Preimplantation genetic diagnosis (PGD) is currently used to screen embryos for common chromosomal abnormalities such as aneuploidy, facilitating the implantation of only normal embryos to achieve better outcomes during assisted reproduction. Now, a recent study published in the journal Fertility and Sterility identifies three-dimensional fluorescence in situ hybridization (3D-FISH) as a feasible and efficient method for PGD, as it causes minimal damage to blastomeres and eliminates the loss of blastomeres during fixation.
Li-Ying Yan, a lead scientist from Peking University Third Hospital, Beijing, People’s Republic of China, and coworkers, conducted the study on women undergoing IVF or intracytoplasmic sperm injection (ICSI) to determine the efficacy of 3D-FISH for PGD. Outcome measures considered were the intensity and clarity of signals, technical difficulties, the percentage of blastomeres successfully treated, and integrity of blastomeres following FISH. The paraformaldehyde fixation technique was used on 35 blastomeres derived from 10 arrested embryos or abnormally fertilized eggs, to obtain signals for diagnosis. It was found that in each blastomere, 0.1 μL of DNA probe was sufficient for the detection of the signals, which is lesser than the volume used (1 μL) in conventional FISH technique. The scientists suggested that more patients may benefit from this method since the technique is efficient, economical and causes less damage to blastomeres.
Preimplantation genetic diagnosis has been used to improve IVF outcome in patients who have failed 3 or more IVF attempts. In an earlier study, Pehlivan, et al. (Reproductive Biomed Online, 2003) carried out PGD in 49 study subjects with a mean number of 4.2 +/- 1.6 IVF failures previously, and 9 fertile controls. For chromosomes 13, 16, 18, 21, 22, X and Y, FISH was performed on blastomeres obtained from biopsied day-3 embryo. Chromosomal abnormalities were found in 67.4% of the test group in comparison to 36.3% of the controls. In 57 cycles, implantation failure patients had a 34% pregnancy rate and 19.8% implantation rate as opposed to 33.3% and 24.1% in controls. It was also seen that all the pregnancies in the test group were due to the transfer of at least one chromosomally normal blastocyst on day 5. Hence, it was concluded that the PGD use with blastocyst transfer improved the IVF treatment outcome.
Fluorescence in situ hybridization (FISH), a molecular cytogenetic technique, employs fluorescent labeled DNA probes for the detection of genes and chromosomal abnormalities. The probes tagged with either fluorescent antibodies corresponding to the antigen incorporated or by fluorescent avidin molecules, hybridize specifically to complementary DNA and help in the identification of target sequences.
FISH aids in the diagnosis of diseases such as chronic myelogenous leukemia, chronic lymphocytic leukemia, acute lymphoblastic leukemia, Down syndrome, Angelman syndrome, and other genetic disorders. Apart from the above-mentioned applications, the technique is also used for the detection of minimal residual disease, monitoring of therapeutic effects, and cell origin following bone marrow transplantation.
The past decade has witnessed the emergence of several new techniques supplementing the preimplantation genetic diagnosis. The current study, demonstrating the efficacy of 3D-FISH in augmenting diagnostic pre-pregnancy option, could also be an effective alternative for currently used postconception diagnostic procedures.
References
1. Yan LY, Qiao J, Chen Y, Huang J, Liu P, Sun QY. Application of three-dimensional fluorescence in situ hybridization to human preimplantation genetic diagnosis. Fertil Steril. 2008 Nov 4. [Epub ahead of print].
2. Pehlivan T, Rubio C, Rodrigo L, et al. Impact of preimplantation genetic diagnosis on IVF outcome in implantation failure patients. Reprod Biomed Online. 2003 Mar;6(2):232-7.
