As we mentioned above, vitamin D deficiency is quite common in this patient group (67–85%) and may appear in a more severe form although the single-nucleotide polymorphism (Apa I, VDR Fok I, Taq I) of the vitamin D receptor (VDR) does not correlate with the risk of developing PCOS or with the severity of the disease [31,32]. Here, VDR is linked to vitamin D deficiency.