Interestingly, in all the 10 PC samples characterized by a reduced number of TBX1-expressing cells, this molecular signature was associated with both the downregulation of TBX1 transcript and the loss of parafibromin immunostaining, while the 4 PC samples conserving parafibromin expression had TBX1 mRNA expression levels similar to those of normal parathyroid, suggesting a regulatory relationship between TBX1 and parafibromin, involved in parathyroid carcinogenesis. Here, TBX1 is linked to pachyonychia congenita.