According to a study which involved more than 4,000 participants, more information about potential disorders can be obtained using chromosomal microarray (CMA) to test a developing fetus' DNA, than the standard method of prenatal tests, which is used to visually analyze the chromosomes (karyotyping).
The 34-center study, funded by Eunice Kennedy Shriver National Institute of Child Health and Human Development, was recently published in the American Journal of Obstetrics & Gynecology. Results from the study were presented on February 9, 2012, at the 32nd annual meeting of the Society for Maternal-Fetal Medicine in Dallas.
The researchers found that in women undergoing routine prenatal diagnosis, CMA identified additional genetic abnormalities in approximately 1 out of every 70 fetal samples that had a normal karyotype. In 6% of cases, CMA identified additional important genetic information when a birth defect was imaged by ultrasound.
According to Dr. Ronald Wapner, director of Reproductive Genetics at NewYork-Presbyterian Hospital/Columbia University Medical Center, vice chairman for research and professor of obstetrics and gynecology at Columbia University College of Physicians and Surgeons, results from the study indicate that karyotyping could soon be replaced by CMA for prenatal testing.
Dr. Wapner explains:
"Why would anyone want to continue to use the standard method, which gives only part of the answer? However, we will have to carefully transition this information into clinical practice-to educate physicians and patients, develop guidelines for its use, and learn how to best use it to improve care."
CMA has become the primary genetic test to assess infants and children with developmental delays and newborns with birth defects, although it is not routinely used for prenatal testing. Dr. Wapner said:
"With karyotyping, we can see only when pieces of the genome of about 5 million base pairs are missing from a chromosome. With CMA, we can see missing pieces of fewer than 100,000 base pairs."
CMA is based on a technique that finds out if the correct amount of genetic material is present at several locations in the fetus' genome.
The study was the first to assess and compare the two techniques. In 4,450 participants, the researchers collected samples from the placenta or the amniotic fluid.
Dr. Wapner explains:
"These were women who were seeking prenatal testing for the usual reasons, which could be age, increases risk of inheritable disease, or a structural abnormality in the fetus."
In a blinded fashion, the researchers split and sent each of the participant's samples to 1 of 4 laboratories that conduct CMA-NewYork-Presbyterian Hospital/Columbia University Medical Center, Baylor University, Signature Genetics, or Emory University. The other half of the sample was transferred to Genzyme Genetics for standard karyotyping.
Although results revealed that both karyotyping and CMA were effective at detecting chromosomal abnormalities, such as the duplicate chromosomes that cause Trisomy 18 and Down syndrome, CMA gave considerably more clinically relevant data in two situations.
Dr. Wapner, said:
"In 6 percent of the cases where there's a structural abnormality of the fetus but karyotyping is normal, CMA will provide additional significant information. And in about 1.7 percent of cases where the procedure was done because of the mother's age or similar concerns and the chromosomes were normal, CMA reveals additional information of concern."
Both CMA and karyotyping can signal a potential health threat that might be treatable or provide information on conditions that can be life-threatening to a newborn baby. Dr. Wapner explained:
"We are looking for the same thing in both tests. But we find more abnormalities with CMA."
At least 150 known conditions can be detected using CMA. In addition, the method allows researchers to see exactly what the problem is and what it means for the child. Even though the same kind of information can be obtained using karyotyping, CMA is more likely to provide further information on other possible disorders that otherwise may not have been identified, such as autism or intellectual disability.
Dr. Wapner explained:
"It does not always mean that a child will necessarily develop these disorders, because many are due to multiple influences. But it will help parents because they can be on the lookout for a particular disorder and have a treatment plan in place. I believe it is important to give parents as much information as they need about their child."
Written by Grace Rattue