11 December 2012

Genetic prenatal diagnostics is much more informative than traditional methods

Traditionally, pregnant women are offered an ultrasound examination or a blood test to identify the risk of having a child with serious genetic abnormalities, such as Down's disease. However, these methods can only determine the level of risk and do not provide unambiguous answers to questions.

The next informative stage is the diagnostic study of fetal cells obtained by amniocentesis (puncture of amniotic fluid carried out through the mother's abdomen), or biopsy of chorionic villi, which consists in removing a fragment of the placenta. Specialists analyze the karyotype of isolated cells under a microscope to identify additional copies or serious chromosome breakdowns, which allows diagnosing a little more than a dozen serious diseases.

As part of a multicenter study planned and supervised by specialists from Columbia University Medical Center, scientists compared the informative value of visual examination of chromosomes with the informative value of scanning the genome using chips that allow detecting hundreds of anomalies caused by DNA defects indistinguishable under the microscope. The cost of such an analysis is $ 1,200-$ 1,800; for comparison, the cost of traditional visual analysis of a karyotype in the United States fits into the range of $ 600-1,000.

The study involved 4,400 pregnant women who were examined in 29 clinics in the United States. Half of the participants were in the high–risk group, since their age exceeded 35 years; 20% had screening test results indicating the likelihood of having a child with Down syndrome; another 25% had ultrasound results indicating possible structural abnormalities. The remaining women expressed a desire to participate in the study for other reasons. All participants were examined by both traditional and genetic methods.

As a result, with the help of genetic analysis, 6% of women whose ultrasound results indicated possible structural defects of the fetus in the absence of genetic disorders determined by visual analysis of chromosomes revealed certain genetic abnormalities. Genetic analysis also revealed deviations in almost 2% of cases when expectant mothers were over 35 years old or the results of an ultrasound examination indicated the likelihood of any problems unrelated to the structure of the fetus.

As part of a parallel study conducted under the leadership of Dr. Uma Reddy from the National Institute of Child Health and Human Development of the USA, 532 cases of intrauterine fetal death were analyzed. Genetic testing revealed the causes of 87% of cases, while the effectiveness of the method of visual analysis of chromosomes was only 70%.

Genetic abnormalities can manifest as minor defects, such as clubfoot, and more serious problems, including mental retardation, heart disease or pathologies incompatible with life. According to the researchers, it is impossible to guarantee an ideal child, however, if future parents want to do everything possible to exclude or prevent various kinds of problems, a genetic test can provide them with much more information than traditional methods of prenatal diagnosis.

Articles by Ronald J. Wapner et al. Chromosomal Microarray versus Karyotyping for Prenatal Diagnosis and Uma M. Reddy et al. Karyotype versus Microarray Testing for Genetic Abnormalities after Stillbirth is published in the New England Journal of Medicine.

Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru11.12.2012

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