Parental origin of triploidy in human fetuses: evidence for genomic imprinting

Polyploid incidence and evolution

Changes in ploidy occurred early in the diversification of some animal and plant lineages and represent an ongoing phenomenon in others. While the prevalence of polyploid lineages indicates that this phenomenon is a common and successful evolutionary transition, whether polyploidization itself has a significant effect on patterns and rates of diversification remains an open question. Here we review evidence for the creative role of polyploidy in evolution. We present new estimates for the incidence of polyploidy in ferns and flowering plants based on a simple model describing transitions between odd and even base chromosome numbers. These new estimates indicate that ploidy changes may represent from 2 to 4% of speciation events in flowering plants and 7% in ferns. Speciation via polyploidy is likely to be one of the more predominant modes of sympatric speciation in plants, owing to its potentially broad-scale effects on gene regulation and developmental processes, effects that can produce immediate shifts in morphology, breeding system, and ecological tolerances. Theoretical models support the potential for increased adaptability in polyploid lineages. The evidence suggests that polyploidization can produce shifts in genetic systems and phenotypes that have the potential to result in increased evolutionary diversification, yet conclusive evidence that polyploidy has changed rates and patterns of diversification remains elusive.

Gonadal pathology in triploidy

There are numerous reports describing the pathology of the fetus and placenta in triploidy. Although gonadal pathology is described in many of these reports, consistent changes have not been noted nor is it clear whether genital ambiguity can be considered part of the triploid phenotype. We present a case of triploidy of probable diandric origin, in which there were dysgenetic gonads with abnormal seminiferous tubules, nodules of undifferentiated stroma, and focal absence of the tunica albuginea. As this finding was distinctly unusual in our experience of triploid gonadal pathology, we reviewed the gonadal histology in 51 fetal and infant triploids examined in our autopsy/embryopathology laboratory. The gonads were compared to age-matched normal controls to determine if there was a specific gonadal pathology associated with triploidy and if there was any correlation of this pathology with parental origin of the triploidy. Our review of the triploid gonads indicated that while minor, nonspecific changes were not uncommon, overtly dysgenetic gonads, as observed in the index case, are rare.

Genetic aspects of miscarriage

Fetal chromosome abnormalities account for about 50% of first-trimester pregnancy losses. Most of these abnormalities are numerical abnormalities (86%) and a low percentage is caused by structural abnormalities (6%) or other genetic mechanisms, including chromosome mosaicism (8%). The recurrence risk of numerical abnormalities is low, so karyotyping of fetal material in case of a miscarriage does not seem worthwhile in daily practice. Half of the structural abnormalities may be inherited from a parent carrying a balanced chromosome translocation or inversion. Parental carriership is found in 4-6% of the couples with recurrent miscarriage. In case of parental carriership of a balanced structural chromosome abnormality, a next pregnancy may result in a child with an unbalanced structural chromosome abnormality. This child can have multiple congenital malformations and/or a mental handicap. Prenatal diagnosis is therefore recommended. Conventional laboratory techniques, such as tissue culturing and karyotyping, or (semi-)direct chromosome technique of chorionic villi, and the recently developed laboratory techniques such as fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH), are described successively. Until now, not enough evidence has been available about the role of other genetic mechanisms, such as single-gene abnormalities, uniparental disomy, genomic imprinting, multifactorial disorders and skewed X chromosome, in the occurrence of miscarriages.

Parental and meiotic origin of triploidy in the embryonic and fetal periods

Triploidy is a common finding both in early spontaneous abortions and in the fetal period. Previous studies suggested that the majority of triploidy was the result of diandry, specifically dispermy. Molecular determination of parental origin in fetal triploids has shown that digyny accounts for the majority of triploids in the fetal period. The aim of this study was to determine the meiotic level at which the error leading to digynic triploidy occurs and to extend the molecular analysis of parental origin of triploidy into the embryonic period. Maternal age of digynic triploids was compared with that of the diandric cases. Using polymorphic pericentromeric markers, we have shown that the majority of digynic triploidy is the result of errors in the second meiotic division. Digyny accounted for the majority of triploids, even in the nonfetal cases. Diandry predominated in a subset of the non-fetal cases in which embryos were not present and in which the placental findings of partial hydatidiform mole (PHM) were encountered. Maternal age differed between the digynic and diandric groups only for the non-fetal cases; this was attributed to differences in ascertainment.

