GSTM1 and Schnyder corneal dystrophy: Hydroxyurea, which induces fetal Hb (HbF) to dilute HbS and thus prevent polymer formation, was the first drug approved in 1998 by the U.S. Food and Drug Administration (FDA) to treat SCD (Telen, 2016; Mvalo et al., 2018; FDA, 2019; Commissioner, 2020).