Learning Objective: At the end of this lesson, the learner will be able to describe the principle, procedure, and clinical applications of karyotyping and identify chromosomal abnormalities associated with genetic disorders and cancers.
Karyotyping is a laboratory technique used to visualize and analyze chromosomes to detect structural or numerical abnormalities.
It is commonly used for:
- Prenatal diagnosis of chromosomal disorders
- Cancer cytogenetics
- Investigation of infertility or recurrent pregnancy loss
Principle and Procedure
- Cell culture: Cells are cultured from blood, bone marrow, amniotic fluid, or placental tissue.
- Mitotic arrest: Colchicine is added to disrupt spindle fiber formation and arrest cells in metaphase, when chromosomes are most condensed and visible.
- Staining: Chromosomes are treated with stains (e.g., Giemsa) to reveal banding patterns.
- Analysis: Chromosomes are arranged according to:
- Size
- Centromere position (arm-length ratio)
- Morphology
- Banding pattern
- Interpretation: Abnormalities such as trisomies, monosomies, translocations, deletions, or duplications can be detected.
Example:
- Trisomy 21 → Down syndrome
- Turner syndrome → 45, X
- Klinefelter syndrome → 47, XXY
- Cancer cells often show extensive chromosomal rearrangements.
Clinical Applications
| Sample Type | Use |
|---|---|
| Peripheral blood or bone marrow | Diagnosis of leukemia or lymphoma cytogenetic abnormalities |
| Amniotic fluid | Prenatal detection of autosomal trisomies or sex chromosome disorders |
| Placental tissue | Early prenatal diagnosis |
| Other tissues | Detection of structural chromosomal abnormalities in tumors |
High-Yield Tip
- Colchicine arrests cells in metaphase by inhibiting microtubule polymerization.
- Banding patterns allow precise identification of individual chromosomes.
- Karyotyping is a first-line tool for detecting gross chromosomal imbalances; smaller mutations require FISH or microarray.
