A Case of Misdiagnosis Caused by the Coinheritance of Hb G-Siriraj [β7(A4)Glu→Lys; HBB: c.22G>A] and Hb H Disease

Despite the fact that most hemoglobin (Hb) variants are clinically and hematologically silent, they can interact with thalassemias, which could sometimes give rise to complicated routine thalassemia diagnostics. Hb G-Siriraj [β7(A4)Glu→Lys; HBB: c.22G>A] alone is a benign condition, but its coinheritance with α-thalassemia (α-thal) may lead to misdiagnosis. We describe the case of a Chinese woman with an elevated Hb A₂ level who was assumed to carry heterozygous β-thalassemia (β-thal), but was later shown to be a double heterozygote for Hb G-Siriraj and Hb H disease. This study for the first time described hematological characteristics of a patient with a double heterozygosity for Hb G-Siriraj and Hb H disease. It is of great significance for technicians and clinicians to expand their knowledge as well as to help guide clinical diagnosis, population screening and genetic counseling.

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.