This is an area of active research, and there are many issues to solve. A technology that distributes a gene editor throughout the body is called a delivery vector, and it is typically a modified virus.
After the patient is two years old, many large molecules do not pass through the blood brain barrier. Typically most of the treatment ends up in the liver. Viruses and the gene editor can be toxic. Combining the two previous points the correct dose for most of the body can be highly toxic to the liver. The delivery vector may support genes up to a specific size (in kilobases) which may be smaller than the gene you are trying to fit. Sometimes you don't want to target organs that the delivery vector hits. Sometimes you want to target organs that the delivery vector misses. And more.
There is rapid progress being made here and all kinds of caveats and nuance to the above.
