An unusual transfusion-dependent hemoglobin H disease caused by a novel complex inverted duplication involving the α-globin regulatory elements and α-thalassemia--SEA deletion.

Abstract

Four multi-species conserved sequences (MCSs) are important enhancers which affect α-globin expression. Deletions of MCS can cause α-thalassemia. So far, duplication of MCS has never been reported to account for thalassemia. In this study, an unusual transfusion-dependent case of hemoglobin H disease was identified by whole-genome sequencing, optical genome mapping and longer PCR with special primers, which was caused by a familial 96,620-bp inverted duplication (from MCS-R1 to MCS-R4), inserted between chr16:199348 and 199349 (GRCh37/hg19) within MCSs. The duplication segment included an inverted repeat sequence from chr16:102712 to176193 and one direct repeat sequence from chr16:176208 to 199348. The associated α-thalassemia trait was confirmed to result from disrupted topological chromatin domains using ATAC-seq and the dual‑luciferase reporter assay system. This case presents a new mechanism of α-thalassemia, and may aid our understanding of the effects of enhancers on gene expression and the differential contribution of the four enhancer elements in the human a-globin locus.