Chromosome Microarray (CMA) Testing
The genetic material of a human, DNA, is located in most of the body’s cells and is organized into structures called chromosomes.
Human cells normally contain 23 pairs of chromosomes, divided into 22 pairs of autosomes + one pair of sex chromosomes XX and XY, for a total of 46 chromosomes.
In the event of extra or missing chromosomes, normal fetal development may be impaired, and there is a higher miscarriage prevalence. In addition, an infant born with an abnormal chromosomal material may carry congenital deficiencies, cognitive dysfunction, or other health problems.
One of the most recognized deficiencies is Down syndrome, caused by chromosome number 21 having three copies instead of two. The additional copy of the chromosome changes how the body and the brain develop. In addition to Down syndrome, other chromosomal abnormalities can occur due to quantitative changes in the fetus's genetic material.
To examine the fetus’s chromosomes during pregnancy, diagnostic tests such as chorionic villus sampling (CVS) or amniocentesis can be performed. The genetic material sample collected through these tests is sent to a lab where it is analyzed through the Chromosomal Microarray Method (CMA). CMA is a quantitative molecular test that examines the fetus’s chromosomes for changes in the amount of chromosomal material, such as extra or missing chromosomes. Due to its high sensitivity, CMA can detect even small (sub-microscopic) changes. This allows for the identification of numerous significant variations in fetal DNA, including Down syndrome.
Please note:
- The CMA may reveal non-conclusive findings, making it difficult for parents to decide about continuing the pregnancy. During pre-test counseling, it is possible to choose not to receive unclear or non-conclusive information, as is common practice in many countries internationally.
- Studies have shown that even when pregnancies have normal pregnancy monitoring, including nuchal translucency, screening tests, and ultrasound examinations, the CMA may produce an abnormal result (1 in120).
Test schedule and receipt of results
The CMA is performed on the genetic material sample collected through chorionic villus sampling (CVS), typically performed between weeks 11 to 13 of pregnancy, or amniocentesis, typically performed between weeks 16 to 22.
The results of the CMA test are typically available within three weeks.
Analysis of results
A normal result: 22 pairs of autosomal chromosomes and one pair of sex chromosomes (XX in females, XY in males) – a total of 46 chromosomes.
An abnormal result: If the result is abnormal, its meaning will be explained as part of genetic counseling.
Abnormal results include:
- Extra copies (multiplies) of whole chromosomes, such as trisomy 21, 13, 18, or sex chromosomes (triple X).
- Lack of whole chromosomes, such as the X chromosome (Turner syndrome).
- Additions or lack of chromosome parts, whose implications rely on the location and size of the evidence.
Please note that sometimes the result indicates a variation with an uncertain significance (VUS – Variant of Uncertain Significance).
Paying for the test
Under the National Health Insurance Law, any pregnant woman who undergoes genetic counseling and receives a recommendation to undergo a diagnostic test (chorionic villus sampling or amniocentesis), for any reason (abnormal finding/maternal age/abnormal nuchal translucency/increased risk in screening tests, etc.), is entitled to receive the genetic chip test free of charge, performed on the sample that was taken, provided that all the tests are conducted within the public health system, without any private provider.