Among the genes involved in PC, ERG belongs to the “ERG subfamily” and contains a Pnt protein-interaction domain, while ETV1, ETV4, and ETV5 belong to the “PEA3 subfamily”, so called because of their close homology with the epididymal transcription factor polyomavirus enhancer activator 3 (PEA3), who was the first member of this group to be found and whose human homolog is ETV4 [19]. The gene discussed is ETV5; the disease is pachyonychia congenita.