In an Italian survey of 696 cases of SCD, conducted in the late 1990s, 518 cases (74%) were identified as compound heterozygous HbS/ß-thalassemia, 149 cases (21%) as homozygous HbSS, and 21 cases (3%) as compound heterozygous HbS/other Hb structural variant [26]. This evidence concerns the gene GSTM1 and Schnyder corneal dystrophy.