IVDT_In Vitro Diagnostics Technology

IVD Technology, Spring 2013

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First-generation approaches to noninvasive Prenatal Testing Te frst generation of tests to hit the market, from Sequenom, Verinata and Ariosa, are all based on a counting approach.6, 9-15 Tese methods enable noninvasive detection of autosomal and some sex chromosome aneuploidies, a signifcant advance over the less-reliable blood-based hormone screening tests. Tese tests have shown that they are able to signifcantly reduce the number of unnecessary invasive procedures performed. However, these methods have limitations when detecting abnormities beyond trisomy 21 and 18, limiting their ability to detect, with high accuracy, the full scope of abnormalities that can be detected by amniocentesis or chorionic villus sampling (CVS). Te counting approach involves PCR amplifcation and detection of the cell-free DNA by massively parallel shotgun sequencing9, 15 or targeted sequencing.11 Te number of DNA sequences detected from the target chromosome is counted and compared to the number from a reference chromosome that is presumed to be euploid. If the ratio of the number of sequences from the target chromosome and the reference chromosome is as expected, then the fetus is presumed to be euploid. However, if the proportion of DNA sequences from the target chromosome is increased and exceeds a threshold, then fetal trisomy is inferred. While counting approaches can accurately detect trisomy 21 and trisomy 18 given a sufcient fetal cell-free DNA fraction, they are less successful at consistently detecting trisomy 13 and sex chromosome abnormalities. Specifcally, the requirement for a reference chromosome means that the counting methods are all afected by amplifcation variation. Tat is, certain chromosomes amplify inconsistently, leading to variability in the ratio used to detect aneuploidy that is of an equivalent magnitude as the signal caused ivd tech n o lo gy.com magenta cyan yellow black by the abnormal fetal chromosome, thus resulting in miscalls.9, 10, 16 Tis is clearly not ideal for a screening test that requires reliability. Additionally, the signal from the abnormal fetal chromosome is directly proportional to the fraction of fetal cell-free DNA that is present in the maternal plasma. Tis fetal fraction typically varies from 3% to No Toxic Preservatives 40%, and averages between 10% and 15% between 10 and 20 weeks gestation when most women present to their doctor.9-11, 15-18 Fetal fractions below 8%, which are found in about a quarter of these pregnancies,17, 18 greatly afect the accuracy of this approach, reducing the detection rate to 75% at these levels.9 In addition, the counting methods cannot Premium Substrates, Buffers & Stabilizers Industry Market Leader No Harmful Organic Solvents Decrease Assay Time No BSA Increase Detection Limits No Hazardous Stop Solutions Eliminate Wash Steps & Reduce Water Waste Prolong Shelf Life www.kem-en-tec.com K e m - E n - T e c U S A x W i n d s o r , C T 0 6 0 9 5 x 8 6 0 -2 9 8 - 0 2 3 4 kementecusa@rainbowscientific.com ZĂŝŶďŽǁ^ĐŝĞŶƚŝĨŝĐ /ŶĐ <Ğŵ -Ŷ-dĞĐh^ŝǀŝƐŝŽŶ ဒϯDĂƉůĞǀĞ tŝŶĚƐŽƌ dϬϲϬ ϱ ဒϲϬ -Ϯ ဒ-ϬϮϯϰ I VD T EC H N O LO G Y | S PR I NG 2 0 1 3 3 5 ES235876_IV1305_035.pgs 04.23.2013 05:10 UBM

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