Molecular Characterization and Hematological Aspects of Hb E-Myanmar [β26(B8)Glu→Lys and β65(E9)Lys→Asn, HBB: c.[79G>A;198G>C]): A Novel β-Thalassemic Hemoglobin Variant

A Triple-Heterozygous β-Thalassemia Patient Demonstrated an Unusual Electrophoresis Pattern Due to a Novel β0 Mutation [an IVS-II-654 (C>T) mutation with a Hb Zürich-Langstrasse (HBB: c.151A>T) mutation in cis]

β-Thalassemia (β-thal) is caused by mutations on the β-globin genes, causing reduced (β⁺) or absent (β⁰) synthesis of the β chains of hemoglobin (Hb). In this report, a 28-year-old male patient with anemia and jaundice, was diagnosed with triple-heterozygous β-thal [an IVS-II-654 (C>T) mutation, a Hb Zürich-Langstrasse (HBB: c.151A>T) mutation and a Hb G-Siriraj (HBB: c.22G>A) mutation] by gene sequencing. However, his electrophoresis pattern was unusual: 90.8% Hb G-Siriraj, 5.9% Hb A₂, 3.3% Hb F, no Hb A, no Hb Zürich-Langstrasse. His mother carried a β-thal trait (β^A/β^IVS-II-654) having mild anemia, with a classical electrophoresis pattern (95.1% Hb A, 4.4% Hb A₂, 0.5% Hb F). His father was heterozygous for Hb G-Siriraj (β^A/β^G-Siriraj) but asymptomatic, with a corresponding electrophoresis pattern (63.9% Hb A, 3.5% Hb A₂, 32.6% Hb G-Siriraj). In view of the family study results, the Hb Zürich-Langstrasse mutation in the proband was considered a de novo mutation occurring on the β^IVS-II-654 allele that he inherited from his mother, resulting in a β^{IVS-II-654/Hb Zürich-Langstrasse} genotype, which should be interpreted as a novel β⁰ mutation. This report illustrates that mutations in cis can confound genotype-phenotype correlations, therefore, just as DNA testing and Hb analysis, family study is also indispensable to the accurate identification of β-thal mutations.