Identification Of A Rare ?-Globin Gene Copy Number Variation In A Family

Background:a-globin gene copy number is closely related to the clinical severity of thalassemia.The clinical severity of ?-thalassemia is typically determined by the dosage of defect or loss of ?-globin genes,termed as silent ?-thalassemia(-?/??),mild microcytic hypochromic anaemia(--/?? or-?/-?),Hemoglobin H disease(--/-?)and Hb Bart's hydrops fetalis syndrome(--/--).Methods:After obtaining the consent,peripheral blood of the proband and family members including her parents and grandparents were collected.Hematological analysis and routine thalassaemia gene screening were performed firstly.MLPA and next generation sequencing(NGS)were used to detect the presence of copy number variation in the ?-globin gene cluster,digital droplet PCR(dd-PCR)was performed for more precise information about the CNV.Analysis of globin genes expression were mearsured in RNA level by qPCR and peptide chains in RBCs by high performance liquid chromatography(HPLC).Results:Hematologic profiles showed mild thalassaemia in the proband and her mother.Molecular diagnosis revealed that both the proband and her mother were Southeast Asian(--SEA)deletion carriers,and that the proband and her grandmother and father had a rare CNV mutation on the?-globin gene cluster,resulting in an increase of ?-globin gene copy number by more than 20 times.The repeat fragment was similar to aaaanti 4.2.According to RNA analysis and peptide chain analysis,we determined that the proband expressed lower? peptide chain than the ?,and presenting with mild ?-thalassaemia.But her grandmother and father as copy number variation carriers,with the unchanged peptide chain balance of ?/?,present normal.Conclusion:We reported a rare?-globin gene copy number variation in a Chinese family characterized with multiple copy number gains.It is worthy noting that such a CNV dose not alter the phenotypes of ?-thalassemia carrier.The detailed internal structure and the mechanism of the mutation both remains to be further studied.