Antibodies from APS patient sera are able to bind BMP [13], and when endocytosed by BHK fibroblasts [13] and human endothelial cells [77] can affect the multifunctional insulin like growth factor/mannose-6-phosphate receptor (IGF2/MPR) [6,13,77], suggesting that BMP may be involved in APS pathogenicity [6]. Here, PGRMC1 is linked to autoimmune polyendocrinopathy.