Multiplex Ligation-dependent Probe Amplification is a specialised genetic test that checks whether a person has the correct number of copies of specific parts of a gene, rather than checking the exact letter-by-letter spelling of the gene.

To understand this simply: think of a gene as a chapter in a book. Most genetic tests (such as sequencing) check whether any word in that chapter is misspelled. This test instead checks whether any pages of that chapter are missing (deletion) or duplicated (duplication). Both types of errors can cause disease, but they need different tools to detect.

Specifically, this technique can detect:

*A single exon deletion (one small segment of a gene missing)
*A single exon duplication (one small segment present in extra copy)
*Multiple exons deleted or duplicated together
*An entire gene deleted or duplicated
*In extended versions of the test, larger chromosomal gains or losses, and changes in gene methylation (a chemical marking on genetic material that affects whether a gene is switched on or off)

This makes it especially useful for picking up genetic changes that standard sequencing can miss entirely, because sequencing is designed to read letters, not count copies.