Genetic Testing and Screening

g3Genetics, a discipline of biology, is the science of heredity and variation in living organisms. The fact that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding. However, the modern science of genetics, which seeks to understand the process of inheritance, only began with the work of Gregor Mendel in the mid-nineteenth century.

Genetic testing is one of the important techniques of medical science for detecting alterations in the genes and chromosomes of an individual. It helps in diagnosing genetic disorders, predicting the risks of disease occurrence and also in identifying carriers of genetic disorders.

Genetic testing or screening is a procedure for determining any changes in the genes, proteins and chromosomes. There are about 20,000 – 25,000 genes in a human genome. Genetic services are conducted to diagnose any abnormalities in the genomic content of an individual that are responsible for causing genetic disorders. For more info about genetic testing and screening please visit at  Gps.wustl.edu .

 

Benefiets of Pre-implantation Genetics Diagnosis

g2Pre-implantation genetics diagnosis (PGD) is a technique aimed at eliminating embryos created through in vitro fertilization (IVF), which have abnormal chromosomes or carrying serious genetic disease before pregnancy is established. Preimplantation genetic diagnosis (PGD) refers specifically to when one or both genetic parents has a known genetic abnormality and testing is performed on an embryo to determine if it also carries a genetic abnormality. These structural or numerical defects in the embryo can be seen more often in older pregnant women, especially those over 35. This situation may result in infertility because it reduces the chance of implantation and also causes unwanted miscarriages. As a matter of fact, 40 out of 100 pregnancies in women aged 39 and over will result in problems related to structural or numerical chromosomal defects. In contrast, preimplantation genetic screening (PGS) refers to techniques where embryos from presumed chromosomally normal genetic

parents are screened for aneuploidy.

Because only unaffected embryos are transferred to the uterus for implantation, preimplantation genetic testing provides an alternative to current post conception diagnostic procedures, which are frequently followed by the difficult decision of pregnancy termination if results are unfavorable. PGD and PGS are presently the only options available for avoiding a high risk of having a child affected with a genetic disease prior to implantation. It is an attractive means of preventing heritable genetic disease, thereby eliminating the dilemma of pregnancy termination following unfavorable prenatal diagnosis.

Indications for Preimplantation Genetic Screening

Most early pregnancy losses can be attributed to aneuploidy. Because only chromosomally normal embryos are transferred into the uterus, the risk of first and second trimester loss is markedly reduced. At present, no specific list of indications for preimplantation genetic screening (PGS) is available. For couples undergoing IVF, preimplantation genetic diagnosis may be recommended when:

1. One or both partners has a history of heritable genetic disorders.
2. One or both partners is a carrier of a chromosomal abnormality.
3. The mother is of advanced maternal age.
4. The mother has a history of recurrent miscarriages.
5. Couple had repeated IVF failures.
6. Male partner is facing problem of severe male factor infertility.

Thousands of clinical preimplantation genetic diagnosis cycles have been performed worldwide, resulting in the birth of hundreds of healthy babies.

The following are considered benefits or advantages of PGD:

The procedure is performed before implantation thus reducing the need for amniocentesis later in pregnancy.
The procedure is performed before implantation thus allowing the couple to decide if they wish to continue with the pregnancy.
The procedure enables couples to pursue biological children who might not have done so otherwise.
The procedure may help reduce the costs normally associated with birth defects.

In addition, hundreds of infants have been born following PGD/PGS worldwide. To date, there are no reports of increased fetal malformation rates or other identifiable
problems.

The main reason for opting this PGD procedure is that the risk of miscarriage during a normal pregnancy drops from 23 to 9 percent, the probability of the embryo
attaching to the womb nearly doubles, the chances of a clinical pregnancy and going home with a baby increase and the rate of multiple pregnancy decreases.

How is a PGD procedure performed?

Preimplantation genetic diagnosis (PGD) is a screening test used to determine if genetic or chromosomal disorders are present in embryos produced through in vitro
fertilization (IVF). Following are the steps involved in performing PGD procedure.

1. The patient’s suitability for PGD is evaluated by a doctor who specializes in the related disease.
2. Next, the couple is prepared for the IVF procedure.
3. The egg taken from the mother is fertilized with the father’s sperm in a laboratory environment.
4. Embryologists extract one or two blastomeric cells from the removed embryos via a biopsy.
5. Cells extracted via a biopsy are subjected to a special dyeing technique (FISH), which allows chromosomes to be examined under a microscope, following a
fixation process.
6. Embryos with structural or quantitative chromosomal defects are selected and removed. The healthy embryos are then transferred into the mother’s womb.

Genetic Disease

Genetic codeA genetic disease or disorder is any disease that is caused by an abnormality in an individual’s genome. The abnormality can range from minuscule to major — from a discrete mutation in a single base in the DNA of a single gene to a gross chromosome abnormality involving the addition or subtraction of an entire chromosome or set of chromosomes.

Why do we have genes that cause genetic disorders?

Many genes are named for the disorders to which they have been linked. This can be very confusing. For example, the gene associated with hereditary hemochromatosis is called the “hemochromatosis gene.” This name implies that the gene exists for the sole purpose of causing disease, which of course is not the case. The normal function of a gene is to encode a protein, not cause illness. Disease occurs when genes are unable to work properly. The hemochromatosis gene actually codes for a membrane protein that works with other proteins to regulate iron absorption in cells. Like other single-gene disorders, hemochromatosis occurs when a gene is mutated in a way that prevents it from encoding a normal, functional protein product. See hereditary hemochromatosis disorder and gene profiles for more information about this condition.

People who have one recessive gene for a disease are called carriers, and they don’t usually have the disease because they have a normal gene of that pair that can do the job. When two carriers have a child together, however, the child has a 1 in 4 (25%) chance of getting the disease gene from both parents, which results in the child having the disease. Cystic fibrosis (a lung disease), sickle cell anemia (a blood disease), and Tay-Sachs disease (which causes nervous system problems) are caused by recessive disease genes from both parents coming together in a child.

Genetic diseases can be inherited and are mutations in the germ cells of the body—the cells involved in passing genetic information from parents to offspring. Genetic diseases can also result from changes in DNA in somatic cells, or cells in the body that are not germ cells.

Some genetic diseases are called Mendelian disorders—they are caused by mutations that occur in the DNA sequence of a single gene. These are usually rare diseases; some examples are Huntington’s disease and cystic fibrosis. Many genetic diseases are multifactorial—they are caused by mutations in several genes compounded by environmental factors. Some examples of these are heart disease, cancer, and diabetes.

Children and adults with a rare genetic disease have multiple needs to address: health concerns, primarily, but others as well. As a service to the global Jewish community, Mazornet.com is committed to gathering and compiling data about Jewish genetic disorders. More importantly, Mazornet.com’s mission is to serve as the ultimate information resource by surfacing areas of assistance online and in the real world. It is not Mazornet.com’s intent to choose resources, but rather to make support information and resources of any kind available to the people and to the families afflicted by these diseases.