Genetic control of intra-uterine growth

The expression of a few genes in the human genome depends on whether they are located on the maternal or on the paternal chromosome. This phenomenon is called genomic imprinting. Several of these genes have a role in normal embryonic and fetal growth, as indicated by an abnormal development associated with disturbed genomic imprinting. This has lead to the suggestion that the genomic imprinting has evolved as a mechanism to regulate embryonic and fetal growth.

Screening for triploidy by fetal nuchal translucency and maternal serum free beta-hCG and PAPP-A at 10-14 weeks of gestation

In 25 cases of triploidy at 10-14 weeks of gestation, compared with 947 controls, the median multiple of the median (MoM) fetal nuchal translucency (NT) thickness was significantly increased (1.89 MoM), and maternal serum total and free beta-human chorionic gonadotrophin (hCG) were increased (3.13 MoM and 4.59 MoM respectively), alpha fetoprotein (AFP) was increased (2.14 MoM), and pregnancy associated plasma protein A (PAPP-A) was decreased (0.12 MoM). There are two types of triploidy. In type I, where the additional chromosome set is of paternal origin, the placenta is partially molar and the fetus is relatively well-grown. Type II, where the extra chromosome set is of maternal origin, is characterized by a small normal looking placenta and severe asymmetrical fetal growth restriction. In type I triploidy there was increased fetal NT (2.76 MoM), maternal serum total hCG (4.91 MoM), free beta-hCG (8.04 MoM), and AFP (3.22 MoM), and mildly decreased PAPP-A (0.75 MoM). In type II triploidy fetal NT was not increased (0.88 MoM), and there was a decrease in maternal serum total hCG (0.16 MoM), free beta-hCG (0.18 MoM), PAPP-A (0.06 MoM) and AFP (0.77 MoM). We conclude that a large proportion of triploidy cases of both phenotypes could be identified in the first trimester using NT, maternal serum free beta-hCG and PAPP-A with a combination of trisomy 21 risk and an atypicality approach.

Parental origin and phenotype of triploidy in spontaneous abortions: predominance of diandry and association with the partial hydatidiform mole

The origin of human triploidy is controversial. Early cytogenetic studies found the majority of cases to be paternal in origin; however, recent molecular analyses have challenged these findings, suggesting that digynic triploidy is the most common source of triploidy. To resolve this dispute, we examined 91 cases of human triploid spontaneous abortions to (1) determine the mechanism of origin of the additional haploid set, and (2) assess the effect of origin on the phenotype of the conceptus. Our results indicate that the majority of cases were diandric in origin because of dispermy, whereas the maternally-derived cases mainly originated through errors in meiosis II. Furthermore, our results indicate a complex relationship between phenotype and parental origin: paternally-derived cases predominate among "typical" spontaneous abortions, whereas maternally-derived cases are associated with either early embryonic demise or with relatively late demise involving a well-formed fetus. As the cytogenetic studies relied on analyses of the former type of material and the molecular studies on the latter sources, the discrepancies between the data sets are explained by differences in ascertainment. In studies correlating the origin of the extra haploid set with histological phenotype, we observed an association between paternal-but not maternal-triploidy and the development of partial hydatidiform moles. However, only a proportion of paternally derived cases developed a partial molar phenotype, indicating that the mere presence of two paternal genomes is not sufficient for molar development.

Digynic triploid infant surviving for 46 days

We report on a triploid infant who survived for 46 days. She had severe intrauterine growth retardation, relative macrocephaly, and a small, noncystic placenta, which are manifestations compatible with type II phenotype. Cultured amniotic fluid cells, skin fibroblasts, cord blood, and peripheral blood lymphocytes all showed a nonmosaic 69,XXX karyotype. Analysis of chromosomal heteromorphisms and microsatellite DNA polymorphisms in the infant and her parents indicated that the extra haploid set in the infant resulted from nondisjunction at maternal second meiosis. Postzygotic, mitotic nondisjunction was ruled out because of the presence of both homozygous and heterozygous markers of maternal origin. A search of the literature demonstrated five triploid infants, including the girl we described, who survived 4 weeks or more, and the parental origin of whose triploidy was studied: four were digynic and one was diandric. These findings support the notion that type II triploids are digynic in parental origin and that they survive longer than type I, diandric triploids.

