A confirmatory test from Trisomies
Screening for Down’s syndrome is offered routinely to thousands of women each year as part of standard antenatal care. Confirmatory testing of samples positive for the first trimester screen or Harmony screens is required once detected. For those women identified as being at high risk of carrying a Down syndrome fetus, chorionic villus sampling (taken at 10-12 weeks) or amniocentesis (taken at 12-16 weeks) is the sample required for confirmation.
Quantitative Fluorescence PCR
This test offered by Carigen utilizes the QF-PCR (Quantitative fluorescence- Polymerase Chain Reaction) technique. Using a technique called PCR amplification, fluorescent labelled dye labelled DNA are able to make more copies of the fetal DNA present and determine how many chromosomes there are at each marker being studied.
The QSTR plus screen assesses markers for chromosomes 13, 18, 21, X and Y and will detect both the most common Trisomies and sex chromosome aneuploidies in a single test.
Our QSTR markers are used to detect the three most common trisomies:
- Trisomy 21 (Down syndrome)
- Trisomy 18 (Edwards syndrome)
- Trisomy 13 (Patau syndrome)
Sexual abnormalities
Additional markers on the sex chromosomes X and Y can detect the most common sex chromosome aneuploidies. Our QST*R-XY systems detect DNA sequences on both the X and Y chromosome. It can be used to detect sex chromosome aneuploidies including Turner syndrome (monosomy X) and Klinefelter syndrome (47, XXY)
The technology
Standard cytogenetic techniques involving tissue culture and microscopic analysis can take up to 14 days to provide a diagnosis. Fluorescent in-situ Hybridisation (FISH) using interphase cells is expensive, time consuming and unsuitable for high throughput use.
The QF-PCR (Quantitative fluorescence- Polymerase Chain Reaction) technique. primers target highly polymorphic regions of DNA sequence, short tandem repeats (STRs) that are located on the chromosomes of interest. Each targeted STR marker is specific to the chromosome on which it is located, thus the copy number of the STR marker can be diagnostic of the copy number of the chromosome.
A normal sample has the normal complement of two of each of the autosomal chromosomes and two sex chromosomes, thus two alleles of a chromosome specific STR are determined by the QF-PCR technique as two peaks in a 1:1 ratio. The observation of an extra STR allele as either a three peak pattern in a 1:1:1 ratio or two peak pattern in a 2:1 peak ratio is diagnostic of the presence of an additional sequence which in turn may represent an additional chromosome, as in the case of a trisomy.
Validated for Diagnostic use
This series of tests have been fully validated for in vitro diagnostic use and suitable for both chorionic villus and amniotic fluid analysis. Studies have shown a greater than 99% concordance with standard karyotyping. The testing may be used as a preliminary test before karyotyping or for final analysis.
The turnaround time for this test is three to five business days.
