GENE SCREEN TECHNOLOGY

•Systematic application of testing designed to identify individuals in a given population who are at higher risk of having or developing a particular disorder of or having a gene mutation for a particular disorder.

•Newest and most sophisticated of the techniques used to test for genetic disorders.

•One of the fastest moving fields in medical science.

•Determines the risk of having or passing on a genetic disorder.

• Used to detect faulty or abnormal genes in an organism.

• Detect some genes related to an increased risk of cancer.

• Detect some genes known to cause genetic disorders.

CRITERIAS

Genetic screening should not be performed unless a number of conditions are met.

1. Condition to be screened for should be serious.

2. Diagnostic methodology should be adequate.

.

3.The condition must be sufficiently frequent to make the programme economically feasible.

4. The individual identified as at risk must have some options, preferably either effective early treatments or prenatal diagnosis.

.

TYPES OF SCREENING

There are three principle types of genetic screening

Prenatal genetic screening Carrier screening Newborn screening

PRENATAL SCREENING Also called as fetal screening Prenatal screening identifies disease

in fetus. It makes possible averting the

unwanted birth of a child with a genetic condition.

The purpose of prenatal diagnosis is to detect significant defects in fetus.There is now a variety of techniques,each of which has unique advantages and disadvantages.

Amniocentesis Amniocentesis is a surgical tap into the

uterus to obtain amniotic fluid. The amniotic fluid can be analyzed to

determine the genetic status of fetus. Initially used for the diagnosis of the

disease erythroblastosis fetalis. The procedure can be performed at 14

weeks gestation or later. It is most commonly done between 15-19 weeks.

• Currently the most common indication for genetic amniocentesis is an increased abnormalities in the fetus.

• Helpful in diagnosis of open fetal defects such as neural tube or ventral wall defects.

• Early amniocentesis is generally defined as amniocentesis less then 14 weeks of gestation which may lead to high risk of pregnancy loss.

Chorionic Villus Sampling Chorionic Villus Sampling is a

procedure for placental biopsy. It is the removal of a piece of

chorion,the outer tissue surrounding the embryo.

The tissue sample is used to analyze chromosome ,biochemical and DNA status.

Chorionic Villus Sampling for common genetic indications is performed at 10-12 weeks of gestation.

Percutaneous Umbilical Blood Sampling(PUBS) It is a fetal blood sample test that

takes measurements of fetus blood components.

These results are used to clarify other test results.

Ultra sonogram One of the most common screening procedures

during pregnancy. A transducer sends a sound wave that provides a

picture of the fetus. The procedure is used to date the

pregnancy,assess structure and position of the fetus.

Maternal serum markersalpha fetoprotein is most abundant globular serum

protein fetus. Large amounts of AFP are found in fetal blood and fetal tissues. Increased or decreased levels of AFP may indicate a variety of fetal abnormalities.

Decreased levels of unconjugated oestrol and the increased levels of human chorionic gonadotropin (HCG) are associated with fetal Down syndrome.

•Combining information from these markers provides a more accurate estimate of fetal Down syndrome risk than any one factor alone.

•This is commonly offered to patients at approximately 15-18 weeks of pregnancy.

Pre-implantation

Also called pre-implantation genetic diagnosis(PGD),is a specialized technique that can reduce the risk of having a child with a particular genetic or chromosomal disorder.

It is used to detect genetic changes in embryos that were created using assisted reproductive techniques such as in-vitro fertilization.

CARRIER SCREENING The usual purpose in identifying carriers

is to detect a risk for having a child with a serious recessive disease.

In the united states, pregnant women are commonly offered carrier screening for sickle trait if African American or latina,thalassaemia trait if mediterranean,asian or African American origin and Tay-sachs trait if Jewish.

• If the women proves to be a carrier, screening is offered to father of the fetus, if he too is a carrier, prenatal diagnosis is offered.

NEWBORN SCREENING New born screening is used just after birth to

identify genetic disorders that can be used early in life.

Blood sample is tested for genetic disorders. All states currently test infants for

phenylketonuria and congenital hypothyroidism.

Benefits-reduced morbidity and mortality of children and cost savings to society.

Risks-parental anxiety about false positive results, harm that causes parent-child relationship.

BENEFITS It provides a sense of relief from uncertainity and

help people make informed decisions about managing their health care.

For eg:negative result: can eliminate need for unnecessary checkups and screening tests in some cases.

Positive result: can direct a person toward available prevention, monitoring an treatment options.

Limitations Risk of losing pregnancy because they

require a sample of amniotic fluid or tissue from around the fetus.

Involves emotionl,social or financial consequences of the test results.

Provide only limited informations about inherited conditions.

Lack of treatment strategies for many genetic disorders once they are diagnosed.

ETHICAL CONSIDERATIONS Should be voluntary Only newborn screening for serious genetic

diseases is commonly mandated. Screenee should make an informed choice, he

should be informed about not just the benefits but also the risks and limitations.

Test result should be confidential Both the biomedical community and the public

need to acquire a better understanding of human genetics