ERG and pachyonychia congenita: The results from our parallel IHC analyses of 5mC, 5hmC, 5fC, and 5caC in NM and PC tissue samples from more than 500 RP patients support the notion that epigenetic deregulation is a molecular hallmark of PC, and furthermore suggest that PC-associated epigenetic reprogramming differs between ERG+ and ERG− PCs.