The database search identified 149 citations; as shown in our flowchart (Figure 1), we finally considered 44 articles, 42 of which were full papers [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52] plus one thesis [53] and one abstract [54] that examined the relationship between HC, MTHFR, and SCD and that were included in our systematic review and meta-analysis. Here, MTHFR is linked to Schnyder corneal dystrophy.