From 31 investigated genes involved in retinol metabolism (most of which were discussed in the part I of this review [1]) SNPs of two genes were significantly more frequent in patients with PC, namely rs1330286 of ALDH1A1 (OR = 0.88, 95% CI: 0.83, 0.94; the expression quantitative trait loci (eQTL) of this gene) and rs4646653 of ALDH1A3 (OR = 1.17, 95% CI: 1.07, 1.27), with increased ALDH1A3 mRNA in PC tissue specimens than in healthy controls [46]. Here, ALDH1A3 is linked to pachyonychia congenita.