The single-domain molecule-based assay showed that the APS serum samples depended mainly on DI, DV, and DII, slightly on DIV, and not at all on DIII.<h4>Conclusions</h4>Serum IgG from both classified and non-classifiable APS may react with other β2GPI domains than DI and DIV-V. Here, APOH is linked to autoimmune polyendocrinopathy.