In her study Elisabeth Salzer describes three novel monogenic diseases. For CD27 deficiency Elisabeth Salzer describes a large cohort of patients. Although all patients shared the same causative missense mutation, they displayed diverse clinical presentations. In another patient she was able to identify a mutation in PRKCD resulting in a primary immunodeficiency with severe Lupus-like autoimmunity. The patient exhibited increased mRNA levels of IL6. Therefore, treatment with Tocilizumab, a humanized anti-IL-6 receptor monoclonal antibody was suggested. In a family with a history of deaths due to inflammatory bowel disease she identified a missense mutation in IL21. She produced wild type and mutated IL-21 protein and demonstrated a loss of function phenotype. As IL-21 is in clinical trials, she proposed a potentially curative treatment option. These discoveries contributed to the understanding of the multifaceted regulatory mechanisms of the immune systemand highlighted essential players in these complex signaling networks.