PLP1 and Pelizeaus-Merzbacher spectrum disorder: Genomic duplications of the PLP1 (proteolipid protein 1) gene is one of the main causes of PMD, and has been used to molecularly diagnose the disease by interphase FISH and quantitative multiplex PCR methods using blood samples in children and adults (Lee et al. 2005; Inoue et al. 1996).