HPD and Hypertyrosinemia: Its inhibition of HPPD (Figure S1) has been shown to dramatically reduce the circulating concentration of HGA,1, 4, 5, 6, 7, 8 but leads to marked hypertyrosinemia.1, 4, 5, 6, 7, 8, 9, 10 Beyond hypertyrosinemia, there is very little reported on the biochemical consequences of nitisinone therapy.