A microarray test is a genetic test that examines a person’s DNA to detect missing or duplicated segments. This laboratory technique provides a comprehensive overview of genetic material, serving as a valuable tool in medical diagnostics for uncovering genetic causes of various health conditions.
How the Test Works
A microarray test relies on DNA hybridization, where complementary single-stranded DNA molecules bind. The process begins by extracting DNA from a patient’s sample. This patient DNA is labeled with a fluorescent dye, and a reference DNA sample (representing a typical genetic makeup) is labeled with a different fluorescent dye. Both DNA samples are then fragmented.
These fragmented DNA samples are applied to a microarray chip, a glass slide with thousands of microscopic spots. Each spot contains millions of copies of specific DNA sequences called probes, designed to correspond to particular regions of the human genome. The labeled patient and reference DNA fragments hybridize to their complementary probes on the chip.
After hybridization, the chip is washed, and a laser scanner reads the fluorescent signals from each spot. The scanner detects the ratio of patient to reference fluorescence at each probe location. Equal amounts indicate a normal DNA amount. Higher patient fluorescence suggests a DNA duplication, while higher reference fluorescence indicates a deletion. Computer software then analyzes these fluorescence patterns to identify any imbalances in the patient’s DNA.
What the Test Identifies
A microarray test primarily identifies copy number variants (CNVs), which are segments of DNA present in an abnormal number of copies. These include microdeletions (missing genetic material) and microduplications (extra copies). Unlike traditional karyotyping, microarray offers much higher resolution, detecting changes as small as a few thousand DNA base pairs.
The test does not detect single-nucleotide changes (point mutations) or balanced chromosomal rearrangements, where genetic material is rearranged but not gained or lost. Instead, microarray focuses on quantitative changes in DNA content across the entire genome, providing information on gains and losses of genetic material that can impact gene function.
Common Applications
Microarray testing is widely used in clinical settings, especially in pediatric genetics, to diagnose developmental conditions. It is often ordered for children with unexplained developmental delays, intellectual disabilities, or autism spectrum disorders. The test can identify specific genetic syndromes, providing a diagnosis that guides management and prognosis.
The test is also a diagnostic tool for individuals with multiple congenital anomalies (birth defects). In prenatal diagnosis, microarray may be recommended when ultrasound reveals fetal structural abnormalities like heart defects or brain malformations. Identifying a CNV helps parents understand implications for their child’s health and development and can inform future reproductive planning.
Interpreting Test Results
Interpreting microarray test results involves classifying detected DNA changes by clinical significance. A “normal” or “negative” result means no clinically significant copy number variants were found. While reassuring, this does not rule out all genetic conditions, as the test does not detect all types of genetic changes.
An “abnormal” or “positive” result signifies a pathogenic or likely pathogenic copy number variant. A pathogenic CNV is a DNA gain or loss known to cause a specific genetic disorder or strongly associated with symptoms. Such a finding provides a definitive genetic diagnosis, informing medical management, prognosis, and genetic counseling. The CNV’s size and encompassed genes determine its clinical impact.
A third category is a “variant of uncertain significance” (VUS). A VUS is a copy number variant not previously reported or whose disease association is unknown. This means a DNA change has been identified, but medical professionals do not yet have enough information to determine if it is harmless or contributes to the patient’s condition. Further investigation, including family testing, may clarify its significance. Genetic counseling helps patients and families understand complex results, especially VUS findings, and discuss health implications.