A recent study showed that the IgA1+ microbiota fraction in patients with CD was notably enriched in beneficial commensals and that local IgA2 selection of the microbiota correlated with disease activity in CD, suggesting that IgA1 has a pathogenic role in the lumen in CD, whereas IgA2 has a pathogenic role in tissues (91). Here, IGHA1 is linked to Cowden disease.