Trisomy 1 in an eight cell human pre-embryo

Confined placental mosaicism and the association with pregnancy outcome and fetal growth: a review of the literature

BACKGROUND

Chromosomal mosaicism can be detected in different stages of early life: in cleavage stage embryos, in blastocysts and biopsied cells from blastocysts during preimplantation genetic testing for aneuploidies (PGT-A) and later during prenatal testing, as well as after birth in cord blood. Mosaicism at all different stages can be associated with adverse pregnancy outcomes. There is an onward discussion about whether blastocysts diagnosed as chromosomally mosaic by PGT-A should be considered safe for transfer. An accurate diagnosis of mosaicism remains technically challenging and the fate of abnormal cells within an embryo remains largely unknown. However, if aneuploid cells persist in the extraembryonic tissues, they can give rise to confined placental mosaicism (CPM). Non-invasive prenatal testing (NIPT) uses cell-free (cf) DNA released from the placenta in maternal blood, facilitating the detection of CPM. In literature, conflicting evidence is found about whether CPM is associated with fetal growth restriction (FGR) and/or other pregnancy outcomes. This makes counselling for patients by clinicians challenging and more knowledge is needed for clinical decision and policy making.

OBJECTIVE AND RATIONALE

The objective of this review is to evaluate the association between CPM and prenatal growth and adverse pregnancy outcomes. All relevant literature has been reviewed in order to achieve an overview on merged results exploring the relation between CPM and FGR and other adverse pregnancy outcomes.

SEARCH METHODS

The following Medical Subject Headings (MESH) terms and all their synonyms were used: placental, trophoblast, cytotrophoblast, mosaicism, trisomy, fetal growth, birth weight, small for gestational age and fetal development. A search in Embase, PubMed, Medline Ovid, Web of Science, Cochrane Central Register of Controlled Trials (CENTRAL) and Google Scholar databases was conducted. Relevant articles published until 16 July 2020 were critically analyzed and discussed.

OUTCOMES

There were 823 articles found and screened based on their title/abstract. From these, 213 articles were selected and full text versions were obtained for a second selection, after which 70 publications were included and 328 cases (fetuses) were analyzed. For CPM in eight different chromosomes (of the total 14 analyzed), there was sufficient evidence that birth weight was often below the 5th percentile of fetal growth standards. FGR was reported in 71.7% of CPM cases and preterm birth (<37 weeks of delivery) was reported in 31.0% of cases. A high rate of structural fetal anomalies, 24.2%, in cases with CPM was also identified. High levels of mosaicism in CVS and presence of uniparental disomy (UPD) were significantly associated with adverse pregnancy outcomes.

WIDER IMPLICATIONS

Based on the literature, the advice to clinicians is to monitor fetal growth intensively from first trimester onwards in case of CPM, especially when chromosome 2, 3, 7, 13, 15, 16 and 22 are involved. In addition to this, it is advised to examine the fetuses thoroughly for structural fetal anomalies and raise awareness of a higher chance of (possibly extreme) premature birth. Despite prematurity in nearly a fifth of cases, the long-term follow-up of CPM life borns seems to be positive. More understanding of the biological mechanisms behind CPM will help in prioritizing embryos for transfer after the detection of mosaicism in embryos through PGT-A.

1(st) trimester miscarriage: four decades of study

Miscarriage is a very common occurrence in humans. This paper sets out to present published data on research that has provided increased understanding of pregnancy failure. Clarification of definitions, exploring the range of failures from preclinical to later pregnancy losses, and the scientific tools employed to find information on the losses have been documented. What is now understood, which tools work best, and the associated limitations are all discussed. Early studies used cytogenetic methods and tissue culture to obtain results. Improvements in laboratory tools such as better tissue culture incubators, inverted microscopes, laminar flow hoods, improvements in culture media, all contributed to obtaining more results for patients. These studies demonstrated the significant contribution of unbalanced chromosomal karyotypes to pregnancy failure. Maternal age as a contributing factor in trisomy was clearly demonstrated. First trimester miscarriage exhibits very high cytogenetic abnormality; in contrast to very low rates in later losses. Combining data across all time periods of pregnancy will affect the significance of chromosomal error in the early pregnancy failures. Cytogenetic methods investigate whole genomes, and are considered to represent the standard against which new methods must be validated. New molecular genetic methods provide the opportunity to examine samples without the necessity of tissue culture. Techniques may be site-specific or whole genome. Fluorescent in situ hybridisation (FISH), comparative genomic hybridisation (CGH), array-based CGH, single nucleotide polymorphism (SNP) detection, quantitative polymerase chain reaction (qPCR), and quantitative fluorescent PCR (QF-PCR), have all been utilised. In comparison studies with classical/conventional cytogenetics, each newer method offers advantages and limitations. At the present time, a combined approach using conventional and molecular methods will elucidate the cause of miscarriage for almost all samples. In a clinical setting this would be optimum.

