Analysis of rare thalassemia caused by HS-40 regulatory site deletion

Objectives: To investigate the effect of HS-40 regulatory site deletion on α-globin gene expression and its clinical significance. Methods: Venous blood samples of subjects were analyzed using a hematology analyzer and high- performance liquid chromatography; fetal cord blood was analyzed by a capillary electrophoresis analyzer. Gap-polymerase chain reaction (PCR), reverse dot blot (RDB), and multiple-link-dependent probe amplification (MLPA) were used for genotyping of thalassemia. Results: The proband was POLR3 K, HS-40 heterozygous deletion; the proband's wife was -SEA/αα; the fetus was POLR3 K, HS-40 heterozygous deletion combined with -SEA deletion; all of them had microcytic hypochromic anemia. Fetal umbilical cord blood electrophoresis revealed a suspected Hb Bart's band to be 88.4%, and the fetus was, thus, diagnosed as Hb Bart's fetus. The red blood cell parameters of the sporadic case showed that he had microcytic hypochromic anemia. Hemoglobin (Hb) electrophoresis analysis showed Hb H to be 5.3%, leading to a diagnosis of Hb H disease. Gap-PCR and RDB identified the genotype to be -α3.7/αα, β A /β A . MLPA detected heterozygous deletion or -α3.7 deletion on one allele and deletion of the HS-40 regulatory site on the other allele. Conclusion: The deletion of HS-40 regulatory site reduced expression of α-globin. HS-40 heterozygous deletion manifested as mild anemia, which was of microcytic hypochromic type. When compounded with -α3.7/αα, it manifested as Hb H disease; and when compounded with -SEA/αɑ, it manifested as Hb Bart's fetus.