While we're waiting...
So it's been 3 weeks and 1 day since the cells from our 15 blasts were sent to Reprogenetics in NJ for CGH testing. Our geneticist, a few days before my ER, informed us that it may take around 8 weeks to get the results back. So it looks like we've got a little while yet to go. I have always been very anxious during my 2 week wait, so this is having me on pins and needles for 4 times longer!
While we're waiting, let me give a quick overview of CGH (from what I understand). CGH stands for Comparative Genomic Hybridization and is used to analyze the full karyotype (23 pairs plus the sex chromosomes). It is used to identify an imbalance in chromosomal material such as Trisomy 21. It is until recently (within the past few months) that CGH can be used to screen for certain translocations (i.e., Robertsonian Translocation 13;15). We've been told that we're one of the first couples to use CGH to screen for Jerry's type of translocation. Before this, we could only do FISH analysis (tests only 9 to 12 pairs plus the sex chromosomes).
The process starts when the embryos are grown until they reach the blast stage (usually around 5 days in culture). Then the embryologist grades the embryos and decides which embryos to biopsy. The embryologist then biopsies the trophectoderm cells (outer cell mass of the embryo). The cells from each embryo are placed in its own test tube and shipped to Reprogenetics for analysis. Because the turnaround time for CGH, all of the biopsied blasts must be cryopreserved.
Once the samples are received by Reprogenetics, the DNA contained in the tubes is amplified. The sample DNA is tagged with a green fluorescent tag and then mixed with a sample of normal DNA, which is fluorescently labeled red. Then the sample DNA (green) and the normal DNA (red) are cohybridized to a slide, which takes approximately 71 hours. Then a microscopic analysis is done. The images images are collected and analyzed by the computer, which compares the intensities between the green and red of each chromosome. Thus, a molecular karyotype is generated. A 1:1 ratio of each chromosome is considered normal. Any other ratios are considered abnormal. A couple of examples of abnormal results include Trisomy 21 with a 3:2 ratio and Monosomy 21 with a 1:2 ratio. CGH has an accuracy rate of around 90%.
The chromosomes of interest to us are chromosomes 13 and 15. Those are the chromosomes affected with Jerry's Robertsonian Translocation. I will discuss the Robertsonian Translocation in further detail in another post. The reason we're doing CGH this time instead of the FISH analysis is because we've never gotten a BFP, even after transferring top quality PGD normal blasts. Remember, the FISH analysis only screens for up to 12 chromosomes. So there is a possibility that even though our previous blasts were considered PGD normal, the other chromosomes that weren't screen may be abnormal and we just didn't know it. Hopefully, CGH testing will be able to give us some much needed answers.
Posted by Linda at 8:59 AM