Chromosome Microarray

Is Testing Right for Me? I Have My Test Results

Chromosome Microarray

Chromosome Microarrays

Normal human development depends on genes located along the chromosomes. Chromosomes are structures inside your cells that contain all of your genes. If you think of your DNA as a library, each chromosome is a book. Your genes are the chapters inside each book. Each chapter, or gene, contains specific instructions.

Humans have two sets of 23 chromosomes, for a total of 46. There are 22 pairs of autosomes plus one pair of sex chromosomes (the X and Y chromosomes). We inherit one set of chromosomes from our mother and one set from our fathers. Typical female chromosomes are named 46, XX, and typical male chromosomes are 46, XY.

Losses and Gains of DNA

Sometimes, by chance, small pieces of chromosomes are lost (deleted) or doubled (duplicated). Chromosomes can also break and rejoin, which is called a translocation.

Chromosome changes can be large or small. Large rearrangements may be found by looking at a chromosome analysis like in the picture above. This test looks at the "big picture" and can find large changes very accurately. However, chromosome changes can be so small that they can't be seen under the microscope. These kinds of changes are usually microdeletions and microduplications. Labs use an advanced testing technique called chromosome microarray (CMA) to decide whether certain regions are there or not. People who study genetics often group the gains and losses of DNA that can be found with CMA as "copy number variants," or just "CNVs."

Depending on where these chromosome changes happen and how large they are, it may change a person's genes. Having extra or missing copies of genes may change the way a person grows and develops. Such changes may cause mental retardation, birth defects, and/or autism. Some changes have no effect at all.

Next: Who Should Be Tested with Chromosome Microarray?

Why are you considering testing?

I am considering testing for my child who has signs and symptoms of developmental delay and/or autism, but hasn't been diagnosed for sure yet.

I am considering testing for my child who has developmental delay, mental retardation, birth defects and/or other unusual physical features without a known cause.

I am considering testing for my child who has an autism spectrum disorder.

I'm pregnant and considering testing because of birth defects found on ultrasound.

I lost a pregnancy (miscarriage or stillbirth) with birth defects.

None of these.

Chromosome microarray (CMA) testing and other genetic testing can be part of the evaluation for developmental problems, but it isn't the first step.

Evaluations may be needed with doctors and sometimes other specialists to decide whether your child has a health or learning problem. There are many different causes for developmental problems. Doctors need to consider the big picture, and review your child's birth history, medical history, do a head-to-toe exam, and decide what testing might be needed.

Chromosome microarray testing may be useful for your child.

About 10% to 20% of children with mental retardation/intellectual disability, developmental delay, birth defects and other unusual features have a chromosome change that can be found with this testing.

If a chromosome change is found, it is the likely cause of your child's problems. Testing is very accurate. Having information about your child's specific deletion and/or duplication can help guide healthcare decisions. Testing may be useful for other family members (including you as the parent) who are concerned about their reproductive risks.

If no chromosome change is found, a genetic cause of your child's problems can't be ruled out. There may be other changes in genes or chromosomes that can't be found with this testing. There are hundreds of known genetic syndromes that are not checked for with this test.

It is possible to get results from testing that are uncertain. Sometimes chromosome changes are found, and they've never been found before or it's not clear whether they have an effect on development. In order to get more information, testing may be done on both parents to decide whether the change was inherited or is new. Doctors may be able to do research to find out whether the change has been reported in other people and how they were affected by it. However, there are times when a clear answer can't be reached, even with extra testing and research.

Chromosome microarray testing may be useful for your child.

About 7% to 10% of children with autism will have a chromosome change found with testing.

If a chromosome change is found, it is the likely cause of your child's problems. Testing is very accurate. Having information about your child's specific deletion and/or duplication can help guide healthcare decisions. Testing may be useful for other family members (including you as the parent) who are concerned about their reproductive risks.

If no chromosome change is found, a genetic cause of your child's problems can't be ruled out. There may be other changes in genes or chromosomes that can't be found with this testing. There are hundreds of known genetic syndromes that are not checked for with this test.

