PIK3CA and nicotine dependence: The enrichment analyses showed pathways involved in signal transduction (MAPK signaling pathway, PI3K-Akt signaling pathway, Ras signaling pathway), cellular adhesion and movement (focal adhesion, ECM-receptor interaction, regulation of actin cytoskeleton, cell adhesion molecules), and neuronal system (axon guidance, neuroactive ligand-receptor interaction, glutamatergic synapse, synapse vesicle cycle, morphine addiction, and nicotine addiction), among others.