Hemoglobin F Only Syndrome at Birth: A Case of Maternal HbA2' Complicating the Diagnosis of β-Thalassemia

A Case Report of Compound Heterozygosity for β0/β+-Thalassemia Resulting from under Diagnosed β-Thalassemia Found in a Hb A'2 Sample

Hb A'₂ (or Hb B₂) (HBD: c.49G>C) is the most frequent δ chain variant that has been described in Africa but not in Thailand. We report here a 10-month-old Thai infant with compound heterozygosity for β⁰ codon 17 (A>T; HBB: c.52A>T) and β⁺ IVS II-654 (C>T; HBB: c.316-197C>T). Under diagnosed β-thalassemia (β-thal) in her father, who carries Hb A'₂ and a heterozygous β⁰ codon 17 mutation, and the mother, who carries a heterozygous β⁺ IVS II-654 mutation, was noted. Although Hb A'₂ does not cause any problems, heterozygosity for Hb A'₂ can lead to under diagnosis of β-thal in Hb A'₂ samples. This case highlights the importance of Hb A'₂ in prenatal diagnosis (PND). Thus, molecular analysis for β-thal mutations should be carried out when a small peak presents at the retention time (RT) of 4.71 min. on high performance liquid chromatography (HPLC) and the summation level of this peak and Hb A₂ was equal or higher than 4.0%.