genetic testing

 Genetic testing

Genetic testing is defined as examining a sample of blood or other body fluids or tissue for bio- chemical chromosomal, or genetic markers that indicate the presence or absence of genetic disease.

Or,

A genetic testing is analysing a DNA to look for genetic alteration that may indicate an increased risk for developing a specific disease or disorder.

Or, 

It is also defined as type of medical test, identifies ahanges n chromosomes, gene or proteins.

Reason for genetic Testing

1. Finding genetic disease in unborn child.

2. Finding out if people carry genes for a disease and might pass it on to their children.

3. Screening embroys for disease.

4. Testing for genetic disease in adult before that cause symptoms.

5. Making a diagnosis in a person who has disease symptoms.

6. Figuring out the type or dose 9f medicine that is best for certain person.

 

Purposes

1.Conformational diagnosis of a symptomatic individuals.

2. Forensic or identify testing

3. Pre symptomatic testing for predicting adult onset disorders.

4. It allows the genetic disorder of vulnerabilities to inherited diseases.

Indications for making a genetic Referral

1. Maternal risk factor

2. Prenatal risk factor

Previous child with chromosome problem.

Prepregnancy and prenatal

3. Pediatric risk factor

Previous child birth defect

Previous children mental retardation

Hearing loss, visual impairment

4. Adult condition

Pregnancy history

Hemochromatosis

Exposure to certain medication or drug during pregnancy

Maternal condition; diabetes, epilepsy or alcoholism

Previous miscarriage of 

5. Cancer history

Types of Genetic Testing

Types are;

1. Prenatal testing

2. Newborn screening

3. Diagnostic testing

4. Carrier testing

1. Prenatal testing

It is performed to detect any genetic abnormality in the fetus (genes and chromosomes).

This is type of testing is suggested to couples who are known Carrier or have a previous baby with a genetic or chromosomal disorder.

The genetic testing will help them to decide whether to abort the pregnancy.

2. Newborn screening

In some countries like USA, there is routine testing for infants for certain genetic disorders. Such as; 

Congenital hypothyroidism

Sikle cell anemia

Congenital adrenal hyperplasia

Urine disease

Such genetic disorders can be treated early in life.

3. Diagnostic testing

Diagnostic testing is used to diagnose or rule out a specific genetic or chromosomal condition.

Particular genetic condition suspected based on certain symptoms. Help in management of disease and symptoms.

4. Carrier testing

Screening

Performed vat any time, help in management of disease.

Common Diagnostic Tests

1. Ultrasonography

2. Aminocentesis

3. Chorionic villus sampling (CVS)

1. Ultrasonography

Non-invasive procedure to visualize developing embryo about 6 weeks gestation.

Recognization of major internal organs and extremities to determine if any abnormalities between 16 to 20 weeks.

Ultrasonography useful determination of -

1. The size and position of the fetus

2. The size and position of the placenta

3. The amount of amniotic fluid

4. To appearance of fetal anatomy

Limitation of Ultrasonography

Abnormalities may not be detected until later in pregnancy, or may not be detected at all.

2. Aminocentesis

Invasive procedure.

Performed between 14 and 20 weeks gestation.

In the third trimester of pregnancy, the amniotic fluid can be analyzed for determination of fetal during lung maturity.

Risk factor

Fetal loss

Maternal Rh sensitization

If oligohydramnios is present, then amniotic fluid cannot be obtained.

3. Chorionic villus sampling (CVS)

CVS can be safety performed between 9.5 and 12.5 weeks gestation.

In this procedure, a catheter is passed via the vagina through the cervix and into the uterus to the developing placenta under ultrasound guidance.

The introduction of the catheter allows sampling of cells from the placental chorionic villi.

These cells can than be analyzed by variety of techniques. The most common test employed on cells obtained by CVS is chromosome analysis to determine the karyotype of the fetus.

1. Maternal blood sampling for fetal cells

To Check Fetal blood cells gaining access to maternal circulation through the placental villi.

Fetal cells can be sorted out and analyzed for particular DNA sequencing.

Fluorescence in situ hybridization (FISH)

FISH is one technique that can be applied to identify particular chromosomes of the fetal cells recovered from maternal blood and diagnose aneuploid (presence of abnormal number of chromosomes) condition such as the trisomies and monosomy X.

Problems;

Difficulty to get many fetal blood cells.

May not be enough to reliably determine anomalies of the fetal karyotype or assay for other abnormalities.

4. Maternal serum Alpha Feto Protein

Developing fetus has two major blood proteins; 

1. Albumin

2. Alpha Feto Protein (AFP)

MSAFP test can be utilized to determine the levels of AFP from the fetus.

Only a small amount of AFP gains access to the amniotic fluid and crosses the placenta to mother's blood.

When neural tube defect (NTD) in the fetus.

Escape of more AFP into the amniotic fluid.

Neural tube defects include Spina bifida 

AFP from fetus will end up in maternal blood in higher amounts.

3. Maternal serum beta - HCG

Commonly used test for pregnancy.

Human chorionic gonadotropin; HCG in blood and urine.

Beta-HCG will lower 

Elevated beta - HCG coupled with decreased MSAFP suggest Down syndrome  (trisomy 21).

Very high level of HCG suggest trophoblastic disease (molar pregnancy).

The absence of fetus on Ultrasonography along with an elevated HCG suggests a hydatidiform mole (molar pregnancy).

Some genetic tests provide limited information about an inherited condition.   

May not provide the information about development of the disorder.

Lack of treatment strategies for many Genetics disorders once diagnosed.

Risk associated with genetic testing involves; emotional, social, financial consequences.