CDC73 and pachyonychia congenita: The absence of parafibromin nuclear staining, detected by IHC analysis, has been reported to occur in 15% of APAs, and <5%–20% of PAs, and it seems that the ability to distinguish between PC, APA, and PA using parafibromin IHC appears to be lower than CDC73 mutational analysis (Tan et al., 2004; Gill et al., 2006; Juhlin, et al., 2006; Cetani et al., 2007; Guarnieri et al., 2012; Cetani et al., 2013; Hu, Liao, Cao, Gao, & Zhao, 2016).