FISH Alternative Promising for Aneuploidy Search.

RANCHO MIRAGE, CALIF. -- A relatively new technique called comparative genomic hybridization may soon replace fluorescent in situ hybridization as the method of choice for obtaining preimplantation genetic diagnoses for aneuploidy in blastomeres.

Comparative genomic hybridization (CGH) is a molecular cytogenic technique that enables simultaneous enumeration of every chromosome, in contrast to fluorescent in situ hybridization (FISH), which at present can karyotype only a maximum of nine chromosomes, Leeanda Wilton, Ph.D., said at the annual meeting of the Pacific Coast Reproductive Society.

The technique was originally developed to look for aneuploidies in tumor cells.

In an initial analysis of CGH, Dr. Wilton, who heads the genetic and molecular research laboratory at the Melbourne (Australia) IVF clinic, reported that 51 blastomeres were karyotyped from embryos removed from nine patients with multiple recurrent in vitro fertilization (IVF) failures. Each embryo had reached the 6-month statutory limit for cryo-preservation and was no longer available for implantation.

After thawing, the blastomeres were removed on day 3. Every chromosome was normal in 20 of the 51(39%) blastomeres analyzed.

Aneuploidies were detected in 31 blastomeres; 9 involved one chromosome, and 8 involved two chromosomes, Of the remaining blastomeres, almost half showed extensive aneuploidies of at least three chromosomes, Dr. Wilton noted.

By comparison, if FISH had been used to karyotype the same blastomeres, 69% of the aneuploidies would have been missed using the 5-chromosome technique, and 58% would have gone undetected using the 9-chromosome method.