MLPA: What It Is, How It Works, and What It Tests For

What Is MLPA?

MLPA stands for Multiplex Ligation-dependent Probe Amplification. It is a laboratory method used to look at specific parts of a person's DNA to find missing pieces (deletions) or extra copies (duplications). Unlike tests that read the exact spelling of every DNA letter, MLPA checks whether entire sections of a gene or chromosome are present in the expected number. Doctors use it when they suspect a genetic condition caused by these kinds of changes, which are too small to see under a microscope but too large to be caught by standard sequencing.

How the MLPA Test Works

The process starts with a small sample of the patient's DNA, usually drawn from blood. In the lab, technicians mix the DNA with probes — short artificial DNA pieces designed to bind to specific target areas. Each probe has two halves that only connect when they are right next to each other on the DNA strand. Once the probes ligate, or join together, the lab uses a process called PCR to make millions of copies so the signal can be measured. By comparing the amount of each probe's signal to normal control probes, the lab can tell whether a target region is deleted, duplicated, or present at the expected level.

Conditions MLPA Can Detect

MLPA is used to screen for a wide range of genetic disorders. The exact probe sets a lab runs depend on what the doctor suspects. Common applications include testing for spinal muscular atrophy, certain forms of muscular dystrophy such as Duchenne and Becker, and genetic conditions linked to developmental delay or intellectual disability. It is also used in cancer genetics to check for missing or extra copies of tumor suppressor genes or oncogenes, which can influence a person's risk or guide treatment decisions.

MLPA vs. Other Genetic Tests

MLPA fills a specific niche. Standard gene sequencing reads individual letters of DNA and is excellent for finding small spelling changes called point mutations. Chromosomal microarray analysis looks across the whole genome for large missing or extra segments. MLPA sits between these two: it targets specific regions with high sensitivity but does not scan the entire genome. This makes it faster and less expensive than a full microarray when the area of interest is known in advance.

What MLPA Results Mean

A typical MLPA report compares the signal from each probe to a control group. Probes that show reduced signal may indicate a deletion, while probes showing increased signal may point to a duplication. Some results come back as normal, meaning no change was found in the regions tested. A result that is unclear or variant of uncertain significance may require follow-up testing, such as sequencing the specific gene or testing other family members to see if the change was inherited. Genetic counseling is often recommended to help interpret what the results mean for the patient's health and for relatives.

Limitations of MLPA

MLPA only looks at the regions its probes are designed for. If a deletion or duplication falls outside those targets, the test will miss it. It cannot detect balanced rearrangements, where DNA swaps locations without any net loss or gain. Point mutations and very small changes within a gene also require a different method. Because of these limits, doctors sometimes order MLPA alongside other tests to build a complete picture.

Who Might Be Offered MLPA

A doctor may order MLPA when a patient has symptoms that suggest a known deletion or duplication syndrome, or when a previous test such as sequencing came back negative but clinical suspicion remains high. Prenatal and pediatric cases are common scenarios, though adults may also be tested for late-onset conditions or carrier status. Insurance coverage and test availability vary, so the ordering clinician usually works with a genetics lab to confirm the right probe mix is ordered for the specific clinical question.