We assessed the abundance of GαsR201C/H-expressing cells in FD tissue before and after treatment with denosumab via the novel technique BasescopeTM using biopsies from a phase 2 clinical trial.4 First, in collaboration with ACD, we used cultured bone marrow stromal cells (BMSCs) from FD patients harboring the GNAS p.R201C and p.R201H variants and from healthy wild-type (WT) volunteers to select, optimize and validate probes specific for the WT Gαs, GαsR201C and GαsR201H mRNAs (Fig. S1). Here, GNAS is linked to Fabry disease.