FCER2 and inborn error of immunity: These results suggest that AIOLOS/Aiolos plays an important role in regulation of CD21 and CD23 expression on B cells, and decreased CD21 and CD23 expression represents a potentially useful and sensitive screen for similar patients (e.g., was detected in all AIOLOS N160S affected individuals, but not in healthy controls), although its specificity (e.g., prevalence in all other primary immunodeficiency/inborn errors of immunity) has yet to be formally determined.