DNMT1 preserves DNA methylation of ICRs and meiotic gene promoters in PGCs, and conditional deletion of Dnmt1 in PGCs was shown to cause a decrease in the number of germ cells and their precocious differentiation, including up-regulation of spermatogenesis- and meiosis-related genes in male and female germ cells, respectively, consequently leading to hypogonadism and infertility [27]. Here, DNMT1 is linked to hypogonadism.