SPHK1 and Miyoshi myopathy: We found that the active form of SphK1 protein (phospho-SphK1) is highly expressed in MM cell lines (Figure 1C left panel) and positively correlates with GFI1 protein levels (r = 0.74) (Figure 1C right panel), while SGPP1 mRNA displayed a negative correlation (r = −0.961) with GFI1 mRNA in five different MM cell lines (Figure 1D).