X inactivation in triploidy and trisomy: the search for autosomal transfactors that choose the active X

Only one X chromosome functions in diploid human cells irrespective of the sex of the individual and the number of X chromosomes. Yet, as we show, more than one X is active in the majority of human triploid cells. Therefore, we suggest that (i) the active X is chosen by repression of its XIST locus, (ii) the repressor is encoded by an autosome and is dosage sensitive, and (iii) the extra dose of this key repressor enables the expression of more than one X in triploid cells. Because autosomal trisomies might help locate the putative dosage sensitive trans-acting factor, we looked for two active X chromosomes in such cells. Previously, we reported that females trisomic for 18 different human autosomes had only one active X and a normal inactive X chromosome. Now we report the effect of triplication of the four autosomes not studied previously; data about these rare trisomies - full or partial - were used to identify autosomal regions relevant to the choice of active X. We find that triplication of the entire chromosomes 5 and 11 and parts of chromosomes 1 and 19 is associated with normal patterns of X inactivation, excluding these as candidate regions. However, females with inherited triplications of 1p21.3-q25.3, 1p31 and 19p13.2-q13.33 were not ascertained. Thus, if a single key dose-sensitive gene induces XIST repression, it could reside in one of these locations. Alternatively, more than one dosage-sensitive autosomal locus is required to form the repressor complex.

Effect of paternal age on the frequency of cytogenetic abnormalities in human spermatozoa

Many surveys have been performed to find etiological relationships between pregnancy outcome and specific risk factors, such as exposure to chemicals and radiation or parental age. Advanced maternal age is a strong risk factor for trisomic pregnancies, albeit there are considerable variations among the different chromosomes. The definite incidence of the various structural and numerical chromosome aberrations in spontaneous abortions and liveborns is well known, as well as the rate of maternally and paternally derived rearrangements. Nevertheless studies have failed to assert an age-dependent risk for men fathering chromosomally abnormal children. New techniques using fluorescence in situ hybridization render it possible to analyze spermatozoa directly for numerical and, to some extent, for structural aberrations. This article compiles the findings of studies on human spermatozoa over the last few years.

Aneuploidy involving chromosome 1 in failed-fertilized human oocytes is unrelated to maternal age

PURPOSE

To study whether maternal meiotic errors in failed-fertilized oocytes involving chromosome 1 occur at frequencies similar to those involving other autosomes, and whether their frequency is affected by maternal age.

METHODS

Using fluorescence in situ hybridization (FISH), frequencies of aneusomy and chromatid pre-division involving chromosomes 1, 16, 18, and 21 were determined for 273 failed-fertilized oocytes.

RESULTS

The aneuploidy rate for chromosome 1 was 15.8%, and was neither age-dependent nor significantly different from that for chromosomes 16, 18 or 21. Only chromosome 16 exhibited an age-dependent increase in aneusomy rates. The frequency of chromatid pre-division was lower for chromosome 1 than for chromosome 18 (11.9% vs. 25.4%; p = 0.01), but not different from that for chromosomes 16 or 21.

CONCLUSION

Aneuploidy involving chromosome 1 in failed-fertilized oocytes is unrelated to maternal age and occurs at a frequency similar to that for chromosomes 16, 18, and 21.

Chromosomal anomalies in first-trimester miscarriages

BACKGROUND

It is well known that a large proportion of first-trimester spontaneous abortions is caused by chromosomal disorders. The present study represents a unique material and the success rate of the karyotyping was high.

METHODS

Chromosomal analysis from chorionic villus sampling of 259 of 304 consecutive first-trimester miscarriages in the Uppsala County, Sweden is presented.

