File Name: genetic testing and screening .zip
We all have 46 chromosomes in our cells. Chromosomes are made from DNA. Genes are short sections of DNA deoxyribonucleic acid and each chromosome contains hundreds to thousands of genes. Genes contain the information our bodies need to make chemicals called proteins. Proteins form the structure of our bodies and play an important role in the processes that keep us alive.
It is the differences in our genes that makes us all individuals. Sometimes a gene may change this is called a mutation and either cause or increase the risk of a disease or disorder. Genetic testing is a type of medical test that identifies changes in chromosomes, genes or proteins.
Genetic tests examine a person's DNA in a variety of ways. They are all designed to identify a particular gene that may cause a genetic disorder. Note : the information below is a general guide only. The arrangements, and the way tests are performed, may vary between different hospitals. Always follow the instructions given by your doctor or local hospital. Your body is made up of millions of tiny cells.
Different types of cells form the different structures of the body, including skin, muscles, nerves and also organs such as the liver and kidneys. In the centre nucleus of most cells in your body, the DNA molecule is packaged into thread-like structures called chromosomes.
You have 46 chromosomes arranged in 23 pairs. These include one pair of sex chromosomes either XX for females and XY for males. The other chromosomes that do not determine whether we are male or female are called autosomes. There are 22 pairs of autosomes numbered 1 to One chromosome from each pair comes from your mother and one from your father. A gene is the basic unit of your genetic material. It is made up of a sequence or piece of DNA and sits at a particular place on a chromosome.
So, a gene is a small section of a chromosome. Each gene controls a particular feature or has a particular function in your body. For example, dictating your eye colour or hair colour, making all the various proteins in your body, etc.
Each gene is part of a pair. One gene from each pair is inherited from your mother, the other from your father. Each chromosome carries hundreds of genes. Humans have between 20, and 25, genes altogether. The total of all your genes is called your genome. DNA stands for deoxyribonucleic acid. DNA forms your genetic material. Genes, which are made up of DNA, act as instructions to make proteins. Proteins are large, complicated molecules that play many important roles in your body.
They do most of the work in cells and are required for the structure, function and regulation of your body's tissues and organs. As our cells are multiplying all the time, our genetic information needs to stay the same. Normally, there are excellent mechanisms in place to make sure each cell gets the exact same copy of DNA, the material that makes up our genes. However, sometimes the copying mechanism makes mistakes or other problems can occur with your genetic material.
Problems and abnormalities in genes can lead to genetic diseases. Gene tests look for abnormalities in DNA taken from a person's blood, body fluids or tissues. The tests can look for large mistakes such as a gene that has a section missing or added.
Other tests look for small changes within the DNA. Other mistakes that can be found include genes that are too active, genes that are turned off, or those that are lost entirely. They are all designed to identify differences between the gene being tested and what would be considered to be a normal version of the same gene.
These look at single genes or short lengths of DNA taken from a person's blood or other body fluids for example, saliva to identify large changes, such as:. An example of a genetic disorder that is tested in this way is cystic fibrosis. However, there are limitations to genetic testing, as it is only useful if it is known that a specific genetic mutation causes a certain condition.
A mutation or error in copying the DNA results in a permanent change to the DNA which can result in a number of diseases.
For example, a specific gene mutation is known to cause Huntington's disease. It is therefore possible to test a blood sample for the presence or absence of this gene mutation. For many conditions - for example, diabetes - there may be any one of hundreds or even thousands of different possible mutations in a particular gene. This means genetic testing for those conditions is virtually impossible. These look at the features of a person's chromosomes, including their structure, number and arrangement.
Parts of a chromosme can be missing, be extra or even be moved to a different part on another chromosome. Biochemical tests look at the amounts or activities of key proteins. As genes contain the DNA code for making proteins, abnormal amounts or activities of proteins can signal genes that are not working normally. These types of tests are often used for newborn baby screening. For example, biochemical screening can detect infants who have a condition affecting one of the many essential chemical reactions in the body metabolic condition such as phenylketonuria.
The results of a genetic test can confirm or rule out a suspected genetic condition or help determine a person's chance of developing or passing on a genetic disorder. More than 2, genetic tests are currently in use, and more are being developed all the time. Newborn screening is done just after birth to identify genetic disorders that can be treated early in life.
For example, every baby in the UK is tested for cystic fibrosis as part of the heel prick test. Diagnostic testing is used to identify or rule out a specific genetic disorder if a baby or person has symptoms to suggest a certain genetic disorder for example, Down's syndrome. Carrier testing is used to identify people who carry one copy of a gene mutation a genetic change that, when present in two copies, causes a genetic disorder for example, sickle cell disease.
This type of test can be useful to provide information about a couple's risk of having a child with a genetic disorder. Before birth prenatal testing is used to detect changes in an unborn baby's genes.
This type of testing is offered during pregnancy if there is an increased risk that the baby will have a genetic or chromosomal disorder. It cannot identify all possible inherited disorders and birth defects, however. Pre-implantation genetic testing is available for couples who are at risk of having a child with a specific genetic or chromosome disorder, eg cystic fibrosis, sickle cell disease or Huntington's disease.
Egg cells are removed from the woman's ovaries and then fertilised with sperm cells outside the body. This is called in-vitro fertilisation or IVF. The eggs are fertilised with sperm cells to form embryos. The fertilised embryos develop for three days and then one or two cells are removed from each embryo. The genetic material DNA and chromosomes from the cells are tested for the known disorder in the family.
