Monday, August 2, 2010

GENETIC TESTING

POSTED BY GROUP 6 :
Kenneth Photlokwe (2160800061), PriscillaKgosintwa(2160800073), Bonny Masupane(2160800014) & Letitia Stephen(2160800018)

GENETIC TESTING

Genetic testing are tests on blood and other tissue to find genetic disorders. Genetic testing is also known as DNA- based test and is the latest and most sophisticated techniques used to test for genetic disorders. This technique involves direct examination of the DNA molecule itself while other genetic tests include biochemical tests for the particular gene product such as enzymes and other proteins and for microscopic examinations of stained or fluorescent chromosomes. Genetic testing involves analyzing a person’s DNA, RNA, chromosomes, proteins or metabolites obtained from a sample of blood, hair, skin or other tissue in order to confirm a diagnosis of a genetic condition, identify carriers of a genetic gene condition, or to determine person’s predisposition to a particular health condition.

There are different methods and laboratory techniques that are used in genetic testing and the method to be used to perform the test on the gene depends largely on the goal of the test. Different tests and different techniques are applied to find different gene defects and those different methods are molecular genetic testing, cytogenic testing, biochemical tests and simple blood tests. For instance; Molecular genetic testing refers to techniques that directly analyze specific DNA or RNA sequences, cytogenic testing is used to diagnose chromosomal abnormalities, such as the presence of an extra chromosome or deletion of a chromosomal segment, biochemical tests are used to detect characteristic biochemical markers of a specific genetic condition like galactosemia. Simple blood test, which is also called a hematologic test, is used to diagnose sickle cell disease.

Carrier identification or screening, pre implantation genetic diagnosis, pre natal diagnosis, new born screening and testing for late onset disorders are types of the different genetic testing done today. Another test is forensic or identity testing, commonly known as DNA fingerprinting, which is often used to identify genetic information and discover if it belongs to a specific somebody. In law enforcement agencies, it’s used in solving crimes and is also used in paternity cases.

HOW GENETIC TESTING IS DONE

Before a person has a genetic test, it is important that he or she understands the testing procedure, the benefits and limitations of the test, and the possible consequences of the test results. The process of educating a person about the test and obtaining permission is called informed consent. Genetic testing is often done as part of a genetic consultation and once a person decides to proceed with genetic testing, a medical geneticist, primary care doctor, specialist, or nurse practitioner can order the test. Genetic tests are performed on a sample of blood, hair, skin, amniotic fluid (the fluid that surrounds a fetus during pregnancy), or other tissue. For example, a procedure called a buccal smear (the painless removal of a sample of cells from the lining of the mouth for study) uses a small brush or cotton swab to collect a sample of cells from the inside surface of the cheek.

The sample is sent to a laboratory where technicians look for specific changes in chromosomes, DNA, or proteins, depending on the suspected disorder. The laboratory reports the results in writing to a person’s doctor or genetic counselor.

Newborn screening tests are done on a small blood sample, which is taken by pricking the baby’s heel with a lancet. For this test, a parent will only receive the result if it is positive then additional testing is needed to determine whether the baby has a genetic disorder.

The results of genetic tests are not always straightforward, which often makes them challenging to interpret and explain. When interpreting test results, healthcare professionals consider a person’s medical history, family history, and the type of genetic test that was done.

A positive test result means that the laboratory found a change in a particular gene, chromosome, or protein of interest. Depending on the purpose of the test, this result may confirm a diagnosis, indicate that a person is a carrier of a particular genetic mutation, identify an increased risk of developing a disease in the future, or suggest a need for further testing. A negative test result means that the laboratory did not find a dangerous copy of the gene, chromosome, or protein under consideration. This result can indicate that a person is not affected by a particular disorder, is not a carrier of a specific genetic mutation, or does not have an increased risk of developing a certain disease. It is possible, however, that the test missed a disease-causing genetic alteration because many tests cannot detect all genetic changes that can cause a particular disorder. Further testing may be required to confirm a negative result.

USES OF GENETIC TESTING

Genetic tests can be used to look for possible predisposition to diseases as well as to confirm a suspected mutation in an individual or family.

Ø New born screening

Infants have blood samples tested for abnormal or missing gene products, some tests look for abnormal arrangements of the chemical bases in the gene itself and identify the genetic disorders that can be treated early in life.eg phenylketonuria (a genetic disorder that causes mental retardation if left untreated).

Ø Carrier testing

It can be used to help couples to learn if they carry a recessive allele for inherited disorders such as sickle cell anemia and that they risk passing the disease to their children. It is also used to identify people who carry one copy of a gene mutation that when present in two couples causes a genetic disorder. This test is offered to individuals who have a family history of genetic disorder and to people in certain ethinic groups with an increased risk of specific condition.

Ø Prenatal testing

Used to detect the changes in a fetus’s genes or chromosomes before birth. It is offered during pregnancy, but it cannot identify all possible inherited disorders and birth defects.

Ø Forensic testing

Uses DNA sequencing to identify an individual for legal purposes. It is used to detect gene mutations associated with diseases. It can identify crime or catastrophe victims rule out or implicate crime suspects. It can also be used for paternity testing therefore establishing biological relationships.

Ø Predictive and presymptomatic testing

· Used to detect gene mutation associated with disorders that appear after birth. Can be helpful to individuals who have a family member with genetic disorder, but who have no features of the disorder themselves at the time of testing.

· Can identify mutations that increase a person’s risk of developing disorders with genetic basis such as certain types of cancer.

· Presymptomatic testing can determine whether a person will develop a genetic disorder such as hemochromatosis (an iron overload disorder).

Ø Pre-implantation testing / pre-implantation genetic diagnosis (PGD)

· A special technique that can reduce the risk of having a child with a particular genetic or chromosomal disorder.

· Used to detect genetic changes in embryos that were created using assisted reproductive techniques such as an in-vitro fertilization.

PROS OF GENETIC TESTING

Ø genetic testing can find out if an individual is at risk of inheriting any of the diseases that are tested for.

Ø Let parents know whether their child has a genetic disorder.

Ø A negative result can create a tremendous sense of relief and may eliminate the need for frequent checkups and tests that are routine in families with a high risk of cancer

Ø Helps one to make informed decisions more especially if the test result is positive.

CONS

- risks associated with genetic testing involve emotional, financial or social consequences of the test results.

Legal issues, such as patient privacy, use of genetic testing to determine insurance coverage, and the use of archived patient samples are a concern.

Many genetic tests cannot detect all of the variations that can cause a particular disease. For instance, with genetic testing for cystic fibrosis, most genetic testing panels only look for the more common variants, not all of those that are associated with this disease.

A positive genetic test can also lead to an increased level of anxiety and individuals may feel guilty for having potentially passed a gene alteration on to their children.

One may test positive for a gene that indicates a genetic disorder but never develop it.

Ø genetic testing is expensive, costing about $300 to $3,000, depending on the extent of testing. Many insurance plans, including Medicare, cover the cost of the testing for women at high risk, but coverage is unlikely for women not considered to be at high risk.

References

· http://www.bionetonline.org/english/content/gh_cont1.htm

· Microbiology, an introduction. Tortora, Funke and Case.(2002)7th edition. Benjamin C Cummings, Pearson education. San Francisco.

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