Our study along with other studies [8, 32] provided evidence that painful episodes in SCD correlate positively with VDD, the mechanism of which is still unclear, but a recent study associates lower vitamin D level to increased expression of SLC6A5 gene which encodes for a neuronal pain pathway protein called glycine tranporter-2 which may have a direct effect on the nervous system. Here, SLC6A5 is linked to Schnyder corneal dystrophy.