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

Abstract

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.

Figure 1. Representative samples of Turkish-type inversion/deletion (δβ)0 mutation detected by gap-PCR. For reaction A testing the upstream breakage of the mutation, the upper band (742 bp) corresponds to normal results and the lower band (432 bp) to the mutation. Case 4 and Case 5 are heterozygous as both have normal and mutation-related polymerase chain reaction fragments. For reaction B testing the downstream breakage of the mutation, the upper band (700 bp) corresponds to normal results and the lower band (489 bp) to the mutation. Cases 4, 5, 6, and 7 show both normal and mutation-related polymerase chain reaction fragments, confirming that they are heterozygous for the mutation. NS: Normal sample, N: normal, M: mutation, 252x91 mm (72x72 dpi).