RESULTS AND CONCLUSIONS

An abnormal karyotype was found in 61% of the cases. Autosomal trisomies were most frequently detected (in 37% of the karyotyped samples), followed by polyploidies (9%) and monosomy X (6%). Cases with an extra sex chromosome constituted approximately 5% of the karyotyped abortions, with a remarkable high frequency of 47,XXY (3.4%), that is approximately 40 times greater the prevalence of Klinefelter syndrome among live birth. Similar to autosomal chromosome abnormalities, present finding indicates that the majority of sex chromosome abnormalities do not survive to term. Autosomal trisomies and an extra X-chromosome in males (47,XXY) were associated with an advanced maternal age, whereas monosomy X as well as polyploidy changes seems to be inversely related to the age of the mother. The single most common aberration was trisomy 16, which was found in 14% of the chromosomally abnormal abortions.

Trisomy 1 in a case of a missed abortion

Most chromosomal trisomies lead to miscarriages. In all trisomies, trisomy 1 is the most rare case. We herein present a patient who demonstrated a gestational sac and a yolk sac on transvaginal ultrasound. However, at 53 days of gestation, the pregnancy was lost with a diagnosis of a blighted ovum. A D&C was recommended and performed. A cytogenetic analysis from chorionic villi demonstrated a 47,XX,+1 chromosome complement in all 100 cells. Regarding full trisomy 1, there has only been one case report of a preembryo and two case reports in a clinically recognized pregnancy to date.

Differences in chromosome susceptibility to aneuploidy and survival to first trimester

The purpose of this study was to find specific rates of aneuploidy in cleavage-stage embryos compared with first trimester data and to evaluate post-zygotic selection against aneuploidy. A total of 2058 embryos were analysed by flurorescence in-situ hybridization (FISH), and specific aneuploidy rates were obtained for 14 chromosomes. Data from morphologically abnormal embryos could be pooled with data from preimplantation genetic diagnosis (PGD) cycles because it was observed that they had similar rates of aneuploidy; thus, for the purpose of studying aneuploidy they could be, and were, pooled. Specific chromosome aneuploidy rates were not related to morphology or development of the embryos. The average maternal age of patients with aneuploid embryos was significantly higher than the overall analysed population. Monosomy appeared more commonly than trisomy. The chromosomes most frequently involved in aneuploidy were (in order) 22, 16, 21 and 15. When compared with first trimester pregnancy data, aneuploidies detected at cleavage stage seem to die in excess of 90% before reaching first trimester, with the exception of chromosome 16 and gonosomes (76% and 14% respectively). Differences in chromosome-specific aneuploidy rates at first trimester conceptions are probably produced by different chromosome-specific aneuploidy rates at cleavage stage and different survival rates to first trimester.

Prenatal detection of mosaic trisomy 1q due to an unbalanced translocation in one fetus of a twin pregnancy following in vitro fertilization: a postzygotic error

Complete or mosaic trisomy for all of chromosome 1q has been seen rarely in a recognized pregnancy. A patient presented with twins following in vitro fertilization (IVF). Ultrasound showed twin A to have a diaphragmatic hernia, thick nuchal fold, and subtle intracranial abnormalities. Twin B appeared normal and a thick dividing membrane was seen. Amniocentesis of twin A showed a male karyotype with mosaic trisomy 1q in 57% of cells resulting from a translocation between chromosomes Yq12 and 1q12. Parental karyotypes were normal. The twins were delivered at 33 weeks. Twin A died at 1 hr of life. Autopsy confirmed the left diaphragmatic hernia and hypoplastic lungs. Autopsy also revealed a partial cleft palate, syndactyly of the second and third toes bilaterally, external deviation of the left 5th toe, and contractures of the index fingers bilaterally. A recent report documented formation of a chimera resulting from embryo amalgamation after IVF. Given the rarity of the cytogenetic findings in our case, we sought to determine if the mosaicism was a result of chimera formation related to the IVF. Thirteen polymorphic loci throughout the genome, in addition to four on 1q and four on 1p, were amplified by PCR. Only two alleles were observed at each of these loci in twin A, one paternal and the other maternal. We present further clinical findings of this case with a rare cytogenetic abnormality that appears to have originated from a postzygotic mitotic error and not embryo amalgamation.

Different probe combinations for assessment of postzygotic chromosomal imbalances in human embryos

PURPOSE

We compared three different probe combinations for detection of postzygotic mosaic imbalances in human preimplantation embryos.

METHODS

Two hundred and two spare cleavage stage embryos were hybridized with fluorescently labelled DNA probe mixtures specific to chromosomes X, Y, 18 (N = 67), chromosomes 2, 7, 18 (N = 71), or chromosomes 13, 16, 18, 21, 22 (N = 64).

