CD40LG and selective IgM deficiency: Selective immunoglobulin (Ig) M deficiency (SIGMD) was defined as having a serum immunoglobulin IgM level that is repeatedly below 2 standard deviations of normal while maintaining normal levels of serum IgA, IgG, and IgG subclasses without associated T-cell defects or external factors that can be linked to the condition.2 Since the literature is limited on AILD associated with SIGMD, here we present the clinical features and prognosis of our 4 patients.