Genetic engineering is used in humans to attempt to cure diseases; in animals to provide a larger and healthier food supply, to produce drugs, and to develop organs suitable for transplantation into humans; and in plants to make them disease- and pest-resistant, to increase their yields, improve taste, and prolong shelf life. Recent developments on the human front include the use of RNA interference (RNAi), which uses small nuclear RNAs to mask sites of abnormal splicing on genes and thus prevent translation of incorrect gene sequences; the use of lentivirus vectors to correct defective genes; and the use of adenovirus transgenes that are stable over time (1:24).
HuntingtonÆs disease is an autosomal dominant disease, and until now, efforts at genetic engineering in these patients has been directed at decreasing expression of the abnormal gene (1:24). With the new RNAi technology, an animal model in which small interfering RNA (siRNA) is tailored to a specific gene sequence that hybridizes to the complementary DNA, inhibiting its translation. The siRNA acts by binding a protein complex which targets mRNA to degrade, preventing it from making its aberrant protein and so preventing disease. It is hoped that the process can be applied to human diseases, not only to prevent them in patients with diseases such as HuntingtonÆs which develop in adulthood, but also to treat the disease in patients in whom it has already developed.
Thalassemia, a form of anemia caused by defective hemoglobin production, is being treated using gene splicing technology (1:24). In the disease, incorrect gene splicing results in a hemoglobin deficit, and in the new treatment, the defective RNA sequences are masked with U7 snRNA which has a complementary site for the defective splicing site on the pre-mRNA, a small molecule of nuclear RNA which normally processes mRNA for histones. The splicing is done using lentivirus as a vector. Since the only cu...