What is done to replace a defective gene with a working copy of the same gene in a patient?

Gene therapy is the process of altering defective genes in
a person with modified genes. This is presently possible to do using two methods. One is
called Germ Line Gene Therapy. This involves modification of genes in the germ cells
which are the eggs and the sperms. This can only be done in children yet to be born and
not those who already have been. The benefits of this kind of genetic modifications
would be carried over generations as the person
reproduces.

The other method is called Somatic Gene Therapy
where the altered genes are transferred into the somatic cells of patients. This therapy
affects only the person who is being treated and is not passed on to future
generations.