PIK3CD and hepatitis B virus infection: Considering the molecular cascade effect, combining the genes of the above six sub-networks and conducting GO and KEGG analysis, it is clear that the modular gene is related to the methylation activation of mRNA splicing, mRNA processing and tRNA methylation (Figure 4A), and in addition, it is also involved in the PI3K-Akt pathway, viral carcinogenesis, mTOR signaling pathway, hepatitis B, and hepatitis C (Figure 4B).