The lack of SCA ICD-9-CM codes, ambiguous codes for Hb Sβ0 thalassemia vs Hb Sβ+ thalassemia, and the high rates of mismatch between true SCD genotype and the SCD ICD-9-CM codes in hospital discharge data may lead to the erroneous interpretation of such data and mistaken conclusions. This evidence concerns the gene GSTM1 and Schnyder corneal dystrophy.