What is Gene Therapy?

Gene therapy is the use of genetic material- DNA or RNA- as a medicine. Classical gene therapy involves the introduction of functional genes, in the form of DNA, to replace mutated genes. This approach has been used to successfully treat a number of diseases including X-linked SCID, ADA-SCID, haemophilia B, lipoproteinlipase deficiency and Leber’s congenital amaurosis with intensive research on-going for other inherited diseases. More recently scientists are looking at using gene technology to repair rather than replace mutated genes, silence overactive genes and to also provide our immune cells with the tools they need to recognise and kill cancer cells and infections.


Discoveries in the 1960’s of enzymes which could be used to cut and paste DNA sequences together in test-tubes signified major advances in the field of genetic engineering and gene therapy. Early experiments showed that delivering engineered human genes into cells provided the instructions cells needed to make a functional protein. In 1970 Stanfield Rogers proposed the use of “good” DNA to replace defective DNA as a treatment for inherited disease.

The first approved human gene therapy attempt took place in 1990 on 4 year old Ashanti DeSilva who had ADA-SCID -an inherited disease that prevents the normal development of the immune system. Ashanti DeSilva showed real improvement no longer needing to be kept in relative isolation and able to attend school without developing any more infections than her classmates or siblings did. This early promise led to an increase in the number of gene therapy trials taking place in the 1990’s for a variety of different inherited diseases.

Despite the promise the 1990’s saw a decade of unmet potential in the gene therapy field mainly due to the inefficiency of delivering vectors. In 1999 a US gene therapy trial led to the unfortunate death of 18 year old Jesse Gelsinger who suffered from ornithine transcarbamylase deficiency -an inherited liver disease in which ammonia from the breakdown of proteins in the body is not removed. Jesse Gelsinger’s death was an awakening to all those in the gene therapy field and led to stricter safeguards to protect participants involved in medical research. Carefully drafted safety regulations focussed on ensuring scientifically robust clinical trial design and execution has prevented any repeats of the shortcomings seen in the 1999 trial.

The new millennia provided fresh hope and optimism to the field of gene therapy with rapid advances and patients showing clear improvements in their conditions in gene therapy trials. Patients have been successfully treated for a number of diseases including X-linked SCID, ADA-SCID, haemophilia B, lipoproteinlipase deficiency and Leber’s congenital amaurosis. In 2012 the Europeans Medicines Agency approved for the first time, the sale a gene therapy drug Glybera -a gene therapy treatment for lipoproteinlipase deficiency.

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