What is Karyotyping?
- Karyotyping or Chromosome analysis is a test conducted in laboratory to examine chromosomes in a sample of cells.
- This test is performed to examine the number and structure of chromosomes in a cell and thus can help to identify genetic problems as the cause of a disorder or disease.
- Karyotyping sorts and displays these chromosome pairs by size, shape, and banding pattern. The resulting picture is called a
- Certain problems can be identified through the number or arrangement of the chromosomes.
The test can be performed on almost any tissue, including
- Amniotic fluid– Amniotic fluid is a clear, slightly yellowish liquid that surrounds the unborn baby (fetus) during pregnancy. It is contained in the amniotic sac. The amniotic fluid test is done to check a developing baby for chromosome problems. To test amniotic fluid, an amniocentesis (a test that can be performed during pregnancy to look for certain problems like birth defects, genetic problems, infection and lung development in the developing baby) is done.
- Blood
- Bone marrow- A bone marrow biopsy (Removal of marrow from inside one of your bones) is needed to take a sample of bone marrow. The sample is placed into a special dish or tube and allowed to grow in the lab. Cells are later taken from the new sample and stained. The lab specialist uses a microscope to examine the size, shape, and number of chromosomes in the cell sample. The stained sample is photographed to show the arrangement of the chromosomes. This is called a karyotype.
The bone marrow or blood test can be done to identify the Philadelphia chromosome, which is found in 85% of people with chronic myelogenous leukemia (CML). - Tissue from the organ that develops during pregnancy to feed a growing baby (placenta).
How the Test Works
- Sample collection: Technicians take cells from blood, bone marrow, amniotic fluid, or tissue.
- Cell growth: Cells grow in a lab dish and are stopped during division (metaphase stage) when most condensed.
- Staining: Special dyes (like Giemsa) create light and dark bands on the chromosomes. G-banding or Giemsa banding is a DNA staining technique that is used to visually investigate the structure of condensed chromosomes within the nucleus of a cell.
- Analysis: A specialist views and analyses the chromosomes under a microscope to spot abnormalities.
Application
- On a couple that has a history of miscarriage
- To examine any child or baby who has unusual features or developmental delays.
Apart from that, some other tests along with karyotyping may be asked by your provider, these are-
- Microarray: Looks at small changes in the chromosomes.
- Fluorescent in situ hybridization (FISH): Looks for small mistakes such as deletions in the chromosomes
Normal & Abnormal Results
Normal Results: In case of females, 44 autosomes (non-sex chromosomes) and 2 sex chromosomes (XX), written as 46, XX, whereas in males, 44 autosomes and 2 sex chromosomes (XY), written as 46, XY.
Abnormal Results: Abnormal results may be due to a genetic syndrome or condition, such as,
- Down syndrome: a genetic condition in which a person has 47 chromosomes instead of the usual 46.
- Klinefelter syndrome: also called 47, XXY, is a genetic condition that occurs in males when they have an extra X chromosome.
- Philadelphia chromosome.
- Trisomy 18: Trisomy 18 is a genetic condition in which a person has a third copy of material from chromosome 18, instead of the usual 2 copies.
- Turner syndrome: Turner syndrome is a rare genetic condition in which a female does not have the usual pair of X chromosomes.
Chemotherapy may cause chromosome breaks that affect normal karyotyping results.
Medical Uses
- Genetic disorders: Detects extra or missing chromosomes (aneuploidy).
- Syndromes: Diagnoses conditions like Down syndrome (extra chromosome 21), Turner syndrome (missing X chromosome), or Klinefelter syndrome (extra X chromosome in males).
- Cancer: Identifies damaged or rearranged chromosomes in leukemias and lymphomas.
- Prenatal testing: Checks fetal cells during pregnancy for birth defects.