CKB and pachyonychia congenita: Among 18 studies including CKB, involving 4.1 million individuals with 13,072 cases of PC, previously diagnosed diabetes was associated with a 52% (RR = 1.52 [1.43–1.63]; n = 18) increased risk of PC, with moderate heterogeneity between studies (I2 = 49%, Cochran's Q p = 0.01; Fig. 2).