NAP1L5 and Pelizeaus-Merzbacher spectrum disorder: In the biparental-PMD specimens, seven of 15 (46.7%) placenta-specific DMRs (MCCC1, AIM1, AGBL3, GLIS3, FAM196A, N4BP2L1, and FAM20A) were aberrantly hypomethylated in more than half of the specimens, whereas five of 25 (20.0%) gametic maternally methylated ubiquitous DMRs (PPIEL, NAP1L5, GRB10, NESPAS-GNASXL, and WRB) were aberrantly hypomethylated in more than half of the specimens (Tables 2 and 3, Additional file 1: Table S1).