ALBERT

Description: Background: Fetal hemoglobin (HbF, α2g2) induction is known to reduce the clinical complications of sickle cell anemia (SCA). Progress in identifying novel HbF inducing strategies has been slowed by an incomplete understanding of gamma-globin regulation. We have used natural genetic variation to identify novel genes and pathways associated with HbF levels in patients with SCA, beginning with whole exome sequencing (WES). This approach identified FOXO3, a transcription factor important for insulin signaling and erythroid maturation, among other functions, as a positive regulator of HbF. We then confirmed the role of FOXO3 in HbF regulation with functional studies in erythroid culture (Zhang, Blood 2018). To overcome the limitations of WES, namely the absence of regulatory and promotor sequencing data, we performed whole genome sequencing (WGS) on 658 pediatric SCA patients, and analyzed the data for common variants predictive of HbF levels. Methods : WGS was performed on a cohort of 658 pediatric patients with HbSS and HbSβ0 with IRB approval from Texas Children's Hospital, and from St Jude Children's Research Hospital, as part of the Sickle Cell Clinical Research and Intervention Program (Hankins et al 2018). Baseline HbF levels, not on hydroxyurea therapy, was measured by HPLC. Subjects were between 6 months and 21 years of age from both institutions; 52% were male. We used mixed linear regression models to screen for variants associated with transformed HbF values, and performed ridge regression with 10-fold cross-validation to confirm associations after adjustment for HBG and BCL11A-associated variants, age, sex, and race (determined by principal components analysis). Hematopoietic stem and progenitor cells (HSPCs) from 3 patients (all HbSS) were treated with recombinant human IGFBP3 (1µg/ml) beginning on day 7 of two-phase culture. Effects of IGFBP3 on gamma-globin expression were evaluated by RT-qPCR, and on HbF levels by HPLC, on days 14 and 21 of culture. The effects of IGFBP3 on known modifiers of HbF and the FOXO3 pathway were assessed by RT-qPCR and western blot on day 21 of culture. Erythroid maturation was assessed by flow cytometry using anti-CD71, GPA, and Band3 on day 21 of culture. Results: Our whole genome sequencing data identified a strong association between all 11 variants 200 kb upstream of IGFBP3 and baseline HbF levels (p