KLK3 and pachyonychia congenita: The earliest biochemically confirmed case of PC occurred in present-day Siberia in the seventh century BC as found in mummified remains of an Iron Age Scythian king exhibiting bone lesions compatible with PC bone metastases.8 Biochemical confirmation was performed by detecting positive antibodies against prostate-specific antigen (PSA) and PSA-bound alpha1-antichymotrypsin.8 A biochemically unconfirmed case was found as early as 4500 years BC, also in Siberia.8