ABCD2 and X-linked adrenoleukodystrophy: In addition, we demonstrated that gene expression of ABCD2 is upregulated by overexpression of β-catenin/TCF-4 (Figs. 4A and 6A) while downregulation occurs by silencing of β-catenin (Figs. 4B and 7A) in both HepG2 cells and X-ALD fibroblasts.