For example, while eczema is with a prevalence of > 50% similarly frequent in patients with LOF mutations in FOXP3, CD25, STAT5B or GOF mutations in STAT3, autoimmune phenomena including cytopenia, thyroiditis and hepatitis as well as lymphoproliferations are characteristic for CD25 deficiency but occur in only less than 10% of patients with STAT5 deficiency [106, 129, 135, 139]. Here, STAT5B is linked to hepatitis A virus infection.