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 : 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 (: c.376C>T) was identified, leading to the failure of PCR-reversed dot-blot for the : 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 : c.-771_-428del mutation was smaller and nearly equal to the size of the fragment corresponding to the -α (leftward) deletion; we also found that the : c.-771_-428del mutation was linked to a known : 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.