We also found a negative correlation between the expression levels of AFP and FNDC4, although the correlation was not high, and the expression of FNDC4 was negatively correlated with other liver cancer-related genes, such as Glypican 3 (GPC3), Midkine (MDK) and Dickkopf WNT signaling pathway inhibitor 1 (DKK1). The gene discussed is MDK; the disease is liver cancer.