"Duchenne and Becker muscular dystrophy, Prader-Willi syndrome, and Williams syndrome are some of the disorders believed to result from microdeletions. FISH methods can also detect copy-number variations that underlie a range of other genetic diseases.
FISH methods use nucleotide probes that hybridize with target sequences, tagged with a fluorescent molecule so that successful binding can be visualized under a microscope.
For detecting microdeletions in a particular gene, the probe is designed to bind its normal sequence. An absent fluorescent signal indicates that hybridization failed, meaning the gene is missing or defective.
FISH is a standard laboratory tool for cytogenetic analysis, but its adaptation to in vitro fertilization (IVF) embryo analysis is relatively untested, in part because it must be made to work on one or two cells.
In the current study, Dr. Vermeesch and colleagues used the technique on embryos from three couples having a total of seven IVF cycles. The women in these couples were known carriers of microdeletions related to neurofibromatosis type 1 or Von Hippel-Landau disease.
The researchers biopsied 64 embryos produced from these cycles. Two blastomeres with excised from each embryo for analysis. Although it would have been possible to perform the tests on single blastomeres, Dr. Vermeesch and colleagues believed analyzing two would be more accurate.
Incomplete results were obtained for 14 embryos and were excluded. The FISH procedure failed in one case, and only one blastomere could be analyzed in 13.
Of the 50 embryos successfully analyzed, 17 appeared normal and healthy. Deletions related to neurofibromatosis type 1 or Von Hippel-Landau disease were found in 27 embryos. The remaining embryos were mosaic or had other abnormalities such as copy-number variations.
Ten embryos were implanted in the women, two of which resulted in pregnancy -- twins born to one woman, with both infants found to be free of microdeletions.
Dr. Vermeesch and colleagues called the approach a success, but suggested it would be more practical when it can be implemented on an array platform. This technology would allow many different analyses for microdeletions and other mutations to be performed simultaneously."
The obvious ethical question is whether or not parents would abort the child if they discovered she had WS.