Although gene replacement therapy using a viral vector has been applied for genetic neurological diseases, simple replacement cannot be used to treat PMD caused by gain-of-function mutant PLP1. We searched for small molecules that improve the cellular localization of mutant PLP1 in stably transfected MO3.13 cells by visualizing the cellular localization of PLP1 and subsequently identified piracetam. The gene discussed is PLP1; the disease is Pelizeaus-Merzbacher spectrum disorder.