RARB and pachyonychia congenita: We observed hypermethylation of GSTP1, but also of other genes well known to be hypermethylated in PC, including AOX1, APC, BARHL2, CCDC8, CDKN2A, CYP27A1, EFS, GRASP, HOXA3, HOXC11, HOXD3, KIT, NXK2-1, NXK2-5, PHOX2A, POU3F3, PTGS2, RARB, RHCG, SIX6, TBX15, TMEM106A, WNT2, and ZNF154 [15] (Additional file 4: Table S1).