FZD9 and Hand-foot syndrome: In HFs at the anagen stage and catagen stage, we further analyzed the protein–protein interaction (PPI) network of core KEGG pathways and identified 20 genes, namely TGFB2, FGF13, TYR, WNT7B, WNT7A, WNT16, FZD1, FZD9, THBS2, TNC, ITGA2, ITGA5, SFRP1, NTRK2, INSR, KDR, CSF1, PDGFA, FGFR1, and PDGFRA, that may participate in HF development and growth (Figure 3D).