The large intra-group differences among SCD samples and mismatches between groups may explain some of the inconsistent results; for example, the age span of SCD subjects in one study reached 31 years, from 53 to 84 years old [34], and in another study, the presence of the APOE ε4 allele in the SCD subjects was 0%, while it was 52% in the NCs [30]. The gene discussed is APOE; the disease is Schnyder corneal dystrophy.