Human Reproduction, Vol. 17, No. 12, 3037-3038,
December 2002
© 2002 European Society of Human Reproduction and Embryology
Dispermy—origin of diandric triploidy
Brief Communication
Departments of Pathology and Medical Genetics, Children’s and Women’s Hospital of B.C. and University of British Columbia, Vancouver, B.C. V6H 3V4, Canada
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Abstract |
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Triploidy may arise from either digynic or diandric fertilizations. Errors in the second meiotic division account for most digynic triploidy while most studies have found that
2/3 of diandric triploids arise as the result of dispermy and 1/3 as the result of meiotic errors giving rise to diploid sperm. Using molecular markers very close to the centromere, all 14 cases of diandric triploidy were shown to be the result of dispermy with no evidence to support a meiotic error as the origin of diandric triploids.
Key words: diandry/dispermy/triploidy
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Introduction |
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TopAbstractIntroductionMaterials and methodsResults and discussionAcknowledgementsReferences |
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Triploidy, the presence of an extra haploid set of chromosomes, occurs in 6% of spontaneous abortions. There are a number of theoretical mechanisms by which triploidy may arise. Triploidy is the result of an extra haploid set of chromosome that may be maternal (digynic) or paternal (diandric) in origin. Although diandry was once thought to account for >80% of triploidy, more recent studies demonstrate that digyny is responsible for more cases of triploidy than previously thought (McFadden et al., 1993
; Miny et al., 1995; Baumer et al., 2000; McFadden and Langlois, 2000). Digyny predominates amongst the fetal and infant periods. Diandry accounts for ~50–65% of early triploid spontaneous abortion (SA), [95% confidence interval (CI) for proportion of diandry in SA: 28–65% in McFadden and Langlois, 2000 and 50–74% in Zaragoza et al., 2000] (Redline et al., 1998; McFadden et al., 2000; Zaragoza et al., 2000).
Digynic triploidy may be the result of fertilization of a diploid ovum by a single sperm, with the diploid ovum being the result of either an error in the first (MI) or second (MII) meiotic division. Diandry may be the result of fertilization of a normal ovum by either a diploid sperm (MI or MII error) or by two sperm (dispermy). In previously reported series, MII errors have been estimated to account for 50–75% of digynic triploidy, regardless of the gestational age or stage of the pregnancy (Baumer et al., 2000; McFadden and Langlois, 2000; Zaragoza et al., 2000).
In early studies using chromosomal heteromorphisms, dispermy had been reported to account for 65% of all diandric triploidy and 35% were thought to be the result of either dispermy or fertilization of an ovum by a diploid sperm arising from MI error (Jacobs et al., 1978). More recent studies using molecular markers have estimated that dispermy accounts for 86% (37/43 cases) of diandric early SA. The remaining diandric cases appeared to be the result of fertilization of ova by diploid sperm, with diploid sperm arising as the result of MI error in 4/43 cases and MII error in one case (Zaragoza et al., 2000).
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Materials and methods |
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TopAbstractIntroductionMaterials and methodsResults and discussionAcknowledgementsReferences |
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To establish the mechanism of diandric triploidy, we examined 14 diandric triploids (fetuses, infants, and SA) in which parental origin had been determined but no assignment made as to the mechanism responsible (McFadden and Langlois, 2000
). In all cases, fetal, maternal, and paternal DNA were available for analysis. We used microsatellite markers in addition to those used to establish parental origin and availed of more recent mapping data to ensure closeness (<1.5 cM (centimorgan) to the centromere (http://cedar.genetics.soton.ac.uk/pub) and, for some chromosomes, used markers flanking the centromere on both arms. Diploid sperm as the result of an MI error should show non-reduction at all centromeres for which the father is heterozygous and those arising from errors in MII should show reduction to homozygosity at all centromeres. Dispermy should have random assortment of chromosomes. We used pericentromeric markers and interpreted the findings as being consistent with dispermy when there was reduction to homozygosity at the centromere for two markers with non-reduction at two other centromeres. |
Results and discussion |
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TopAbstractIntroductionMaterials and methodsResults and discussionAcknowledgementsReferences |
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For each case, there are pericentromeric markers that are reduced to homozygosity and those that are non-reduced (Table I
). In all cases, the sex chromosome complement provided evidence of mechanism in conjunction with pericentromeric markers from other chromosomes. In cases in which the informative marker was >1.0 cM from the centromere but <1.5 cM, informative markers on either side of the centromere were taken as conclusive evidence of the reduced/non-reduced status as it is unlikely that a double crossover would occur in such a small area around a centromere e.g. cases 4 and 12. In all 14 cases, the results are consistent with dispermy as the mechanism for diandric triploidy. The 95% CI on the estimated proportion of dispermy was 78–100%. In reviewing the cases in the literature, it is important to note that many of the cases reported as being due to diploid sperm were either based on interpretation of centromeric heteromorphisms (Jacobs et al., 1978) or on origin assigned through a likelihood approach in cases in which paternal DNA was not available (Zaragoza et al., 2000).
