The invention relates to a composition comprising a sarcoplasmic/endoplasmic reticulum calcium ATPase pump inhibitor encapsulated in a polymer nanoparticle, for use in treating a disease caused by protein retention in the endoplasmic reticulum (ER). Further provided is a transgenic mouse carrying in its genome a heterologous nucleic acid that encodes an H338Y mutant gp91phox protein. The transgenic mouse can serve as a model for human chronic granulomatous disease.