Since it has been challenging to assemble sufficiently large and homogeneous SCD study cohorts, the first HbF loci, and thus the first SCD modifier genes, outside the beta-globin gene cluster, HBS1 like Translational GTPase-MYB Proto-Oncogene (HBS1L-MYB) and B-cell lymphoma/leukaemia 11A (BCL11A) were discovered through studies in an extended family [5] and large non-anaemic population samples [6–8]. This evidence concerns the gene HBB and Schnyder corneal dystrophy.