CIITA and selective IgA deficiency disease: Whilst this gene has no clear role in driving IgA levels, the associated SNPs were downstream of two candidate genes (Fig 6; S7 & S8 Tables; distances of ~1.021Mb and ~709Kb, respectively): the Class II Major Histocompatibility Complex Transactivator (CIITA), which is described as a “master control factor” for gene expression at the major histocompatibility complex [65,66]; and C-Type Lectin Domain Containing 16A (CLEC16A), variants at which have been associated with common variable immunodeficiency disorder and IgA deficiency [67–69].