COL4A4 and dentin dysplasia: Conversely, 24 collagen genes, including COL15A1 (Figure 2 and 3, Table 1), COL5A1, COL5A2, COL4A1, COL4A2, COL4A4 (Table S1), COL1A1, and COL3A1 (Figure S1) showed significantly higher level of expression in the DD patient-derived fibroblasts.