Question

Define or describe the following technologies: a. FISH b. amniocentesis c. chorionic villus sampling d. cell-free fetal DNA analysis

Short answer

FISH is a technique for detecting specific DNA sequences. Amniocentesis is a procedure used to sample amniotic fluid for prenatal testing. Chorionic villus sampling is a prenatal test for diagnosing chromosomal abnormalities. Cell-free fetal DNA analysis is a non-invasive prenatal test that analyzes fetal DNA in the mother's blood.

Step-by-step solution

Defining FISH

FISH, or Fluorescent In Situ Hybridization, is a molecular cytogenetic technique that uses fluorescent probes to detect and localize the presence or absence of specific DNA sequences on chromosomes. It can be used to help diagnose a variety of genetic diseases.

Describing Amniocentesis

Amniocentesis is a medical procedure used in prenatal diagnosis, where a small amount of amniotic fluid is sampled from the amniotic sac surrounding a developing fetus. This fluid can be analyzed to detect abnormalities in the baby's genes or chromosomes.

Explaining Chorionic Villus Sampling

Chorionic Villus Sampling (CVS) is a prenatal test that diagnoses chromosomal abnormalities and other inherited diseases. During the procedure, a small sample of cells (called chorionic villi) is taken from the placenta where it attaches to the wall of the uterus.

Clarify cell-free fetal DNA analysis

Cell-free fetal DNA analysis is a non-invasive prenatal test that analyzes cell-free DNA from the fetus that circulates in the mother’s blood. It can provide information about the likelihood that the fetus has certain genetic disorders, such as Down Syndrome.

Key concepts

Fluorescent In Situ Hybridization (FISH)

Fluorescent In Situ Hybridization (FISH) is a vital genetic test allowing researchers and clinicians to visualize specific genes or portions of genes in the context of an individual's chromosomes. The letters in FISH stand for:

• Fluorescent: because it uses fluorescent dyes to label the probes.
• In Situ: meaning 'in place' or 'on site' to indicate that the testing is done on the intact cells.
• Hybridization: referring to the binding of the probe to the complementary DNA sequence within the chromosome.

When performing FISH, probes—tiny bits of fluorescently labeled DNA—are used to stick to the parts of the chromosome with a high degree of sequence complementarity. Under a special microscope, these probes glow, pinpointing the location of the genes or genetic changes of interest. FISH is often used for finding specific features in DNA for use in genetic counseling, medicine, and species identification.

Amniocentesis

Amniocentesis is a prenatal diagnostic procedure that's critical for detecting chromosomal abnormalities and other genetic conditions in a developing fetus. In this procedure, a thin needle is inserted through the mother's abdominal wall and into the uterus to draw a small sample of amniotic fluid—the liquid that surrounds and protects the fetus.

This fluid contains fetal cells that can provide a wealth of genetic information. Analysis of these cells can diagnose conditions like Down syndrome, cystic fibrosis, or spinal muscular atrophy. Because amniocentesis involves penetrating the amniotic sac, there is a slight risk of complications, such as miscarriage or leakage of amniotic fluid. It is generally offered when there are identified risks or family history suggesting a heightened risk of genetic disorders.

Chorionic Villus Sampling

Chorionic Villus Sampling (CVS) offers an earlier detection of potential genetic issues during pregnancy compared to amniocentesis. This test usually takes place between the 10th and 12th weeks of gestation. A small sample of chorionic villi—tiny finger-like projections that line the placenta and share the fetus's genetic makeup—is obtained.

The sample can be collected either through the cervix (transcervically) or the abdominal wall (transabdominally), depending on several factors, including the position of the placenta. The obtained villi cells carry the same genetic information as the fetal cells and are used to detect genetic disorders. The risks involved with CVS are comparable to those of amniocentesis, including a small risk of miscarriage.

Cell-free Fetal DNA Analysis

As a significant advancement in prenatal screening, cell-free fetal DNA analysis provides genetic information about the fetus without the need for invasive procedures. During pregnancy, small fragments of the fetus's DNA are released into the mother's bloodstream. These can be sampled through a regular blood draw from the mother.

This non-invasive test analyzes this cell-free DNA for abnormalities, especially for aneuploidies, which are conditions characterized by an abnormal number of chromosomes, such as Down syndrome, Patau syndrome, and Edwards syndrome. Because this test only requires a simple blood sample, the risks to the fetus are minimal, making it an attractive option for early screening. However, it's important to note that while cell-free fetal DNA analysis can indicate potential genetic issues, it does not confirm a diagnosis. Further diagnostic testing may be required to validate any findings.