Gene therapy, why?

Genetic disorders can be cured by inserting genetic material into the DNA. Theoretically, this offers many possibilities: hereditary disorders could, for example, be treated by repairing a disease gene or by adding a healthy version to this gene. There are various treatment methods. This depends on the condition. Gene transfer can take place outside or inside the body, in short: a versatility within gene therapy!

What is gene therapy?

Gene therapy is the introduction of genetic material into our body cells for the purpose of medical treatment. In hereditary disorders, this genetic material can serve to switch off a gene that causes a disease by adding a ‘healthy’ gene. Gene therapy can also be used to add extra genes that can contribute to the cure of complex conditions such as cancer and cardiovascular disease

Treatment methods

Depending on the condition, treatment can be carried out by gene transfer outside the body (ex vivo) or within the body (in vivo).

Ex vivo

With the ex vivo method, the cells to be treated are first removed from the patient’s body. These could, for example, be cells from the bone marrow, which are aspirated from a patient’s bone with a needle. Blood cells can be obtained from blood. Cells can also be extracted from a piece of skin or liver that has been surgically removed (biopsy). These cells are then provided with the correct genes in the laboratory and then returned to the patient. Not all conditions can be treated with this method, because not all types of body cells are suitable for it. Examples of conditions that may be treated with this method:

  • Conditions that have their origin in the blood or blood cells
  • Some metabolic diseases

Advantages:

  • the conditions under which gene transfer takes place in the laboratory can be easily controlled. This means there is a greater chance of successful gene transfer.
  • The cells that have the new gene can be selected and cultured, resulting in a larger number of cells that all carry the therapeutic gene.

Disadvantage:

  • A disadvantage is that the treatment does involve surgery, which is painful for the patient. Moreover, restored treated cells in the patient do not always work.

 

In vivo

With in vivo treatment, the cells in the patient’s body are treated on site. For example, the gene is packaged in a virus, after which it is injected into the patient. This usually happens in the bloodstream, but can sometimes also be in the muscles. The virus then delivers the gene to the appropriate tissue or organ. If the lungs are the target organ of the treatment, an aerosol containing the virus can also be used. By inhaling this mist, the virus then enters the lungs. Examples of conditions that may be treated with this method:

  • Cystic fibrosis
  • Cancer
  • Diabetes
  • Haemophilia

Disadvantage:
The vector must be carefully targeted at the target organ to avoid gene transfer into the wrong tissues. Research shows that this is often very difficult. It often proves difficult to deliver the gene to enough cells in the body to treat a condition. A lot of research is being done to solve these problems.

Gene therapy for (hereditary) disorders

Gene therapy was initially conceived as a new therapy for hereditary disorders. In principle, gene therapy could be developed for all hereditary disorders. However, for some conditions this is easier than for others. This depends on genetic factors, and the physical characteristics of the condition.
Hereditary disorders can be caused by one gene or by multiple genes. In addition, they can be inherited recessively or dominantly.
Conditions that are caused by one gene (monogenic conditions) are in principle a relatively easier target for gene therapy than conditions for which multiple genes are responsible (multigenic conditions). After all, for monogenic disorders, only one gene needs to be ‘corrected’.
Multigenic disorders, on the other hand, are more difficult to treat, because several genes need to be ‘corrected’. Moreover, these disorders can be caused by different gene combinations, for example by six out of a group of ten. In such a case, the condition is caused by six genes in each patient, but which six (out of ten) genes differ per patient (or family). This entails several technical difficulties. Another factor that must be taken into account is the manner in which a condition is inherited. A recessive condition is easier to treat than a dominant condition. This is because it is technically easier to add a therapeutic gene than to repair the disease gene. A recessive disease gene does not necessarily need to be repaired; you can also add an extra healthy gene. The healthy gene dominates the disease gene, and the patient is cured. However,
in the case of dominantly inherited monogenic disorders, it is not possible to simply add an additional healthy gene; the disease gene will then still predominate and the patient will remain ill. In this case, a disease gene really needs to be repaired. Because this is technically more difficult than adding an extra gene, it will therefore take longer before dominant disorders can also be treated with gene therapy.
From the above it can be deduced that the conditions that are easiest to treat with gene therapy are the monogenic recessive disorders. The first available gene therapies will therefore be for this type of condition. It is expected that in the future therapies will also become available for dominant and multigenic disorders, but in the longer term.

Somatic gene therapy:

Somatic gene therapy only intervenes in the cells of the body itself, but not in the sex cells. (soma= body) This means that the effects of intervention in the DNA are only limited to the treated individual itself, and have no effect on the offspring.

Germline gene therapy:

Germline gene therapy involves interfering with an individual’s germ cells with the aim of making changes in the offspring. There are many ethical objections to this form of gene therapy.

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