In Xenopus, RSPO3 has been shown to interact with Syndecan4 to induce non-canonical (PCP) signalling (Ohkawara et al., 2011) and Syndecan1 has been suggested to present WNT and R-spondins in multiple myeloma (Ren et al., 2018). This evidence concerns the gene RSPO1 and plasma cell myeloma.