Because of its rapid turnaround time, fluorescent in situ hybridization (FISH) is commonly used in hospitals and laboratories as an aneuploid screen of cells retrieved from amniocentesis and chorionic villus sampling (CVS). Chromosomes 13, 18, 21, X, and Y are typically screened for aneuploidy in this way. Explain how FISH might be accomplished using amniotic or CVS samples and why the above chromosomes have been chosen for screening.

Verified step by step guidance

1. Step 1: Begin by explaining the concept of fluorescent in situ hybridization (FISH). FISH is a molecular cytogenetic technique that uses fluorescently labeled DNA probes to bind to specific chromosome regions. This allows visualization of specific genetic sequences under a fluorescence microscope.
2. Step 2: Describe the process of sample preparation. Cells from amniotic fluid or chorionic villus sampling (CVS) are collected and cultured. The chromosomes within these cells are then fixed onto a slide to prepare them for hybridization with the fluorescent probes.
3. Step 3: Explain the hybridization process. Fluorescently labeled DNA probes complementary to sequences on chromosomes 13, 18, 21, X, and Y are applied to the slide. These probes bind specifically to their target sequences on the chromosomes, allowing visualization of these regions.
4. Step 4: Discuss the detection and analysis. After hybridization, the slide is examined under a fluorescence microscope. The presence, absence, or abnormal number of fluorescent signals indicates whether aneuploidy (abnormal chromosome number) is present for the screened chromosomes.
5. Step 5: Explain the rationale for choosing chromosomes 13, 18, 21, X, and Y. These chromosomes are associated with common aneuploid conditions, such as trisomy 13 (Patau syndrome), trisomy 18 (Edwards syndrome), trisomy 21 (Down syndrome), and sex chromosome abnormalities (e.g., Turner syndrome and Klinefelter syndrome). Screening these chromosomes provides critical information about the most clinically relevant aneuploidies.

Key Concepts

Fluorescent In Situ Hybridization (FISH)

FISH is a molecular cytogenetic technique that uses fluorescent probes to bind to specific chromosome regions, allowing visualization of chromosomal abnormalities. In the context of amniotic fluid or CVS samples, FISH can quickly identify the presence or absence of specific chromosomes, making it a valuable tool for detecting aneuploidies, such as trisomy or monosomy.

Aneuploidy

Aneuploidy refers to an abnormal number of chromosomes in a cell, which can lead to genetic disorders. Common aneuploidies include trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome). Screening for these specific chromosomes during prenatal testing is crucial because they are associated with significant developmental and health issues.

Amniocentesis and Chorionic Villus Sampling (CVS)

Amniocentesis and CVS are prenatal diagnostic procedures used to obtain fetal cells for genetic analysis. Amniocentesis involves extracting amniotic fluid, while CVS involves sampling placental tissue. Both methods provide valuable samples for FISH analysis, enabling early detection of chromosomal abnormalities in the fetus.