The diagnosis and molecular analysis of a novel 21.9 kb deletion (Qinzhou type deletion) causing α+ thalassemia

α-Thalassemia is a common single-gene genetic disease that can cause Hb Bart's hydrops fetalis and Hb H disease in tropical and subtropical regions. When examining conventional thalassemia genes, an only detected --SEA genotype sample needs further analysis. In doing so, we found a novel 21.9 kb deletion (Qinzhou type deletion). The deletion position of the novel 21.9 kb deletion is from 14373 bp to 36299 bp of the α-globin gene cluster (NG_000006.1); thus, there exists a 21927 bp sequence deletion, into which a 29 bp sequence is added. After sequence analysis, a group of Gap-PCR primers were synthesized to diagnose this novel thalassemia genotype. Through pedigree analysis, we deduced that the propositus obtained the novel alleles from her mother. The genotype of this propositus is --SEA/-α21.9 and its phenotype conforms to the characteristics of Hb H disease, establishing that the combination between -α21.9 genotype and α0 genotype can lead to Hb H disease. By molecular analysis, we established that this case fits the characteristic of an α+ thalassemia genotype.