Preparatory Mindset

Study this chapter with focus on how genetic principles affect clinical practice.

Core Concepts

• Indications for karyotype: Multiple congenital anomalies, intellectual disability, infertility, recurrent miscarriage, suspected aneuploidy, hematologic malignancies


• Cancer cytogenetics: Many cancers have specific chromosomal abnormalities (e.g., Philadelphia chromosome t(9;22) in CML)


• FISH (Fluorescence In Situ Hybridization): Targeted — detects specific sequences. Rapid (24-48h). Best when you KNOW what you're looking for.


• Array CGH: Genome-wide detection of copy number gains/losses. Cannot detect balanced translocations or inversions.


• ISCN nomenclature: Standardized karyotype description: 46,XX,del(5)(p15.3) = cri-du-chat syndrome


• Mosaicism: Different karyotypes in different cell lines from same individual → may need multiple tissues to detect

High-Yield Points

• FISH = targeted (known abnormality); Array CGH = genome-wide (unknown)


• Karyotype indications: MCA, ID, infertility, recurrent miscarriage


• Balanced translocations: normal phenotype in carrier → risk of unbalanced gametes

Topic Summary

Clinical cytogenetics applies chromosome analysis to patient care. Choose testing method based on clinical question.