Yesterday’s announcement of the UK Human Fertilisation and Embryology Authority (HFEA)’s approval for genetically modifying human embryos marks a critical milestone in medical research. The research, which will be led by Dr Kathy Niakan at the Francis Crick Institute, focuses on studying how some of the genes that are active at the very early stages of embryonic development, can influence how embryonic stem cells differentiate into different types of cells and tissues, each having their specific functions. The studies proposed, aim to understand how particular abnormalities arising at these early stages can have an influence on infertility, miscarriage, and developmental disorders, and to identify potential therapeutic applications of stem cells. Balancing the highly contentious issues arising in both medicine and ethics is a truly tricky task. However, recent advances in gene editing have given hope to both patients and the many researchers working tirelessly to discover the molecular basis of genetic disorders and to develop treatments for over 7000 known rare diseases. Given that the majority of rare diseases can be attributed to a genetic defect and affect children, any technique that shows promise for ameliorating or preventing them is clearly of great interest to both the medical profession and patients alike.