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There are over 1000 of different diseases that are known to be hereditary. Some occur with the small prevalence in population, and some are more prevalent. The primary task of the research in human molecular genetics is to determine what kind of gene damage is made, and how do they represent the symptoms of the particular genetic disorder.

One of the approaches to the study of hereditary disease is to isolate the defective and normal gene, which allows the comparative analysis of them. In case of the discovery of altered gene that causes the disease, the diagnostic tests can be developed for its precise detection by using molecular biotechnology. Using those tests, it is possible to determine, for example, in the very beginning of the pregnancy whether the child will be born with "healthy" or "sick" genome. In addition to diagnostics, knowledge about changes of DNA can lead to a better understanding of the molecular basis of certain diseases, and therefore to find the best solutions for its treatment.

Cloning of a Normal Gene
Cloning of a normal gene, which is responsible for the altered form the disease can be used to treat the disease, and the level of genetics. Therefore, these procedures are considered under the name “Gene Therapy”. Gene therapy can be performed on cells in culture, which are then returned in patients body (ex vivo gene therapy), or the normal gene is directly inserted into the patients body.

Ex Vivo Gene Therapy

In ex vivo gene therapy, cells obtained from the patient are used, and their genetic defect is corrected by inserting a normal gene. The next step is , the selection of cells with desired characteristics, and such cells are grown in culture in order to be returned to the patient. The advantage of this kind of gene therapy is that it is based on autologous cells which are not rejected by the patient's immune system. However, this method is extremely expensive and it requires a lot of time because every step needs to be done for each patient individually. Therefore, it scientists are working on isolating the cells which would be universal donors, in fact, the cells which would not be rejected by any human organism. One of the strategies for ex vivo gene therapy is based on using smooth muscle cells found in blood vessels. It is possible to return these cells back into the body after small intentionally caused surgical injury on small blood vessels. During the wound healing process the genetically changed cells become part of the tissue.

The advantage of this method is that genetically modified cells are in the contact with circulatory system, and they can secrete desired protein directly into the bloodstream. In addition to genetically determined diseases, there is a possibility for genetic therapy to be used in the treatment of certain types of malignancies.

In Vivo Gene Therapy

For in vivo gene therapy, the methods for inserting healthy genes directly into the patient's tissue with the help of pure plasmid DNA or with the help of some viruses, such as genetically engineered adenovirus or herpes simplex virus. No matter what kind of vector used in gene therapy in vivo, it is necessary to take into account the fact that the vectors are tissue-specific tissue-specific. It is achievable by using viruses which would selectively attack certain tissues, or the gene inserted would be under control of expression signals which can be recognized in target tissues only.

The herpes simplex virus, which infects just nervous cells is the appropriate choice, and that in the near future it could be used to treat patients with neurological disorders.

By using the animal systems, scientists had shown that this type oftherapy is achievable. Numerous experiments have shown that it is possible to insert the plasmid with the cloned gene for the protein dystrophin in the muscle cells of laboratory animals where this gene expressed successfully. That way, the possibility for treatment of Duchene muscle dystrophy is opened.

Yet perhaps, the greatest progress is made in efforts for therapy of malignant brain tumors with the help of retroviral vector system. In tests with experimental animals has been shown that the vector enters only the malignant brain cells, which are then destroyed, and the entire treatment has no effect on healthy brain cells. Because of the great success of this method, the permissions for clinical trials on volunteers with brain tumor are already obtained.

Bearing in mind the contribution of molecular biotechnology to medicine Dr. Francis Collins, director of U.S. National Institute of Human Genome Research gave a prediction of the development for next 40 years. He divided the postgenom era in four phases:

Phase I (5 years):

(a) Rapid acceleration of the development of molecular diagnostic tests,
(b) Identification of molecular subtypes of major human diseases

Phase II (10 years):

(a) Growing number of therapies based on targeted action on the certain molecules in the body,
(b) Defining of pharmacogenomic markers for following patient's response to drugs
© Development of new probes for the visualization of monitoring of bodily functions,
(d) Development of tests for predicting more than 20 genetic disorders that can lead to disease.

Phase III (15 to 20 years):

(a) Testing of different populations development of a database of genotypes,
(b) Design of drugs for diabetes, for high blood pressure, of different types of cancer and other diseases,
© General type of therapy division into subtypes, according to diversity of genotypes,
(d) Full replacement of regenerative medicine (getting oneself tissues out of somatic cells,
(e) Gene replacement in utero and adults.

Phase IV (30 years):

(a) The genes responsible for aging will be determined and will be used in clinics to prolong human life,
(b) Comprehensive health care based on genomics.