Hence, given that IgA constitutes only a minor component of the FDA-approved Ig replacement products, and the fact that Ig replacement products are derived from human plasma/serum, a site where IgA exists as a monomer rather than as sIgA, the resultant GI pathology and the progression to CLD in many patients with B cell IEI, despite lifelong Ig replacement therapy, is not surprising [85,90,91]. This evidence concerns the gene CD79A and congenital secretory chloride diarrhea 1.