Reply: Different perceptions of similar observations

Reply: Different perceptions of similar observations Reply of the Authors: We appreciate the interest Briton-Jones et al. showed in our paper (1). We agree that “micronucleus extrusion” frequently is irregular and often contains fragments of chromosomes, seemingly at random. From the thousands of images we have of fixed blastomere nuclei, most do in fact display irregular extruded fragments containing a variety of different chromosomes. As it happens, we selected a symmetrical image to be used in our publication. It does not mean all the “extrusions” appear as this example, one that also happens to contain a haploid set of chromosomes. Polar bodies (PBs), especially second ones, degenerate soon after they are extruded (2). It is possible, but not very likely, that the nucleus of the second PB, sperm heads (with no tail), or other contaminating aneuploid cells successfully make it through several washing steps after being inadvertently cobiopsied and fixed intact at very close proximity to the nucleus of a day 3 blastomere by Carnoy’s fixative flush without being noticed by the technicians. People who perform this work know how low the frequency of such an occurrence is—this is why it is considered acceptable to perform routine insemination with IVFET/PGD–aneuploidy screening because artifacts such as those described by the authors are readily recognized and their relevance is discounted.

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The dynamics of the process of mitosis remains an active subject of investigation, and while much is known of this process, much is still unclear. We are not suggesting by our research to “own” the hypothesis that embryonic cells can sequester extranumeric chromosomes. Actually, trisomic rescues of chromosomes for uniparental disomy (3, 4) are welldocumented examples of this hypothesis. Man Li, M.D., PhD ART Reproductive Center Beverly Hills, California January 1, 2006

REFERENCES 1. Li M, DeUgarte CM, Surrey M, Danzer H, DeCherney A, Hill D. Fluorescence in situ hybridization reanalysis of day-6 human blastocysts diagnosed with aneuploidy on day 3. Fertil Steril 2005;84:1395–1400. 2. Wakayama T, Yanagimachi R. The first polar body can be used for the production of normal offspring in mice. Biol Reprod 1998;59:100 –104. 3. Los FJ, Van Opstal D, Van den Berg C, Braat APG, Verhoef S, Wesby-van Swaay E, et al. Uniparental disomy with and without confirmed placental mosaicism: a model for trisomic zygote rescue. Prenat Diagn 1998;18:659 – 68. 4. Elias ER, Tsai ACH, Manchester DK. Genetics and dysmorphology In: Hay WW, Levin MJ, Sondheimer JM, Deterding RR, eds. Current pediatric diagnosis and treatment. 17th ed. New York, Chicago, San Francisco: McGraw-Hill Publishers, Inc., 2005; chap. 33, pp. 1039 –78.

doi:10.1016/j.fertnstert.2006.01.002

Fertility and Sterility姞 Vol. 85, No. 4, April 2006 Copyright ©2006 American Society for Reproductive Medicine, Published by Elsevier Inc.

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