BMP2-independent inhibition of ECM mineralization by mosaic-activating MAP2K1 mutation. Affected and unaffected cells from Melo-18 (MAP2K1 p.K57N) were cultured in osteogenic media with or without recombinant BMP2. Alizarin Red S staining displays significant inhibition of ECM mineralization by mosaic-activating MAP2K1 mutation, regardless of the presence of BMP2 in osteogenic media. Data are representative of at least two independent experiments. Scale bar = 10 mm. Aff, affected; Unaff, unaffected.