Identification of nondeletional α-thalassemia in a prenatal screening program by reverse dot-blot in southern China

Polymorphisms of α-Globin Genes Compromise Polymerase Chain Reaction-Based α-Thalassemia Genotyping in Three Chinese Families

In practice, gap-polymerase chain reaction (gap-PCR) and reversed dot-blot are the two most frequently used molecular diagnostic methods for α-thalassemia (α-thal) genotyping. Here, we describe three Chinese individuals from three unrelated families in whom a polymorphism on the α-globin gene cluster led to diagnostic pitfalls. During general molecular diagnosis of thalassemia, three individuals with unexplained results were found. Blood or chorionic villus samples were collected from these three individuals and their family members. Hematological investigations and genetic tests were performed. In Family 1, a polymorphism of HBA2: c.301-24delinsCTCGGCC at the annealing site of the forward primer used in the PCR-reverse dot-blot assay was identified, leading to allele drop-out during the PCR amplification process. In Family 2, a synonymous mutation of C>T substitution at codon 125 of the α2 gene (HBA2: c.376C>T) was identified, leading to the failure of PCR-reversed dot-blot for the HBA2: c.377T>C (Hb Quong Sze or Hb QS) mutation. In Family 3, the size of the PCR fragment from the α2-globin allele carrying the HBA2: c.-771_-428del mutation was smaller and nearly equal to the size of the fragment corresponding to the -α^4.2 (leftward) deletion; we also found that the HBA2: c.-771_-428del mutation was linked to a known HBA1: c.-673A>G mutation in this family. In conclusion, diagnostic errors may be caused by technical pitfalls or inherent properties of the DNA sample. All logical steps should be taken to monitor and thus preclude such events.

Results of Coexistence of β-Thalassemia Minor in Hb H Disease Patients

The aim of this study was to determine the hematological characteristics in a large group of Hb H (β4) patients with or without a coexisting β-thalassemia (β-thal), identified by a thalassemia screening program in mainland China. A total of 361 patients with Hb H disease were found, including 343 with deletional types and 18 with nondeletional types. β-Thalassemia was found in 28 (7.8%) out of the 361 Hb H cases, and all of the 28 cases had the deletional type of Hb H disease. Lower hemoglobin (Hb) levels were detected in cases with the nondeletional type compared to those in cases with the deletional type. β-Thalassemia significantly increases the Hb levels in Hb H cases. The Hb H and Hb Bart's (γ4) fractions were visible in 270 (85.7%) and 122 (38.7%) out of 315 deletional type cases, respectively, while no Hb H or Hb Bart's fractions were detectable in 28 deletional type cases with β-thal. Therefore, the diagnosis of Hb H disease in a β-thal carrier is challenging. Molecular analysis of α- and β-globin genes is imperative in all cases with a β-thal trait.