PER1 and pachyonychia congenita: Zhu et al. found four variants associated with risk of developing PC (Table 1), but also an additional four SNPs that were associated with the risk of a more aggressive tumor (CLOCK 11133373, NPAS2 rs895521, PER1 rs885747 and PER1 rs2289591 variants) and eight SNPs that were significantly associated with risk of less aggressive PC (PER3 rs1012477, CRY2 rs2292912, BMAL1 rs7950226, NPAS2 rs17024926 and rs1369481, CSNK1E rs1534891, CRY1 rs12315175 and PER2 rs7602358) in Caucasian men [49].