Vocabulary

Dorn Spinal Therapy

Spine Healing Therapy

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gene therapy cloning by nuclear transfer telomere DNA vaccine bioethics figure 13-10

(a) DNA adjacent to the mouse Hoxd4 gene participates in normal hindbrain development. (b) After a researcher deliberately mutates the flanking DNA, he or she can see that the Hoxd4 gene is expressed in the spinal cord but not in the hindbrain.

Hindbrain

Hindbrain figure 13-10

(a) DNA adjacent to the mouse Hoxd4 gene participates in normal hindbrain development. (b) After a researcher deliberately mutates the flanking DNA, he or she can see that the Hoxd4 gene is expressed in the spinal cord but not in the hindbrain.

Spinal cord

(a)
(b)

Spinal cord

Healthy human CFTR gene

Restriction enzyme

Q Isolate functional CFTR gene

Insert CFTR gene into non-disease-causing adenovirus virus

Gene Therapy

Genetic engineering has also allowed biologists to try to treat genetic disorders in different ways. One method is a technique called gene therapy. In gene therapy a genetic disorder is treated by introducing a gene into a patient's cells. Gene therapy works best for disorders that result from the loss of a single protein. For example, the lung disease cystic fibrosis results from the lack of a functional gene called the CFTR gene. When functional, the gene encodes a protein that helps transport ions into and out of cells in the breathing passages. Without that gene, poor ion exchange causes the symptoms of cystic fibrosis, including the buildup of sticky mucus that blocks the airways.

Figure 13-11 summarizes the steps involved in gene therapy. In step O, researchers isolate the functional gene (such as the CFTR gene). In step ©, they insert the healthy gene into a viral vector. In step ©, they introduce the recombinant virus to the patient by infecting the patient's airway by means of a nasal spray. The healthy copy of the CFTR gene temporarily produces the missing protein and improves ion exchange. The traditional treatment for cystic fibrosis involves thumping sessions—clapping on the back and chest for half-hour periods several times a day to dislodge mucus.

Cystic fibrosis research has accelerated since the discovery of the CFTR gene in 1989. In the laboratory, researchers were able to add a healthy copy of CFTR into the DNA of cystic fibrosis cells. The result was an immediate return to a normal ion transport mechanism. However, trials in the laboratory are different from trials on living humans. Apparently, the cells that express the highest levels of CFTR are deeper in the lungs than the surface cells that current forms of gene therapy can reach. Because the cells that line the airway slough off periodically, the treatment must be repeated. In addition, patients may suffer immune reactions to the treatment. Researchers hope to overcome these obstacles and to one day provide a permanent cure.

People with certain kinds of hemophilia, acquired immunodeficiency syndrome (AIDS), or some cancers are future candidates for gene therapy. Until recombinant DNAs can be inserted into the correct cells, however, and immune reactions can be prevented, gene therapy may continue to be a short-term solution.

I Infect patient's airway cells with virus carrying the healthy CFTR gene

figure 13-11

The steps in gene therapy for cystic fibrosis are summarized. The patient in the photo is receiving gene therapy for cystic fibrosis. A healthy copy of the gene responsible for cystic fibrosis is being administered through a nasal spray.

figure 13-11

The steps in gene therapy for cystic fibrosis are summarized. The patient in the photo is receiving gene therapy for cystic fibrosis. A healthy copy of the gene responsible for cystic fibrosis is being administered through a nasal spray.

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