Misdiagnosis of a beta-thalassemia heterozygote using a reverse dot-blot method may be caused by a polymorphic locus in the wild type sequence of the beta-globin gene.

Reverse dot-blot is an effective method for detecting beta-thalassemia (beta-thal) mutations. In this study, we report the cause of a misdiagnosis by reverse dot-blot. One patient with a beta-globin genotype that was initially diagnosed as a codon 17 (A>T) homozygote by reverse dot-blot at our Clinic, was later shown to be a codon 17 (A>T) heterozygote by direct sequencing of the amplified fragment and by sequence analysis of a recombinant T vector plasmid containing an amplified fragment of the beta-globin gene. A polymorphic locus around the mutation site within the haploid DNA that lacked the codon 17 mutation was identified. This result suggests that when reverse dot-blot is used for the genetic diagnosis of beta-globin, polymorphic loci around the mutation site should be taken into consideration, and more allele specific oligonucleotide probes should be designed according to the polymorphic loci.