It is possible to get results from testing that are uncertain. Sometimes chromosome changes are found, and they've never been found before or it's not clear whether they have an effect on development. In order to get more information, testing may be done on both parents to decide whether the change was inherited or is new. Doctors may be able to do research to find out whether the change has been reported in other people and how they were affected by it. However, there are times when a clear answer can't be reached, even with extra testing and research.

Chromosome microarray testing may be useful for your pregnancy.

Overall, about 1% to 3% of pregnancies with birth defects have abnormal test results on chromosome microarray (CMA) when regular chromosome analysis results are normal. Testing may provide you an answer about the cause of the birth defects in your pregnancy. It may give you some answers about what you might anticipate for the future.

If a chromosome change is found, it is the likely cause of birth defects in your pregnancy. Testing is very accurate when a chromosome change is found. Having information about the specific deletion and/or duplication can help guide healthcare decisions. Testing may be useful for other family members (including you as the parent) who are concerned about their reproductive risks.

If no chromosome change is found, a genetic cause of birth defects in your pregnancy can't be ruled out. There may be other changes in genes or chromosomes that can't be found with this testing. There are hundreds of known genetic syndromes that are not checked for with this test.

It is possible to get results from testing that are uncertain. Sometimes chromosome changes are found, and they've never been found before or it's not clear whether they have an effect on development. In order to get more information, testing may be done on both parents to decide whether the change was inherited or is new. Doctors may be able to do research to find out whether the change has been reported in other people and how they were affected by it. However, there are times when a clear answer can't be reached, even with extra testing and research.

If not already done, your doctor may also order a chromosome analysis (also called a karyotype). Around 16% to 30% of pregnancies with birth defects have a larger chromosome change that can be found with that testing. Chromosome analysis sees the "big picture" while CMA finds smaller changes. These two tests each have their benefits and limitations, so doctors use these tests in different ways.

If you've already had prenatal testing done by chorionic villus sampling (CVS) or amniocentesis, you probably won't need to have another procedure done to have CMA testing. Most of the time, the laboratory that handled the original sample can send cells for CMA, if they don't perform the testing themselves.

Chromosome microarray testing may be useful for you.

Testing may provide you an answer about the cause of the birth defects in your pregnancy and whether there is a higher chance for it to happen again. Chromosome microarray (CMA) is usually only done when birth defects are found because pregnancy losses for other reasons are common.

If a chromosome change is found, it was the likely cause of birth defects in your pregnancy. Testing is very accurate. Having information about the specific deletion and/or duplication can help provide an understanding of what caused the birth defects. Testing both parents will be useful to give accurate recurrence risks.

If no chromosome change is found, a genetic cause of birth defects in your pregnancy can't be ruled out. There may be other changes in genes or chromosomes that can't be found with this testing. There are hundreds of known genetic syndromes that are not checked for with this test.

It is possible to get results from testing that are uncertain. Sometimes chromosome changes are found, and they've never been found before or it's not clear whether they have an effect on development. In order to get more information, testing may be done on both parents to decide whether the change was inherited or is new. Doctors may be able to do research to find out whether the change has been reported in other people and how they were affected by it. However, there are times when a clear answer can't be reached, even with extra testing and research.

If not already done, your doctor may also order a chromosome analysis (also called a karyotype). Chromosome analysis sees the "big picture" while CMA finds smaller changes. However, it is sometimes technically difficult to do chromosome analysis on a sample from a pregnancy loss or stillbirth. If chromosome analysis can't be done, CMA can be done alone and still provide useful information.

Depending on the circumstances of your pregnancy loss, fetal autopsy may also be an option. A complete autopsy can often provide answers about the likely cause of birth defects, even if genetic testing is normal.

Chromosome microarray testing may not be useful for you. The main reasons for testing are listed in the Who Should Consider Testing? section.

CMA testing is sometimes used for other health problems, especially cancer. Those uses are not covered by this tool.

If you have a reason for testing that isn't covered here, talk to your doctor or a genetic counselor about whether testing might be useful for you.