Many diseases seen today are the result of a defective gene in the DNA of the patient and cannot be cured using the traditional methods such as antibiotics and antiviral medication. Gene therapy is based on the concept that genetic disorders and acquired diseases can be treated by replacing abnormal or absent genes or by modifying their functions. Inherited disorders such as cystic fibrosis and hemophilia, as well as catastrophic diseases such as cancer and AIDS, are prospective candidates for gene therapy. Although cures for these ailments would be welcome, some medical researchers suggest that the range of diseases that can be treated with gene therapy may be limited