Parthenogenetic activation of marmoset (Callithrix jacchus) oocytes and the development of marmoset parthenogenones in vitro and in vivo

Mammalian oocytes can be induced to resume meiosis without fertilization, and the resulting parthenogenetic embryos carry only maternal chromosomes. Human oocytes can be activated by many chemical and physical stimuli, but postimplantation studies of human parthenogenetic embryos are not ethically acceptable. The common marmoset monkey (Callithrix jacchus) is a good model for studying primate parthenogenetic development postimplantation, since follicular aspiration, embryo transfer, and early postimplantation development of biparental embryos have already been described. Marmoset oocytes were either subjected to two series of six electrical pulses (DC; 2 kV/cm and 70 microsec) or were incubated in 7% ethanol in PBS. Ninety-two percent (68 of 74) and 20% (8 of 40) of marmoset oocytes were activated by electrical stimulus or ethanol, respectively. Parthenogenetic (n = 3) or in vitro-fertilized (n = 2) embryos were transferred at the 4-cell stage to synchronized recipient female marmosets (n = 5). Progesterone, chorionic gonadotropin, and inhibin in the peripheral plasma of recipient animals were measured. After 33 days of gestation, recipient animals were perfused and the uteri were collected. The 2 females that had received biparental embryos and 2 of the 3 females that had received parthenogenetic embryos displayed biochemical and histological evidence of implantation. This is the first report that a primate embryo comprising only parthenogenetic cells is capable of implantation. This highlights the need to scrutinize levels of parthenogenesis associated with human assisted reproductive technologies. Marmoset parthenogenones also provide a unique model for elucidating the roles of parental genomes in primate development.

Studies of non-disjunction in trisomies 2, 7, 15, and 22: does the parental origin of trisomy influence placental morphology?

Recently, there have been several molecular studies of trisomic fetuses and liveborns which have examined the parent and meiotic stage of origin of nondisjunction. However, little is known about the possible phenotypic effects of the origin of trisomy. For trisomic spontaneous abortions, no distinct phenotype has been described, although some have been reported to have features, such as trophoblastic hyperplasia, similar to hydatidiform moles. In the present report, we describe molecular and histological studies of spontaneous abortions with trisomies 2, 7, 15, or 22, conditions occasionally linked to trophoblastic hyperplasia. Our results provide strong evidence for chromosome specific mechanisms of nondisjunction, with trisomy 2 having a high frequency of paternally derived cases and trisomy 7 typically originating postzygotically. In studies correlating parental origin of trisomy with phenotype, we found no difference in the proportion of cases with trophoblastic hyperplasia, fetal tissue, nucleated red blood cells, or hydropic villi among paternally or maternally derived trisomies 2, 7, 15, or 22. However, paternally derived trisomies tended to abort earlier than maternally derived trisomies. This suggests that parental origin might affect the developmental stage at which abortion occurs but not other features of placental phenotype.

Genomic imprinting in testicular germ cell tumours

Genomic imprinting refers to the parental origin-specific functional difference between the paternally and maternally-derived mammalian haploid genome. Normal embryogenesis depends on the presence of both a paternal and a maternal copy of particular chromosomal regions, containing the so-called imprinted genes. Genomic imprinting is established somewhere in the maturation from a primordial germ cell to a mature gamete, either spermatid or oocyte. We discuss the value of testicular cancers, especially those derived from the germ cell lineage, as a model to study erasement of the biparental pattern of genomic imprinting as present in the zygote and establishment of the paternal pattern during spermatogenesis. In addition, we will present data on the presence of X-inactivation in these cancers.

Chromosome abnormalities in human beings

Constitutional chromosomal abnormalities are an important cause of miscarriage, infertility, congenital anomalies and mental retardation in humans. Most human constitutional chromosomal imbalance results from aneuploidy, a condition that appears to be much more frequent in humans than in any other species studied. Chromosomal rearrangements and segmental deletions and duplications also occur in humans, but much less often. Although treatment of human somatic cells with some environmental agents produces chromosomal damage, no measurable increase in the frequency of constitutional chromosomal abnormalities has been unequivocally demonstrated among the children of parents exposed to any agent. Recent work has provided insight into a variety of mechanisms by which chromosomal abnormalities can arise during gametogenesis and early embryogenesis. Mechanisms have also been recognized that can correct or partially compensate for chromosomal imbalance, sometimes permitting survival of conceptuses that would otherwise be lost early in gestation. This improved understanding can be used to refine future studies of the cytogenetic effects of environmental exposures.

