Both of these genes have been the subject of investigation in SIgAD: a role for missense TACI variants in SIgAD has been proposed and disputed in the literature [41,45] whilst the APRIL SNP rs3803800 has previously tested negative for association with SIgAD in two small cohorts of 164 and 51 patients [172]. This evidence concerns the gene TNFSF13 and selective IgA deficiency disease.