Gene therapy generally involves introducing one or more genes into diseased cells of an organism in order to palliate the disease or – ideally – even to cure it. Genes are the bearers of genetic information, i. e. they contain the blueprints for the proteins. If a gene fails, for instance due to an error in the genetic code of the DNA, the cell is no longer able to form this protein, or at best to form a defective version that is unable to perform the natural function. Such a deficiency may directly result in disorders such as heamophilia or Huntington’s disease. Diseases caused by the failure of a single gene are known as monogenetic diseases. If more than one gene is responsible for the deficiency, the correct term is “multigenetic diseases”. Gene therapy targets the origin of these diseases, the deficiency in the genetic material. Treatment involves introducing a faultless copy of the defective gene into the diseased cells, enabling them to synthesise the missing protein – at least to a certain degree.