Genetic testing: Microarray

What is a microarray?

A microarray is a genetic test that can detect small missing (deletions) or extra pieces (duplications) of chromosomes. It can help identify the underlying cause of your child’s medical condition. A microarray is also known as chromosomal microarray, array-based comparative genomic hybridization (aCGH) or single nucleotide polymorphism (SNP) microarray.

What are the benefits of doing a microarray?

The results of a microarray may provide a diagnosis for your child’s condition and answers for your family. A diagnosis may help with learning the associated medical or health risks of your child’s condition, accessing the appropriate resources for your family, informing other family members of potential risks (if any), and informing decisions around future pregnancies.

Genetics and microarray

Chromosome deletion

Our bodies are made up of millions of cells. Inside our cells are chromosomes, which are string-like structures that contain our genetic information (genes). Microarray analysis looks at the chromosomes at a submicroscopic level to find small deletions or duplications of genetic information, also known as copy number variation (CNV).

How is a microarray done?

A blood sample is taken from your child and sent to the lab. DNA is extracted from the sample and compared to a control sample to detect any small extra or missing pieces of chromosomes that cannot be detected under a microscope. A normal microarray result does not rule out a possible underlying genetic cause of your child's condition. Microarrays only look at your child’s chromosomes and not at specific genes.

Preparing for the test

There are no preparations needed before completing a microarray test. Your child can eat and drink as usual.

How to interpret microarray results

There are three major types of test results that can be reported from a microarray:

• Pathogenic/likely pathogenic: the small extra or missing piece of chromosome identified explains or likely explains your child’s condition.
• Variant of uncertain significance (VUS): there isn't enough information available currently to say whether the small extra or missing piece of a chromosome explains your child's condition or is harmless. Finding a VUS is common and not all VUSs are pathogenic. If you are the biological parent of your child, you may be requested to provide a blood sample to help with interpretation.
• Benign/normal: your child's sample matches the control sample (i.e., no small extra or missing pieces of chromosomes were identified).

Absence of homozygosity (AOH) is another result that can be interpreted from a microarray. AOH means there are areas detected on a microarray where one or more chromosomes are identical. This is not always an abnormal result and can be seen in healthy individuals; however, AOH can raise the possibility of an underlying genetic disorder.

Your child’s health-care provider who ordered the microarray test will talk to you about the test results. A referral to a genetic counsellor and/or a geneticist may be made.