PTBP1 and Salla disease: Downregulation of PTBP1 reduced both PKLR mRNA and protein in NOZ and SGC-996 cells, and knockdown of PTBP1 abrogated the effect of overexpressed circFOXP1 on PKLR expression in GBC-SD cells (Additional file 10: Figure S7A and Fig. 6f).