A New β-Thalassemia Mutation Produced by a Single Nucleotide Substitution in the Conserved Dinucleotide Sequence of the IVS-I Consensus Acceptor Site (Ag→AA)

Abstract

An Egyptian child with thalassemia major was found to carry two different haplotypes (I and VI) associated with two β-thalassemic chromosomes. Analysis with several oligonucleotides and restriction enzymes, which identify the mutations most common in the Mediterranean area, allowed the identification of only one mutation, namely T→C at position 6 of the first intervening sequence (IVS-I). In order to characterize the other mutation the β gene was amplified with polymerase chain reaction and sequenced. A G→A substitution was found at position 130 of the IVS-I which alters the conserved dinucleotide AG present in the consensus acceptor sequence, thus producing a βd` -thalassemia. This mutation was further confirmed by restriction analysis since it creates a new restriction site for the enzyme Afl II. It is concluded that this subject carries the IVS-I-6 mutation associated with haplotype VI, frequently observed in Mediterranean areas, and a new mutation at the acceptor site of the IVS-I, which has not been described before, associated with haplotype I. This thalassemic gene can be added to the list of mutations that can be identified by Southern analysis using Afl II.