Cystic fibrosis, sickle cell anemia, Huntington’s disease and phenylketonuria are all examples of disorders caused by the mutation of a single nucleotide, a building block of DNA. The human DNA consists of approximately 3 billion nucleotides of four types: Adenine (A), cytosine (C), guanine (G), and thymine (T). In some cases, the difference of just one nucleotide can bring serious consequences. Scientists hope to cure these diseases by substituting the incorrect nucleotide with the correct one. However, it is technically challenging to replace a single nucleotide with the current gene editing tool, CRISPR-Cas9. Scientists at the Center for Genome Engineering, within the Institute for Basic Science (IBS) have used a variation of the popular gene editing technique CRISPR-Cas9 to produce mice with a single nucleotide difference. Their findings are published in Nature Biotechnology.