The role of deoxyribonucleic acid image cytometric and interphase cytogenetic analyses in the differential diagnosis, prognosis, and clinical follow-up of hydatidiform moles. A report from the Central Molar Registration in The Netherlands

OBJECTIVES

To assess the value of deoxyribonucleic acid ploidy in the differential diagnosis and clinical follow-up of hydatidiform moles, the histopathologic features, deoxyribonucleic acid ploidy, and clinical follow-up were compared in 347 cases: 143 complete moles, 52 partial moles, and 152 abortions, of which 56 cases were hydropic abortions with histologic features of triploidy but lacked trophoblastic hyperplasia.

STUDY DESIGN

In all cases deoxyribonucleic acid image cytometry was performed, and in 85 of these cases interphase cytogenetics was also performed.

RESULTS

With use of deoxyribonucleic acid image cytometry and interphase cytogenetics, a bimodal polyploid deoxyribonucleic acid pattern was present in 97% of complete moles, 27% of partial moles, and 4% of abortions. All these cases of partial mole were reclassified to complete mole on the basis of this deoxyribonucleic acid pattern and the histopathologic features in spite of the presence of fetal blood cells, amnion, or yolk sac. Deoxyribonucleic acid triploidy was found in 95% of the remaining partial moles, in 77% of hydropic abortions with histologic features of triploidy, and in 14% of the remaining abortions. Reliable differentiation between deoxyribonucleic acid triploid partial moles and hydropic abortions with histologic features of triploidy was not possible on basis of the histopathologic features (trophoblastic hyperplasia) or 3.5c exceeding rates. Deoxyribonucleic acid diploidy was found in 1% of complete moles, 23% of hydropic abortions with features of triploidy, and 78% of the remaining abortions. Deoxyribonucleic acid tetraploidy was rarely found (1% of complete moles, 2% of partial moles, 1% of abortions). Persistent gestational trophoblastic disease developed in 33% of the bimodal deoxyribonucleic acid polyploid cases (all complete moles), in 1% of the diploid cases (concerning one of the two diploid complete moles), and in 1% of the triploid cases (partial moles).

CONCLUSION

Deoxyribonucleic acid analysis is essential in the diagnosis of hydatidiform moles to decide on clinical follow-up.

Early prenatal diagnosis of triploidy

OBJECTIVE

Our purpose was to investigate the role of ultrasonography and maternal serum human chorionic gonadotropin in the early prenatal diagnosis of triploid pregnancies.

STUDY DESIGN

A retrospective study on 61,314 consecutive singleton pregnancies examined by ultrasonography at 10 to 14 weeks' gestation was performed to identify the prenatal features of those complicated by triploidy. When available, the serum human chorionic gonadotropin level was measured and ascertained retrospectively. Cases lost to follow-up or for which no karyotype was available were excluded from the final analysis.

RESULTS

Overall there were 18 cases of triploidy identified in a population of 58,862 singleton pregnancies, giving a prevalence of 1 in 3270. Fetal defects were observed in 8 (44.4%) of these cases; these included holoprosencephaly (n = 4), exomphalos (n = 3), and posterior fossa cyst (n = 1). In 6 (33.3%) cases the placenta showed molar changes. The fetal crown-rump length was below the 5th percentile in 10 of the 16 (62.5%) cases for which the menstrual age was also available. Fetal nuchal translucency thickness was above the 95th percentile in 12 (66.7%) cases, and the fetal heart rate was below the 5th percentile in 4 of the 13 (30.8%) cases evaluated. The maternal human chorionic gonadotropin level was high in 11 of the 13 (84.6%) cases tested, with similar distribution of the high values in molar and nonmolar triploidies.

CONCLUSION

The combination of ultrasonographic examination of the fetoplacental features and measurement of the maternal serum level of human chorionic gonadotropin enables the diagnosis of most cases of triploidy at 10 to 14 weeks' gestation.

Placental pathology of triploidy

Triploidy is a common chromosome abnormality in spontaneous abortions. Previous studies of spontaneous abortions have suggested that approximately 85% of triploid abortuses show the placental changes of partial hydatidiform mole (PHM) and that this appearance was associated, possibly attributable, to paternal origin of the extra haploid set of chromosomes. More recent work, however, has shown that most triploidy is the result of digyny--the extra set of chromosomes originating from the mother. Given the association of PHM with diandry, these results would appear to be at odds with the results of previous studies of placental morphology in triploids. The authors reviewed the placental pathology of all cases of triploidy examined at their institution over a 2-year period and established that PHM occurs in a minority of triploid conceptuses. These results support the findings of studies showing that digyny is the most common origin of triploidy.