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No case in which paternal DNA was available for testing has shown evidence of diploid sperm. We suggest that while 0.3% of sperm are estimated to be diploid by fluorescence in-situ hybridization (FISH) (Shi and Martin, 2000
), these sperm rarely, if ever, successfully fertilize an ovum. Thus, virtually all triploidy is a consequence of an error in the ovum: either a division error leading to digyny or an abnormality of the ovum that fails to block fertilization by more than one sperm.
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Acknowledgements |
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TopAbstractIntroductionMaterials and methodsResults and discussionAcknowledgementsReferences |
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This research was supported by Canadian Institutes of Health Research grant #78312 (W.P.R.).
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Notes |
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1 To whom correspondence should be addressed. E-mail: dmcfadden{at}cw.bc.ca
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References |
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TopAbstractIntroductionMaterials and methodsResults and discussionAcknowledgementsReferences |
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Baumer, A., Balmer, D., Binkert, F. and Schinzel, A. (2000) Parental origin and mechanisms of formation of triploidy: a study of 25 cases. Eur. J. Hum. Genet., 8, 911–917.[ISI][Medline]
Jacobs, P.A., Angell, R.R., Buchanan, I.M., Hassold, T.J., Matsuyama, A.M. and Manuel, B. (1978) The origin of human triploids. Ann. Hum. Genet., 42, 49–57.[ISI][Medline]
McFadden, D.E. and Langlois, S. (2000) Parental and meiotic origin of triploidy in the embryonic and fetal periods. Clin. Genet., 58, 192–200.[ISI][Medline]
McFadden, D.E., Kwong, L.C., Yam, I.Y.L. and Langlois, S. (1993) Parental origin of triploidy in human fetuses: evidence for genomic imprinting. Hum. Genet., 92, 465–469.[ISI][Medline]
Miny, P., Koppers, B., Dworniczak, B., Bogdanova, N., Holzgreve, W., Tercanli, S., Basaran, S., Rehder, H., Exeler, R. and Horst, J. (1995) Parental origin of extra haploid set in triploidies diagnosed prenatally. Am. J. Med. Genet., 57, 102–106.[ISI][Medline]
Redline, R.W., Hassold, T. and Zaragoza, M.V. (1998) Prevalance of the partial molar phenotype in triploidy of maternal and paternal origin. Hum. Pathol., 29, 505–511.[Medline]
Shi, Q. and Martin, R.H. (2000) Spontaneous frequencies of aneuploid and diploid sperm in 10 normal Chinese men: assessed by multicolor fluorescence in situ hybridization. Cytogenet. Cell Genet., 90, 79–83.[Medline]
Zaragoza, M.V., Surt, U., Redline, R.W., Millie, E., Chakravarti, A. and Hassold, T.J. (2000) Parental origin and phenotype of triploidy in spontaneous abortions: predominance of diandry and association with the partial hydatidiform mole. Am. J. Hum. Genet., 66, 1807–1820.[ISI][Medline]
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