In summary, all these analyses demonstrated a robust and significant causal relationship between 13 immune cells and ADHD, including CD40 on monocytes, CD27 on memory B cell, CD27 on sw mem, CD4 on activated Treg, CD3 on naive CD8br, SSC-A on monocyte, IgD on IgD+ CD24+, CD40 on CD14+ CD16+ monocyte, CD27 on IgD- CD38dim, CD40 on CD14− CD16+ monocyte, CD40 on CD14+ CD16− monocyte, CD27 on unsw mem, and SSC-A on CD14+ monocyte. Here, CD27 is linked to attention deficit-hyperactivity disorder.