One or two of the unaffected embryos are then transferred into the mother's womb uterus. If the pregnancy is successful, the baby will not be affected by the disorder it was tested for. Predictive testing is used to detect genetic mutations associated with disorders that appear after birth, often later in life. These tests can be helpful to people who have a family member with a genetic disorder but who have no features of the disorder themselves at the time of testing for example, breast cancer associated with the BRAC1 gene.
Predictive testing can identify mutations that increase a person's risk of developing disorders with a genetic basis, such as certain types of cancer. Testing can also determine whether a person will develop a genetic disorder, such as haemochromatosis , before any signs or symptoms appear.
People in families at high risk for a genetic disease have to live with uncertainty about their future and their children's future. A genetic test result showing a known gene mutation responsible for a certain disease as not being present in a person can provide a sense of relief.
However a positive result may have a devastating effect on a person's life, especially if there is no known treatment. However for some disorders a positive result may help you to consider options to prevent the disorder. For example, women with BRAC1 are at increased risk of breast cancer and may decide to have surgery to remove their breasts mastectomy or to take a medicine called tamoxifen to reduce the risk.
See the leaflet on Breast Cancer for more information. Therefore before having predictive testing it is essential for a specialist to carefully discuss with you your risks of being affected by the disorder, how the disorder would affect you and the benefits and risks of having a genetic test for the disorder. See the section on genetic counselling below. Forensic testing uses DNA sequences to identify a person for legal purposes.
Unlike the tests described above, forensic testing is not used to detect gene mutations associated with disease. This type of testing can also be used to work out the paternity of a child. Forensic testing can also be used for identifying human remains when identification is not possible by other means - for example, after a natural disaster such as a fire or tsunami. Genetic testing usually involves taking a sample of blood or tissue.
In adults and children this usually involves taking a blood sample from a vein. Some genetic tests can be done from samples of saliva or from taking a sample swab from the inside of your mouth. In pregnancy, a sample may be taken from the baby by amniocentesis or chorionic villus sampling. In amniocentesis a sample of the liquid amniotic fluid that surrounds a baby is taken. It is done by putting a needle though the tummy abdomen into the womb uterus.
Back to test list. Approximately 1 in 16 people is a carrier of one or more of these conditions. Most carriers do not have a family history of relatives affected by the disorder and are unaware that they are carriers. The result provided will indicate whether a mutation was found, and the implication for the patient. Genetic counselling and testing of reproductive partner is recommended. Carrier for FXS Females: individual is at increased risk of having affected children. This result also has potential medical implications for the individual being tested.
Birth defects, which occur in nearly one in 20 pregnancies, range in severity from minor anatomic abnormalities to extensive genetic disorders or mental retardation. Some couples have a greater than average risk of having a child with a birth defect. Genetic screening refers to the use of specific tests to determine which members of a population are at increased risk for an inherited condition. Genetic testing, in contrast, is the use of specific tests to characterize the genetic status of an individual who is suspected to be at increased risk for an inherited disease. These terms are frequently used interchangeably.
We all have 46 chromosomes in our cells. Chromosomes are made from DNA. Genes are short sections of DNA deoxyribonucleic acid and each chromosome contains hundreds to thousands of genes. Genes contain the information our bodies need to make chemicals called proteins. Proteins form the structure of our bodies and play an important role in the processes that keep us alive. It is the differences in our genes that makes us all individuals. Sometimes a gene may change this is called a mutation and either cause or increase the risk of a disease or disorder.
Genetic testing can provide information about a person's genes and chromosomes. Available types of testing include:. Newborn screening is used just after birth to identify genetic disorders that can be treated early in life. Millions of babies are tested each year in the United States. All states currently test infants for phenylketonuria a genetic disorder that causes intellectual disability if left untreated and congenital hypothyroidism a disorder of the thyroid gland. Most states also test for other genetic disorders.
Genetic testing can also include measuring the results of genetic changes, such as RNA analysis as an output of gene expression , or through biochemical analysis to measure specific protein output. The variety of genetic tests has expanded throughout the years. Early forms of genetic testing which began in the s involved counting the number of chromosomes per cell. Deviations from the expected number of chromosomes 46 in humans could lead to a diagnosis of certain genetic conditions such as trisomy 21 Down syndrome or monosomy X Turner syndrome. Genetic testing is "the analysis of chromosomes DNA , proteins, and certain metabolites in order to detect heritable disease-related genotypes , mutations , phenotypes , or karyotypes for clinical purposes.
Read terms. This document reflects emerging clinical and scientific advances as of the date issued and is subject to change. The information should not be construed as dictating an exclusive course of treatment or procedure to be followed. ABSTRACT: Given the increasing availability and complexity of genetic testing, it is imperative that the practicing obstetrician—gynecologist or other health care provider has a firm comprehension of the benefits, limitations, and risks of offering a specific genetic test, as well as the importance of appropriate pretest and posttest counseling. The purpose of this Committee Opinion is to provide an outline of how obstetrician—gynecologists and other health care providers can best incorporate these tests into their current practices and provide appropriate pretest and posttest counseling to patients. Obstetrician—gynecologists and other health care providers should determine which tests will be offered as the standard in their practices so that similar testing strategies are made available to all patients.
application of genetic screening tests. Screening was originally proposed as a means of early disease detection in asymptomatic. individuals in.
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