http://www.digitaljournal.com/science/liver-disorder-in-mice-reversed-using-new-gene-editing-technology/article/379310

Liver disorder in mice reversed using new gene-editing technology

Posted Apr 2, 2014 by Sean Fraser
Researchers at the Massachusetts Institute of Technology have cured mice of a rare liver disorder that is caused by a single gene mutation using a new genome-editing technique.
Lab Mouse
Lab Mouse
wikipedia
The March 30 issue of Nature Biotechnology details the breakthrough in genetic engineering where researchers used a technique called CRISPR to cut out the section of the mice's DNA that mutated and replacing it with the right sequence.
CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats, and were first discovered in bacteria in 1987. CRISPRs are used by bacteria to defend themselves against viral infections. Researchers discovered that they can be used in tandem with a "cleaving" enzyme called Cas9 to snip out mutated sections of a genome.
The CRISPR-Cas9 complex, as it is referred to, uses a short RNA "guide strand" to replicate the proper sequence to replace the cut out piece.
"What's exciting about this approach is that we can actually correct a defective gene in a living adult animal," said Daniel Anderson, an Associate Professor of Chemical Engineering at MIT. Anderson also was the senior author of the paper.
The CRISPR-Cas9 complex was revealed in February of this year.
"We've come to view the Cas9 complex as the ultimate guided missile that we can use to target precise sites in the genome," said MIT assistant professor Feng Zheng. Zheng co-senior authored the Cas9 paper, which was published in Cell.
The liver disorder that was cured was type I tyrosinemia, a disorder that prevents the breakdown of the amino acid, tyrosine. Tyrosine is used by liver cells to synthesize proteins. Someone with tryosinemia cannot break down tyrosine, which can build up and lead to cell damage.
The researchers replaced the mutated gene with a 199-nucleotide long DNA template in one out of every 250 hepatocytes, or liver cells. The cells replicated and soon overtook the mutated cells, allowing the mice to live without their tyrosinemia medication.
"We can do a one-time treatment and totally reverse the condition," said Hao Yin, a postdoctorate at the Koch Institute and one of the lead authors of the Nature Biotechnology paper.
Scientists hope that this technology leads to other single-mutation disorders such as hemophilia and Huntington's Disease, can be cured.