Interestingly, exogenously added CTSL could at least in part clear that accumulated proteinaceous material such as saposin or repair the autophagic impairments in Ctsd knockout neuronal stem cell-derived astrocytes and mice, a model for neuronal ceroid lipofuscinosis [23], suggesting a compensatory function between CTSD and CTSL. The gene discussed is CTSD; the disease is neuronal ceroid lipofuscinosis.