Already in 2003, Korponay-Szabo and coworkers [31] noted that the decrease in IgG anti-tTG antibody levels was slow in CD patients with IgA deficiency and most of them were still positive after more than two or three years on a GFD, in contrast to IgA competent CD patients where levels decreased markedly or returned to normal for IgG anti-tTG/DGP antibodies after one year on a GFD [32]–[34]. This evidence concerns the gene TGM2 and selective IgA deficiency disease.