis or hypochromia, and approximately half had normal hemoglobin A₂ levels at the same time.

Conclusion: Compound heterozygotes for IVS-II-5 G>C and other severe β-thalassemia mutations are phenotypically severe enough to necessitate appropriate therapy and counselling. Co-inheritance of this nucleotide substitution with other β-thalassemia mutations may account for a considerable portion of the incidence of undiagnosed patients with NTDT and TDT in Guangxi. Therefore, the IVS-II-5 G>C mutation can pose serious difficulties in screening and counselling.