Comparative genomic hybridization (CGH) is an innovative genetic test that detects small-scale changes in the DNA that can cause genetic disorders.
The test is recommended in cases of a risk for genetic disorders, such as in children with intellectual impairment or during the pregnancy when fetal development delays are detected.
Biochip testing is based in a unique molecular technology that allows a high-resolution detection of genetic disorders needed for explaining medical findings.
When is the test needed?
CGH tests provide more information than conventional genetic tests, such as karyotyping or FISH tests. While karyotype tests or FISH tests use a microscope to analyze chromosomes, CGH tests use advanced molecular biology technologies that allow detection of small-scale genetic changes.
Unlike karyotyping that is mainly used to detect large-scale chromosome aberrations (missing or excess chromosomes or chromosome translocations where part of one chromosome incorrectly attaches to another chromosome) CGH detects small changes that would go undetected under the microscope, which enables diagnosis of a wider range of genetic disorders.
In addition, whereas FISH tests require a suspicion for a specific genetic disorder (such as through family history), CGH screens the entire DNA and detects all changes regardless of a previous specific suspicion.
For these reasons, CGH testing is mainly recommended to determine the cause for intellectual or developmental impairment in children or when a genetic disorder is suspected during the pregnancy following fetal development delays. In these cases, CGH tests can provide more extensive and precise information that allows genetic counsellors to determine whether the disorder has a genetic cause.
Who should take the test?
CGH tests (biochip) are usually recommended to two main groups:
Children or adults with intellectual disability or developmental delay
In some cases of developmental delay or intellectual disability in children, doctors look for a genetic explanation for these conditions. Identifying a genetic disorder such as missing or excess genetic material could help explain the intellectual impairment.
In addition, CGH tests are sometimes recommended to adults with intellectual disabilities, to help prove the cause for these conditions is genetic. Since these are relatively new tests, these patients did not undergo it during childhood, but can undergo it today to help diagnose their disorder through biochip technologies.
How does the test work?
In CGH testing, DNA from the patient is compared to a control DNA sample from a healthy individual. In prenatal testing, fetal DNA is sampled through amniocentesis. In children or adults, DNA is taken from a blood test or saliva sample.
After creating the DNA sequences, they are compared to the control DNA sample using fluorescent dyes. These dyes mark the patient’s DNS in red and the healthy control sample in green.
Mixing the two DNA sequences creates a fluorescent picture that can provide extensive information on excess or missing DNA. since equal amounts of DNA are mixed, an equal amount of DNA will show dyed in yellow, while an excess will be marked in red and missing DNA will show in green.
What disorders can the test detect?
CGH testing can detect any genetic disorder that reflects in intellectual disability, developmental delay, or autism.
When ultrasound tests show signs of fetal development delay, CGH results can help identify intellectual disability and other developmental disorders, which makes these tests highly important.