Can we cure genetic diseases by rewriting DNA? | David R. Liu

The most important gift your mother and father ever gave you was the two sets of three billion letters of DNA that make up your genome. But like anything with three billion components, that gift is fragile. Sunlight, smoking, unhealthy eating, even spontaneous mistakes made by your cells, all cause changes to your genome. The most common kind of change in DNA

is the simple swap of one letter, or base, such as C, with a different letter, such as T, G or A. In any day, the cells in your body will collectively accumulate billions of these single-letter swaps, which are also called "point mutations." Now, most of these point mutations are harmless. But every now and then,

a point mutation disrupts an important capability in a cell or causes a cell to misbehave in harmful ways. If that mutation were inherited from your parents or occurred early enough in your development, then the result would be that many or all of your cells contain this harmful mutation. And then you would be one of hundreds of millions of people

with a genetic disease, such as sickle cell anemia or progeria or muscular dystrophy or Tay-Sachs disease. Grievous genetic diseases caused by point mutations are especially frustrating, because we often know the exact single-letter change that causes the disease and, in theory, could cure the disease. Millions suffer from sickle cell anemia because they have a single A to T point mutations

in both copies of their hemoglobin gene. And children with progeria are born with a T at a single position in their genome where you have a C, with the devastating consequence that these wonderful, bright kids age very rapidly and pass away by about age 14. Throughout the history of medicine, we have not had a way to efficiently correct point mutations