While their immune systems were far from normal, PEG-ADA allows some semblance of a normal life and a much-increased life span. .

             The first patient to undergo federally approved gene therapy was a young girl named Ashanti DeSilva, in 1990. Ashanti's success immediately sparked a torrent of gene therapy investment and research. .

             There are two main types of gene therapy. There is somatic gene therapy, which encompasses all of the cells of the body excluding sperm and egg cells. The second type is germline gene therapy. The difference between the two is that changes made in somatic gene therapy are not passed on to offspring, whereas in germline gene therapy the changes are passed onto the next generation. Not much research is being done in germline gene therapy because of technical and ethical reasons.

             The first step of gene therapy is to find the location of the problem gene or genes. DNA probes are used to find the problem DNA. "The technique relies upon the fact that complimentary pieces of DNA stick together."5 The Human Genome Project is helping to piece together the location of all of the human genome.

             The U.S. Human Genome Project began officially in 1990 as a $3-billion, 15-year program to find the estimated 80,000 human genes and determine the sequence of the 3 billion DNA building blocks that underlie all of human biology and its diversity. The early phase of the Human Genome Project was characterized by efforts to create the biological, instrumentation, and computing resources necessary for efficient production-scale DNA sequencing. The first 5-year plan was revised in 1993 due to remarkable technological progress, and the second plan projected goals through 1998. Observers have predicted that the 21st century will be the "biology century." The analytical power arising from the reference DNA sequences of several entire genomes and other genomic resources is anticipated to help jump-start the new millennium.