Origin of triploidy in spontaneous abortuses

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.

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.

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.

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

Two distinct phenotypes of triploid fetuses have been previously described and a correlation with parental origin of the triploidy has been suggested. We have studied the parental origin of the extra haploid set of chromosomes in nine triploid fetuses using analysis of DNA polymorphisms at a variety of loci. Maternal origin of the triploidy (digyny) was demonstrated in six fetuses with type II phenotype, paternal origin (diandry) in two cases with type I phenotype, and nonpaternity in one case. The predominance of digynic triploids in our study contrasts with the results reported in previous studies in which, through analysis of cytogenetic polymorphisms, paternal origin was found to account for the majority of triploid conceptuses. This difference may be accounted for by a combination of factors--the different methods of parental assignment used and analysis of a different subset of triploid conceptuses. The correlation between the observed phenotypes and the parental origin of triploidy may represent another example of imprinting in human development.

Differentiation of binuclear spermatozoa in mice

In an electron microscopy study of abnormal spermatogenesis in mice, we have found that two discrete haploid nuclei may be located in a single spermatid cytoplasm after the second meiotic division. The spermatid continues to differentiate and forms a binucleate spermatozoon with both nuclei separately packaged within the sperm head. The Golgi apparatus of the double spermatid forms a single proacrosome that attaches to both nuclei. Apparently, one acrosomal structure differentiates to cover and compartmentalize the two haploid nuclei within the sperm head. Chromatin condensation appears normal. The head morphology and number of flagella vary in mature spermatozoa produced by this process. This work demonstrates one pathway by which polyploid spermatids continue to differentiate to spermatozoa after failure of cytoplasmic division or possibly cellular fusion.

Endocrine profile of follicles containing oocytes with subsequent polyploid fertilization

In an attempt to identify oocytes at risk for polypronuclear fertilization, follicular fluids were obtained retrospectively that contained oocytes that fertilized normally and abnormally. Whenever possible, each patient served as her own control during the same stimulation cycle. Twenty-six of 169 patients had oocytes that became polypronuclear, and of those 26, 21 had oocytes that fertilized and cleaved normally. Follicular fluids were analyzed for estradiol, progesterone, androstenedione, transferrin, and insulin. Insulin levels were noted to be significantly elevated (P less than 0.05) in the polypronuclear group when compropose that insulin, a known growth factor for granulosa cells cultured in vitro, when present in excessive concentrations may predispose to polypronuclear fertilization.

Triploid embryo after in vitro fertilization

A case of a triploid embryo (69,XXX) resulting from in vitro fertilization is reported. The pregnancy ended in spontaneous abortion 44 days after embryo transfer. The embryo showed anomalies considered typical of triploidy but molar changes were not noted. The origin of extra chromosomes was apparently maternal.

Triploidy, partial mole and dispermy. An investigation of 12 cases

Twelve triploid abortuses were investigated to determine the origin of the additional haploid set and were retrospectively examined for the development of partial hydatidiform mole. Eight out of ten suitable triploids were diagnosed as partial mole. Dispermy was indicated as the cause of triploidy in 6 informative cases of which 3 were also partial moles. However, one diandric triploid had no features of partial mole. The problem of maternal cell contamination in triploids and the difficulty of diagnosing partial moles on pathological grounds alone are discussed.

Low doses of X-rays decrease the risk of diploidy in mouse oocytes

Females from the NMRI/Han mouse strain ovulate a high number of diploid oocytes (about 12%) after gonadotrophin-stimulated ovulation. These oocytes can be fertilized and develop into triploid embryos subsequently. The exposure of such gonadotrophin-primed females to X-ray doses of 0.05, 0.10, 0.20 or 0.40 Gy during the preovulatory period (2 h after the HCG dose) significantly decreased the percentage of diploid oocytes. After the highest dose used, i.e. 0.80 Gy, however, the incidence was on the level from unirradiated females, again. We suggest that the observed negative hump-shaped dose response of diploidy is not caused by secondary modifications induced by irradiation, such as a selective killing of diploid oocytes before ovulation, or a (compensatory) super-ovulation of only normal oocytes, but rather is caused by a direct radiobiological interference of low doses in protecting from gonadotrophin-induced aneuploidy.

Further studies on effects of X-irradiation on prespermatid stages of the Northern vole Microtus oeconomus: low induction of sex-chromosomal nondisjunction and very high induction of diploid spermatids

Microtus males have been irradiated with X-ray doses of 25, 50, 100 and 200 rad and early spermatids were then analyzed for evidence of induction of sex-chromosomal nondisjunction and diploid spermatids at 1, 4, 6, 7, 9 and 12 days after treatment. In contrast to earlier findings, there was no induction of nondisjunction above control levels. A possible explanation for the differences in results of old and new experiments might be that genetic changes have taken place in the Microtus colony that was initiated with animals trapped in the wild, but which has now become highly inbred. In the present experiment, diploid spermatids were frequently induced. The dose--effect relationships at the different time intervals were linear, but the slopes were different, indicating stage-specific differences in sensitivity. The average doubling dose is of the order of 12 rad with a range of 5-30 rad for the individual time intervals. When diploid spermatozoa in man are also inducible by such low doses of X-rays, the consequence would be an increase of triploid abortions which would constitute an undesirable form of personal or family hardship.

Non-disjunction in trisomy 21: study of chromosomal heteromorphisms in 110 families

QM variants on chromosome 21 and silver staining of NOR regions were applied in the study of non-disjunction in 110 families from different parts of Denmark. In 76% of the families the study was informative. Paternal failures were observed in 11% on Funen as compared 23.5% on Zealand. In one family, crossing-over on the short arms of chromosome 21 in the mother and mitotic non-disjunction of chromosome 21 was observed. Maternal first meiotic error predominates in both high maternal and low maternal age. Also in paternal non-disjunction failures of first meiotic division predominate. Two maternally and one paternally originated cases of de novo translocations were observed.