The essential difference between gene doping and conventional doping is the fact that instead of substances such as anabolics, hormones or blood, genetic material or other substances that modify how gene expression is regulated are introduced into the body.

This genetic material, or these substances, are capable of directly influencing muscle growth, fat reduction, or the production of specific hormones in the body. As a result, gene doping might in the future complement or even replace conventional doping methods owing to its ability to turn the body into its own doping factory. This is precisely what makes gene doping so incalculably dangerous: once processes are triggered in this way, they can no longer be reversed.

Every human carries genes that predispose them to particular abilities. In terms of sporting ability, for example, some are faster than others from childhood, while others are stronger, taller or better coordinated. Genes play a very central role in these differences. The particular way in which a genotype is eventually expressed (character, predilections, physical features, etc.) also depends on environmental influences.

Genes are the foundation of sporting potential

The fact that sporting potential depends on the genetic make-up can be readily inferred from a few examples:

• The fastest sprinters are dark-skinned people.
• The best marathon runners originate from East Africa.
• In gymnastics, Asian females are at an advantage because of their stature.
• Europeans dominate in strength disciplines.

It has been scientifically demonstrated that sprinters are endowed with muscles that contract especially fast but also fatigue quickly. In contrast, the muscles of endurance runners contract more slowly but can work much longer. These differences, too, are attributable to the genes.

Medical research does not develop genetic methods with the aim of using them for gene doping in sport. The aim of gene therapy is to cure people with gene-related diseases. In fact, many diseases have genetic causes: Immunodeficiencies, muscle-wasting disorders and type 1 diabetes are just a few examples. The idea of gene therapy is to treat such diseases at the genetic level by replacing defective genes with copies of healthy genes.

For ethical reasons, in most countries, gene therapy is restricted to body cells (somatic gene therapy). Gene therapy on sperm and egg cells (germ line therapy) is prohibited because any genetic modification of these cells would be passed on to the offspring. Gene therapy is currently not yet a standard medical procedure.

Gene doping can be accomplished in different ways. The current Prohibited List summarizes the following prohibited methods, with the potential to increase performance:

1. The use of nucleic acids or nucleic acid analogues that may alter genome sequences and/or alter gene expression by any mechanism. This includes but is not limited to gene editing, gene silencing and gene transfer technologies.
2. The use of normal or genetically modified cells.

Gene doping by the transfer of genes

Genes cannot simply be filled into a syringe like anabolics or EPO. To transfer genes from outside into the human organism, a kind of ferry is needed. This role is played by genetically manipulated viruses. These viruses are either injected directly into the athlete's bloodstream, or cells (e.g. bone marrow cells responsible for blood cell formation) are removed from the athlete, brought into contact with the viruses in the laboratory, and then re-inserted into the athlete's body.

Viruses transport sporting genes

Viruses are not living organisms: They consist only of an envelope and the enclosed genetic material. They cannot procreate by themselves, but they are clever. They utilise special tracking mechanisms to find their targets in the infected organism, e.g. blood cells or muscle cells. When contact is made, they introduce their own genetic substance into the victim cell. The viral genetic substance then re-programs the victim cell. From now on, the victim cell executes the instructions of the virus. If viruses are genetically modified to carry a sporting gene instead of their original disease-causing genes, they will not make the victim ill but strong, fatigue-resistant or fast.

It is also possible to modulate the expression of genes from outside. To modulate gene expression means to switch the body's natural genes on or off, or to boost or inhibit their activity. This can be achieved in two ways:

• By using small genetic elements;
• By the action of drugs.

Both of these methods have in common that – unlike the method of gene transfer – no foreign genes are inserted into the athlete's genome.

The risks of gene doping are many and varied!

Manufacturing risk: If one of the gene therapy methods currently under development is already being used illegally for doping then, having been manufactured in some obscure laboratory, the genetic material carries enormous risks.

The gene ferry: In gene therapy, viruses are used as gene ferries. These viruses are modified before administration to make them non-infectious. Nevertheless, even inactivated viruses still retain a small residual potential to cause disease.

The setting: Because the illegal manufacture of substances for gene transfer escapes public regulation and monitoring, there is a risk that incompletely inactivated viruses, contaminated products or infected instruments are used. Additionally, there is a risk that medical supervision during treatment is inadequate, or even that unauthorised, dangerous experiments on humans might be carried out.

Transfer risk: Even correctly inactivated viruses remain foreign bodies in the patient's organism and are therefore susceptible to attack by the immune system. The symptoms caused by this immune defence are similar to those of influenza. More serious problems arise if the immune system rejects the proteins produced by the inserted genes. This leads to allergic reactions including, in the worst case, fatal allergic shock.

Genetic risk: When a therapeutic gene is administered to a patient, it is not possible to control at which location it is inserted into the patient's genetic substance. Depending on the specific instance, this may have grave consequences. It is possible that an interaction between adjacent gene sections and the newly inserted gene produces an adverse or unknown effect. Not all of these possible interactions in gene therapy are known yet, and still fewer have been scientifically investigated.

At the current state of knowledge, alterations of the genetic substance by gene doping cannot be fully reversed. While many adverse effects of conventional doping subside when administration of the substance is discontinued, the effects of gene doping, including its adverse effects, are sustained and durable.

Although at present, no well-founded statement can yet be made about the feared side effects of gene doping, the following scenarios are conceivable: A growth factor, such as IGF-1, promotes the growth of muscle cells but might also stimulate the growth of tumour cells. As a result, a single pre-cancerous cell that would under normal circumstances be eliminated by the body's own control mechanisms might quickly grow into a tumour – or a cancerous disease such as leukaemia.

The detection of gene doping is particularly difficult because the product of the inserted gene cannot be distinguished from the product of the native gene. The most convenient way would be to detect the inserted gene directly in a tissue sample. A small piece of muscle would be removed from the athlete and tested for the presence of foreign DNA. However, the removal of tissue is a serious intervention for an athlete and not provided for by the World Anti-Doping Code. As a result, tissue sampling is not feasible as a standard method to detect gene doping.