Complex sentence: It is a pleiotropic growth factor protein, which is associated with tumorigenesis (the emergence of cancer) when overproduced, however deficit in progranulin is associated with frontotemporal lobar degeneration.
Split into simpler sentences: It is a pleiotropic growth factor protein, which is associated with tumorigenesis (the emergence of cancer) when overproduced. However deficit in progranulin is associated with frontotemporal lobar degeneration.