From Medicineworld.org: Prenatal Test: Detection Of Genetic Disorders
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Prenatal Test: Detection Of Genetic Disorders
"It's the beginning of a sea change in prenatal diagnosis," said Dr. Arthur Beaudet, chair of molecular and human genetics at BCM. "You are going to be able to detect a range of the most severe conditions, and in the future this can be cheaper than current methods hopefully using a very noninvasive approach." The new test can find more disorders and is as at least as fast as prior techniques.
The technique could even lead to more general use of prenatal screening for these disorders, said Beaudet.
The new test uses a gene chip or microarray to analyze various areas of the human genome for abnormal regions that contain too a number of or too few copies of the genetic material. These gains or losses in DNA can lead to devastating genetic conditions that present serious disabilities for the lives of children born with them.
The microarray or gene chip is like a map that is covered with tiny dots consisting of DNA from known locations on each of the 46 chromosomes. DNA from the patient is labeled one color (for example, red), and DNA from a normal person (control) is labeled another color (in this example, green). The two DNAs are then mixed and added to the microarray. The appropriate part of the genome seeks out the appropriate dot of DNA on the chip and attaches to it. If the DNA in both patient and control is normal, then the two colors of the dye even out and that dot turns yellow. If there is too much DNA (as happens when there are three instead of two copies of a region or an entire chromosome), the dot is more red because there is more of the patient's DNA. If there is too little, the dot is greener because there is more of the control's DNA and less of the patient's.
Beaudet says the new test can accurately identify many chromosomal disorders early in pregnancy that prior screens could not. Among the disorders that this technique will detect are DiGeorge, Williams, Angelman, and Prader-Willi syndromes. It also detects a variety of gains or losses towards the ends (telomeres) of the chromosomes, which are important causes of a number of developmental disability syndromes.
For women already having amniocentesis or chorionic villus sampling, the new test can be an added analysis on the sample with no added risk. The risk of amniocentesis and chorionic villus sampling to the fetus is even less than has been suggested in the past. The procedure-related risk of amniocentesis is probably only 1:400-500, says Dr. Joe Leigh Simpson, chair of OB/GYN at BCM. Investigators at the University of California at San Francisco have suggested that it is cost-effective to offer traditional amniocentesis to all pregnant women.
"Offering the test to all pregnant women becomes even more attractive using the newer form of prenatal testing because it combines tests for a number of additional diseases," Beaudet said. Women may increasingly be offered the choice of going straight to amniocentesis or chorionic villus sampling rather than the blood tests and ultrasound tests that are currently used to estimate risks of Down syndrome and decide which women are candidates for amniocentesis.
The comprehensive BCM test is expected to cost approximately $1,900 in addition to the usual costs for amniocentesis and prenatal testing. Procuring the same results using separate, conventional tests would cost around $20,000.
Beaudet believes the price of the BCM procedure will drop considerably within the next few years. With better understanding of how to obtain fetal cells from the mother's body, it may ultimately evolve into an automated test as noninvasive as a pap smear or a maternal blood sample and cost a few hundred dollars.
"This test is going to get cheaper and give you more information over time, which is unusual compared to most medical technology," said Beaudet, who anticipates that insurance companies will eventually cover the screening costs.
More information about the test can be obtained by calling 1-800-411-4363 or by visiting the Chromosomal Microarray Analysis web site. http://www.bcm.edu/cma/.
Source: Bylor College of Medicine
Did you know?
A new chromosomal test developed at Baylor College of Medicine in Houston can now alert pregnant women to an array of fetal disorders otherwise undetectable by conventional tests. This testing is discussed in a commentary and editorial in today's edition of the journal Nature.
Medicineworld.org: Prenatal Test: Detection Of Genetic Disorders
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