Glycine supplementation ofthe culture medium significantly increases PPIX accumulation in HeLa cells expressing delAGTG. Plus (+) signs indicate samples in which the culture medium was supplemented with 100 glycine, and minus (−) signs indicate samples in which no glycine was added. The graph bars correspond to the results with wild-type hALAS2 (blue), delAT (green), delAGTG (pink), and Q548X (purple). Mean PPIX fluorescence values are representative of three separate experiments ± standard deviation (*p<0.05 and **p<0.01, Student’s t-test) [a.u., arbitrary units].