Structural genomic alterations can be visualized by several techniques, including chromosome analysis by light microscopy, chromosome microarray analysis (CMA), and fluorescence in situ hybridization (FISH).
A new method, "Optical Genome Mapping", combines the diagnostic potential of CMA (detection of copy number alterations (deletions/duplications) with that of chromosome analysis (visualization of balanced structural aberrations), and FISH (determination of the genomic position of duplications).
Optical genome mapping analysis is performed with high-molecular DNA (average of fragment length: 250 kilobase pairs) labeled with a fluorescent dye. Up to 120,000 single DNA molecules are passed through nano channels and scanned with a laser. The data is mapped to a reference genome, allowing structural variants of the entire genome to be visualized.
Diagnostic advantages of optical genome mapping
Exact breakpoint determination of balanced chromosomal alterations:
- translocation, inversion, insertion<l/li>
Exact breakpoint determination of unbalanced chromosomal alterations:
- deletion, duplication
Characterization of copy number gains:
- direct, inverted, transposed
This makes it possible to investigate complex genomic structural changes in a single diagnostic approach. In addition, it is possible to identify gene disruptions in breakpoint regions.
In Facioscapulohumeral Muscular Dystrophie (FSHD), OGM detects D4Z4 repeat contraction and concomitance of the permissive haplotype.