  The HGP will assist scientists in the identification of genes and their functions. As scientists gain knowledge about how various genes contribute to phenotype, genetic modification will become possible. Such interventions could involve knocking out a gene with a detrimental role, or inserting a gene with a beneficial role, though because of gene-gene and gene-environment interactions (as discussed in section 2.1.4.), it will be difficult to predict the effects of many such interventions. The first approved GM procedure was performed in 1990 when NIH scientists genetically modified white blood cells in Ashanti DeSilva, a four-year-old girl with adenosine deaminase deficiency (ADA). Over 1000 clinical trials have since been performed (Rasko et al. 2006, Gene Therapy Clinical Trials Worldwide Database), with studies carried out on numerous diseases, including CF, Franconi's anemia, muscular dystrophy, and hemophilia. A serious setback occurred when 18-year-old Jesse Gelsinger died in a University of Pennsylvania gene therapy trial for ornithine transcarbamylase (OTC) deficiency in 1999. Shortly after, a French research team successfully restored the immune systems of young children with severe combined immunodeficiency (SCID) through gene therapy; this success was tempered, however, when several of the children later developed leukemia as a result of the procedure. Given these problems with safety and efficacy, gene therapy trials have shifted from “single-gene” diseases to conditions like cancer, cardiovascular disease, and rheumatoid arthritis, where vector applications are more local and transient (Branca 2005).