Highly conserved sequences are typically associated with proteins that underpin conserved or essential metabolic activities (Zhao et al., 2018), and mice that are IGF1-null (created by homologous recombination), exhibit postnatal lethality, growth retardation, infertility, and profound defects in the development of their major organ systems, with this confirming the essential nature of the protein's activity (Liu et al., 2000). Here, IGF1 is linked to Infertility.