CD8+ and CD4+ T cells are activated in the peripheral blood of patients with adenosine deaminase 2 deficiency, and T cells show significant cell-cell interaction with monocytes, which promote the upregulation of signal transducer and activator of transcription 1 (STAT1) expression in T cells (28). The gene discussed is STAT1; the disease is hyperinsulinemic hypoglycemia, familial, 4.