The Mos/mitogen-activated protein kinase (MAPK) pathway regulates the size and degradation of the first polar body in maturing mouse oocytes

Mos is an upstream activator of mitogen-activated protein kinase (MAPK) and, in mouse oocytes, is responsible for metaphase II arrest. This activity has been likened to its function in Xenopus oocytes as a component of cytostatic factor. Thus, Mos-deficient female mice (MOS-/-) are less fertile and oocytes derived from these animals fail to arrest at metaphase II and undergo parthenogenetic activation [Colledge, W. H., Carlton, M. B. L., Udy, C. B. & Evans, M. J. (1994) Nature (London) 370, 65-68 and Hashimoto, N., Watanabe, N., Furuta. Y., Tamemoto, B., Sagata, N., Yokoyama, M., Okazaki, K., Nagayoshi, M., Takeda, N., Ikawa, Y. & Aizawa, S. (1994) Nature (London) 370, 68-71]. Here we show that maturing MOS-/- oocytes fail to activate MAPK throughout meiosis, while p34cdc2 kinase activity is normal until late in metaphase II when it decreases prematurely. Phenotypically, the first meiotic division of MOS-/- oocytes frequently resembles mitotic cleavage or produces an abnormally large polar body. In these oocytes, the spindle shape is altered and the spindle fails to translocate to the cortex, leading to the establishment of an altered cleavage plane. Moreover, the first polar body persists instead of degrading and sometimes undergoes an additional cleavage, thereby providing conditions for parthenogenesis. These studies identify meiotic spindle formation and programmed degradation of the first polar body as new and important roles for the Mos/MAPK pathway.

The incidence of bovine diploid oocytes matured in vitro

The present work describes a cytogenetic study of in vitro matured bovine oocytes to determine the proportion of unreduced oocytes carrying the diploid number of chromosomes. Studied oocytes were derived either from a pool of oocytes collected from several different donors, or from oocytes collected separately from individual donors. In vitro maturation was performed by culturing immature oocytes for 24 h in TCM199-medium supplemented with estrous cow serum and hormones at 39 degrees C in 5% CO2. Chromosomal complement of in vitro matured oocytes was studied by Giemsa-staining and produced analyzable results in approximately 60% of the cases. The results revealed that approximately 75% of oocytes had matured to the MII stage in both groups of oocytes studied. Of these MII oocytes, 11 and 12.4% (from the oocyte pool or from individual cows, respectively) contained the diploid set of chromosomes. The occurrence of diploid MII oocytes was not quite uniform among donors: 40.5% of all cows produced one, 18.9% produced two and 2.7% (one cow) produced three diploid MII oocytes. However, a positive relationship between the number of MII oocytes in general and diploid MII oocytes among individual donors was not found. The possible factors that may lead to the formation of diploid MII oocytes observed under IVM procedures are discussed. The results of this study showed a higher incidence of diploid oocytes in cattle than previously reported.

Confined placental mosaicism for trisomies 2, 3, 7, 8, 9, 16, and 22: their incidence, likely origins, and mechanisms for cell lineage compartmentalization

Analysis of confined placental mosaicism (CPM) for trisomies 2, 3, 7, 8, 9, 16, and 22, in diagnostic chorionic villus sampling procedures, demonstrates apparent incidences of CPM for individual trisomies of between 9 and 91 cases per 100,000 pregnancies, with trisomy 7 being the most common. More detailed analysis of the percentage of aneuploid cells present, and the distribution of abnormality between the cytotrophoblast and extra-embryonic mesoderm cell lineages, shows a highly specific pattern for each chromosome. Theoretical considerations, in conjunction with direct observations, indicate that the overriding influence on the patterns of cell distribution seen in CPM is the distribution of aneuploid cells laid down during blastogenesis. This in turn reflects closely the origin of mosaicism from either correction of a trisomic conception or post-fertilization somatic error. The pattern of aneuploid cells for each trisomy, as seen at the end of the first trimester and later in pregnancy, can therefore be used to predict the relative contribution of meiotic and mitotic errors to CPM, and hence the likely incidences of uniparental disomy from this source, upd(16)mat being the most common (1 in 10,000 continuing pregnancies). In addition, CPM for trisomies 2, 3, and 8 shows strong evidence of a non-random distribution of aneuploid cells between the different extra-embryonic cell lineages. Analysis of comparable data from spontaneous abortion material repeats this non-random pattern for trisomies 2 and 3, and suggests that a similar phenomenon may also be occurring for trisomy 22. A non-random distribution could be attributable to selection for or against, or intolerance of, particular trisomic cells in certain lineages, but is more probably a result of either cell lineage-specific non-disjunction or consistent uneven compartmentalization of aneuploid cells during blastocyst development.

