An Unexpected Finding of a Novel 21.9 kb Deletion (Heyuan deletion, β21.9kb) β-Thalassemia During HbA1c Measurements.

Abstract

Background: β-thalassemia is predominantly caused by point mutations in the β-globin gene, whereas large deletions occur less frequently. Here, we described a novel 21.9 kb deletion found in a patient with β-thalassemia dur-ing HbA1c measurements.

Methods: The proband was a 25-year-old female who came to the hospital with her husband for routine prenatal examinations. The hemoglobin A1c(HbA1c) was measured by high-performance liquid chromatography (HPLC). Hb analysis was performed by capillary electrophoresis (CE). Routine genetic analysis was carried out by PCR and reverse dot-blot (PCR-RDB) and Gap-PCR. Multiplex ligation-dependent probe amplification (MLPA) was used to screen the deletion in the β-globin chain. Based on the MLPA results, the break location of the deletion was determined by third-generation sequencing (TGS). Sanger sequencing verified the breakpoint in the Gap-PCR amplification products of TGS.

Results: HbA1c measurements suggested an elevated HbF value (> 5%) by HPLC, and a retest of the Hb analysis showed an HbF value of 27.9%, and an Hb A2 value of 1.7% using CE. No mutations were detected by Gap-PCR and PCR-RDB. However, MLPA demostrated the presence of large fragment deletion in the β-globin chain. The positions of the deletion were located between 5,225,669 and 5,247,554 on chromosome 11 (chr11: 5,225,669-5,247,554; NG_000007.3:g.50,063-71,947 del) using TGS, spanning the length of 21,886 bp (21.9 kb deletion).

Conclusions: This is the first report of the 21.9 kb deletion, so we named it Heyuan deletion for the place of origin of the proband. It presented with normal hematological parameters but an elevated HbF value.