CD79A and Decreased circulating total IgM: The ‘other PAD’ cohort included patients with isolated IgG subclass deficiency (n = 21), transient hypogammaglobulinemia of infancy (THI, n = 7), selective IgA or IgM deficiency (n = 2 and n = 1, respectively), specific antibody deficiency (SPAD, n = 31), class switch recombination defects and hyper-IgM syndrome (n = 1), and unclassified idiopathic primary hypogammaglobulinemia (n = 137) (Table 1).