Infectious diseases genetic testing

Подтема 3. Генетическая диагностика наследственных и инфекционных заболеваний

1. Gene Diagnostics is the testing of DNA for mutations that could lead to a number of diseases and or genetic disorders. A very accurate diagnosis can be made on a wide array of genetic disorders by doing a genetic test or screening. A genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions. Genetic testing (also called DNA-based tests) is among the newest and most sophisticated of techniques used to test for genetic disorders which involves direct examination of the DNA molecule itself. Other genetic tests include biochemical tests for such gene products as enzymes and other proteins and for microscopic examination of stained or fluorescent chromosomes. Genetic tests are used for several reasons, including:

- identifying unaffected individuals who carry one copy of a gene for a disease that requires two copies for the disease to be expressed, these are some examples:

- preimplantation genetic diagnosis (see the side bar, Screening Embryos for Disease)

- prenatal diagnostic testing [e.g. phenylketonuria (PKU) - an autosomal recessive metabolic genetic disorder characterized by a mutation in the gene for the hepatic enzyme phenylalanine hydroxylase (PAH), rendering it nonfunctional]

- newborn screening

- genealogical DNA test (for genetic genealogy purposes)

- presymptomatic testing for predicting adult-onset disorders such as Huntington's disease

- presymptomatic testing for estimating the risk of developing adult-onset cancers and Alzheimer's disease

- confirmational diagnosis of a symptomatic individual

- forensic/identity testing

When we hear the term "infectious disease," we usually think of something that can infect us and cause a disease process to begin. That "something" can be a bacteria, virus, parasite, or fungus obtained from many different sources (other infected individuals, poor hygiene, transfusion with infected blood, shared needles between drug users, etc.). Disease-causing bacteria and viruses are known as infectious agents, and some of them can be quickly identified by using genetic testing techniques; however, common infectious agents, such as certain bacteria and viruses, are much less expensive to identify using standard laboratory methods that don't involve genetic testing techniques.

Bacteria are one-celled organisms that contain their own DNA and in some cases can cause serious disease. Even those bacteria that harmlessly live inside our bodies and are involved in beneficial chemical processes can become mutated under unusual conditions and cause us to be very sick. By isolating the DNA from bacteria, breaking it into small pieces, and amplifying them, the bacteria can be identified very quickly. Some of the bacteria that can be quickly identified using these genetic testing techniques include: Chlamydia trachomitis, which is an organism that causes the sexually-transmitted disease chlamydia; Neisseria gonorrhea, which causes gonorrhea, Borrelia burgdorferi which causes Lyme Disease, Legionella pneumophilia which causes Legionnaire's disease, Mycoplasma pneumoniae which leads to "walking pneumonia," Mycopbacterium tuberculosis which can cause tuberculosis, and Bordetella pertussis which causes whooping cough. Specimens that might contain these bacteria include urine, blood, sputum, cerebrospinal fluid, and others.

Viruses are unusual organisms that sometimes insert their DNA into a host's genome. The viral RNA or DNA utilizes the host's cells to produce proteins and make more viruses. Viruses such as hepatitis C virus (HCV) and human immunodeficiency virus (HIV) are examples of RNA viruses.

Other disease-causing viruses that contain DNA instead of RNA include Herpes simplex virus, cytomegalovirus, Epstein-Barr virus, parvovirus, and varicella-zoster viruses. All of these viruses can be identified by first removing the suspected viral DNA or RNA from a patient specimen and then using it to provide a "fingerprint" of the suspected virus. Specimens usually include blood, cerebrospinal fluid, sputum, other body fluids, amniotic fluid, tissue, or bone marrow. Much of the testing on donor blood that will be used in a blood transfusion utilizes genetic testing to inspect the blood for viral contamination.

Determining how many copies of a virus' RNA are present in an individual's blood is another use of infectious disease genetic testing techniques. The number of copies present is typically referred to as the "viral load" or "viral burden." This testing is usually done after a drug therapy is initiated to assess whether it is working to remove or decrease the viral RNA load. The most common viral load tests are for HCV or HIV, and the tests require a sample of blood.

A parasite is a complex multi-cellular organism. Parasites usually infect an individual through the saliva of a biting insect, such as a mosquito, or through infected material. An example of a parasite that can be identified using genetic tests is Toxoplasma gondii, which can cause encephalitis or congenital infections that lead to severe damage of a fetus (fetal toxoplasmosis).

Дата добавления: 2013-12-12