Array-based comparative genomic hybridisation (array-CGH) is performed on a child with unexplained developmental delay and dysmorphic features. The test compares differently labelled patient and control DNA co-hybridised to an oligonucleotide array. A deletion is reported when the array shows:

• A Excess red fluorescence, indicating gain of patient DNA at that locus
• B Equal red and green fluorescence across all loci
• C Excess green fluorescence, indicating loss of patient DNA at that locus ✓
• D No hybridisation signal anywhere on the array

Explanation

In array-CGH, control DNA is conventionally labelled red and patient DNA green. Where the patient has a deletion, less green-labelled patient DNA hybridises, so the red-to-green ratio rises and the spot reads as relatively red-dominant loss of patient material. Equal fluorescence indicates no dosage change, and global signal failure suggests technical problems rather than a focal deletion. Note that some laboratories invert the colours, so reporting depends on the stated scheme.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.