Genetic Engineering can be used to treat diseases

Proteins used to treat diseases

There is a protein called Erythropoietin (EPO). EPO is a hormone-like
substance made by the kidneys. It enters the bloodstream, goes to the
bone marrow and stimulates the production of red blood cells. Red
blood cells only last about 120 days, so they must be constantly
replaced. There are many people with kidney failure for various
reasons. These people are treated with kidney dialysis, because kidney
transplants are limited.

The kidney filters out the poisons and keeps the good things. In this
case, all you can do is to filter the bad things with the dialysis
machine. Among the things that get filtered out is EPO. So, these
people with kidney failure have kidney function restored by dialysis,
but they’re not making EPO. They have severe anemia. The only way to
get around this is by massive transfusion or to treat them with EPO.

The gene coding for EPO was isolated, EPO was made by recombinant DNA
technology, and this is now widely used for people who are undergoing
kidney dialysis and also people who are being treated with cancer
chemotherapy. Many of the drugs used in chemotherapy destroy bone
marrow cells.

EPO is also the first genetically engineered drug of abuse. Athletes
found that if they take some EPO they can increase their blood cell
count. Increasing the amount of red blood cells by about 10% can give
an athlete an edge in competition. There had been great controversies
in cycling and elsewhere because of the abuse of EPO.

Article from: http://human-genetics-blog.blogspot.sg/2010/01/benefits-of-genetic-engineering.html