1. INTRODUCTION

There are at least 4000 human diseases, which could be of genetic origin. Nuclear genes (one or more genes) or mitochondrial disorders or chromosomal imbalance causes some of these diseases. For example, about 5% of live born babies suffer from a significant medical disorder, most of them have a genetic component. A number of these disorders can be cured by supplementing, the target deficient cells with external drug, that replaces the product of the expression of the gene.  However, the rate of such treatment is low by using the traditional mode of treatment. But, recently, a new way of treating many of these diseases has immerged in the scientific literature, called gene therapy.  This involves, treating the genetic disease by introducing the nondefective gene into the patient, replacing or adding a new gene in order to create a more favourable phenotype.  The first successful gene treatment was reported in 1990 by Anderson, of that of the fatal genetic disease, severe combined immunodeficiency (SCID). This disease destroys much of the immune system, particularly the white blood cells (T cells) due to the absence of the enzyme adenosine deaminase. The gene responsible for the enzyme adenosine deaminase is a recessive one, preventing the formation of this enzyme. Without the enzyme, the body fails to break down chemicals produced during normal

Recent advances in molecular biology and DNA technology explained the role of any specific gene product in causing the disease. Isolation, identification of any gene followed by the determination of its DNA sequences has enriched our knowledge on how the gene functions. It is now well understood that the gene product is a type of protein. If the gene is defective, this will lead to the lack of such protein causing the disease. An international effort was launched to identify every single human gene, with a project known as the human genome project This project is expected to finish approximately in year 2005. (Hawley, and Mori 1999)                                                  

Recent advances in research on gene therapy covers curing diseases such as cystic fibrosis (Wagnerand and Gardener1997, Welsh. and Oestedgoard 1998), liver diseases (Davern and Scharschmidt 1998, Wa et al 1998) and cell anemia. It is now used in a wide range of other diseases including cancer (Dachs et al 1997, Ficazzola and Tanejn 1998), cardiovascular diseases (Snowden and Grave 1998), arthritis and neurodegenerative disorders (Kaplit et al 1998) and acquired diseases such as HIV AIDS (La Frace and Mang 1997)