SPHK1 and Schnyder corneal dystrophy: Moreover, we found substantially increased steady state levels of multiple intermediates of PPP including glucose 6-phosphate (G6P), gluconate-6-phosphate (6-P-gluconate), ribose 1-phosphate (R1P), erythrose 4-phosphate (E4P) and sedoheptulose 7-phosphate (S7P) in the erythrocytes of SCD/Sphk1−/− mice relative to SCD mice (Fig. 2b,c), suggesting that the PPP is significantly enhanced in SCD/Sphk1−/− erythrocytes.