Is genomic imprinting involved in the pathogenesis of pseudotriploid neuroblastoma?

Neuroblastoma is the most common solid tumor in children. It derives from the neural crest and originates from the sympathetic neuronal lineage [1-3]. At least two distinct biological-clinical entities can be distinguished [3-6]. One favorable subset occurs exclusively in infants and consists of early stages (I and II) as well as widespread disease (stage IV-S) at diagnosis. These tumors are commonly characterized by a hyperdiploid or pseudotriploid karyotype, but lack structural chromosome abnormalities. In particular, 1p abnormalities or N-mycgene amplification are not observed. Virtually all tumors identified with mass screening have belonged to these lower stages [4, 7, 8]. These patients show an excellent clinical outcome despite no or only minimal therapy. The other group of unfavorabled neuroblastomas is associated with older age and advanced stages (stages III and IV), and pseudodiploid karyotypes including lp deletions and N-myconcogene amplification [2, 9]. Their outcome remains poor despite aggressive multimodality therapy and bone marrow transplantation. It is interesting to note that favorable neuroblastomas rarely, if ever, evolve into unfavorable disease [3].

Asynchronous replication patterns of imprinted genes in triploid cells

Several unique features distinguish imprinted from nonimprinted genes, including the unusual replication behavior the unequal methylation and the differential expression of imprinted alleles [1]. The replication timing in S phase of the two homologous alleles of a normal, nonimprinted gene is highly synchronous [2, 3]. Housekeeping genes replicate early, constitutive heterochromatic regions replicate late and tissue-specific genes replicate earlier when they are expressed than when they are not [2-4]. In contrast, imprinted genes which, by definition, display allele-specific expression replicate asynchronously [2-5].

The relative order of replication of homologous alleles as well as that of different loci can be elegantly compared with fluorescence in situ hybridization (FISH) on interphase nuclei [2-5]. Unreplicated DNA segments give singlet hybridization signals in normal diploid cells, while replicated loci are characterized by doublets. The distribution of these two patterns can be used to determine the S phase replication time of any DNA sequence. Moreover, determination of the singlet/doublet ratio allows a good estimation of the degree of replication asynchrony of two homologous alleles [2-5].

Using cell lines with deletions, disomies or associated FISH-detectable centromeric satellite polymorphisms, Kitsberg et al. [4] found that the paternal allele was the early replicating one in all the imprinted genes which they had analyzed. Subsequently, however, Knoll et al. [5] detected genes in the imprinted Prader-Willi region on chromosome 15, which also displayed other patterns. Therefore, it seems necessary to specify the relative timing of maternally and paternally derived alleles for each individual asynchronously replicating gene. Unfortunately, this is so far only feasible with a very restricted number of sequences.

Maternal origin of extra haploid set of chromosomes in third trimester triploid fetuses

Twenty-six highly polymorphic markers were used to determine the origin of the extra haploid chromosome set in 6 triploid fetuses of type II phenotype. All had reached the third trimester of pregnancy. The extra set was maternal in origin in all cases, supporting previous research indicating longer in utero survival of maternally-derived triploid fetuses. These findings provide evidence for an instance of genomic imprinting in humans.

Parental origin of the extra haploid chromosome set in triploidies diagnosed prenatally

The parental origin of the additional chromosome complement in a total of 17 cases of triploidy was determined mainly using highly polymorphic microsatellites. Maternal origin of the triploidy was demonstrated in most cases. To the best of our knowledge, this is the first systematic evaluation of the parental origin of chromosome sets in fetuses who survived until a cytogenetic diagnosis was established. In contrast to previous investigations this study documented a predominance of maternal origin of the extra haploid set mainly due to longer survival time for digynic triploidies. The concept of 2 distinct fetal phenotypes in triploidy is clearly supported by this study.