SUPT5H mutations associated with elevation of Hb A₂ level: Identification of two novel variants and literature review

β-thalassemia is one of the most common monogenic disorders in areas of the tropics and subtropics, which represents a major familial and social burden to local people. The elevated Hb A₂ level, generally specified as greater than 3.5 %, is commonly used as a high efficiency index for screening of β-thalassemia carriers. However, mutations in other genes such as GATA1 and KLF1, could also result in increased Hb A₂ level. In this study, we identified two novel variants in the SUPT5H gene: a frameshift mutation (SUPT5H: c.3032_3033delTG, p.M1011Mfs*9) and a nonsense mutation (SUPT5H: c.397C > T, p.Arg133*) in two Chinese individuals. Utilizing a combination of phenotype analysis, bioinformatics analysis, and functional analysis, we deduced that these two variants modified the SUPT5H protein's structure, thereby impacting its function and consequently leading to the heightened Hb A₂ level phenotype found in the carriers. Furthermore, through a comprehensive literature review, a mutation spectrum was consolidated for SUPT5H, an investigation into the genotype-phenotype correlation was conducted, and factors known to influence Hb A₂ levels were identified. Based on this in-depth understanding, clinicians are better equipped to carry out large scale screenings in regions with high prevalence of β-thalassemia.