Using a newly developed gene editing system that relies on cellular machinery used by bacteria to defend themselves from viral infection, researchers from Massachusetts Institute of Technology have successfully treated mice with hereditary tyrosinemia type I, a rare and fatal liver disorder caused by a single genetic mutation (Yin H et al. Nat Biotechnol. doi:10.1038/nbt.2884 [published online March 30, 2014]).
The system, called called CRISPR (clustered, regularly interspaced, palindromic repeats), uses the DNA-cutting enzyme Cas9 bound to a short RNA guide strand that binds to a specific genetic sequence—in this case, within the FAH gene, which encodes the enzyme fumarylacetoacetate hydrolase (Fah). Patients with hereditary tyrosinemia type I have a mutation in the FAH gene and cannot break down the amino acid tyrosine. A 199-nucleotide DNA template that includes the correct sequence of the FAH gene is also delivered so that cellular machinery can copy this sequence as it introduces new genetic material where Cas9 has made its cut.