ICOS and selective IgA deficiency disease: This KEGG pathway analysis contained the following genes with a P value <0.05 in the IgA deficiency meta-analysis: genes encoding inflammatory and immunoregulatory cytokines (IL-2, IL-4, IL-6, IL- 10, IL-15, APRIL, BAFF), genes encoding B and T cells surface molecules (TACI, CD40, IL-15R, CD28, ICOS, ICOSLG), genes encoding gut-homing receptors on lymphocytes (ITGA4, CCR9, MADCAM-1, CXCL12, CCL28, LTβR, MAP3KI4) and genes encoding a DNA deaminase (AID) which is required for B cell class switch recombination.