MCOLN1 and retinitis pigmentosa: In line with this, we also found reduced TRPML1 activity in Batten disease iPSC-derived cortical neurons (CLN3 knockout and CLN3D416G), the latter showing a severe clinical phenotype, while CLN3R405W resulted in a retinitis pigmentosa phenotype, presenting with a fully active TRPML1 channel (Figure 4).