RESULTS

An overall higher incidence of abnormalities was detected using probe mixture for five (69%) or three (72%) autosomes compared to one autosome and chromosomes X and Y (54%). The rate of aneuploidy detected increased with the number of autosomes hybridized from 4% (X, Y, 18) to 11% (2, 7, 18) to 19% (13, 16, 18, 21, 22). Postzygotic mosaicism comprised the most frequent abnormality detected by all probe combinations, and the percentage detected by each was similar, 48% (X, Y, 18), 56% (2, 7,18), and 50% (13,16,18, 21, 22).

CONCLUSIONS

A probe combination of five autosomes, particularly those of clinical relevance, may be more beneficial for screening embryos from patients at risk of maternal-age-related aneuploidy. However, all three probe combinations are as efficient at identifying postzygotic mosaicism, and may be used for identifying embryos with less potential of developing to term.

De novo interstitial direct duplication 1(q23.1q31.1) in a fetus with Pierre Robin sequence and camptodactyly

Interstitial duplications of chromosomal region 1q are rarely seen. We report the first prenatal diagnosis of pure partial trisomy 1q. The fetus was karyotyped for polyhydramnios, micrognathia, and flexion of fingers of both hands. Conventional and molecular cytogenetics showed a de novo direct duplication of the chromosomal region 1q23.1q31.1 leading to a partial trisomy 1q. At autopsy, the fetus showed Pierre Robin sequence (PRS) and camptodactyly. The main histological finding was a decreased number of motoneurons with apoptotic features in the anterior horn of the spinal cord. A literature review and our observations suggest that genetic material mapping to chromosome 1q25 could be responsible for PRS with distal arthrogryposis when this is in triple dose.

Chromosomal anomalies in human gametes and pre-implantation embryos, and their potential effect on reproduction

This paper reviews the latest data on chromosomal abnormalities in human gametes and embryos. A close relationship between such anomalies and reproduction failure in humans has been postulated, thereby underscoring the importance of ongoing studies into the mechanisms leading to anomalies. Until recently, knowledge of chromosomal anomalies in human gametes and embryos has been limited. Newly developed strategies (in vitro fertilization combined with micromanipulation techniques followed by multicolour fluorescence in situ hybridization, and PCR analyses) allow precise investigation of this problem. This review of the available information on the etiology of chromosomal anomalies indicates that some of the genetic anomalies in human gametes and early embryos result in reproductive failure.

Positive outcome after preimplantation diagnosis of aneuploidy in human embryos

usromosomal abnormalities are responsible for a great deal of embryo wastage, which is reflected, at least partially, in decreased implantation and increased miscarriage in older women. To address this problem the transfer of only chromosomally normal embryos previously selected by preimplantation genetic diagnosis (PGD) has been proposed. We designed a multi-centre in-vitro fertilization (IVF) study to compare controls and a test group that underwent embryo biopsy and PGD for aneuploidy. Patients were matched retrospectively, but blindly, for average maternal age, number of previous IVF cycles, duration of stimulation, oestradiol concentrations on day +1, and average mature follicles. All these parameters were similar in test and control groups. Only embryos classified as normal for those chromosomes were transferred after PGD. The results showed that the rates of fetal heart beat (FHB)/embryo transferred between the control and test groups were similar. However, spontaneous abortions, measured as FHB aborted/FHB detected, decreased after PGD (P < 0.05), and ongoing pregnancies and delivered babies increased (P < 0.05) in the PGD group of patients. Two conclusions were obtained: (i) PGD of aneuploidy reduced embryo loss after implantation; (ii) implantation rates were not significantly improved, but the proportion of ongoing and delivered babies was increased.

Preimplantation genetic diagnosis of aneuploidy: were we looking at the wrong chromosomes?

PURPOSE

Our purpose was to study aneuploidy frequencies of chromosomes 1, 4, 6, 7, 14, 15, 17, 18, and 22 in cleavage-stage embryos. These frequencies were compared to spontaneous abortion data to determine differences in survival rate of their aneuploidies.

METHODS

One hundred ninety-four embryos were analyzed with multicolor fluorescence in situ hybridization. Embryos were divided into three maternal age groups: 20 to 34.9 years, (2) 35 to 39.9 years, and (3) 40 years and older. Embryos were also divided into two developmental and morphological groups; arrested and nonarrested embryos.

RESULTS

The rate of aneuploidy was 14.51%, 14.10%, and 31.48% for age groups 1, 2, and 3, respectively (P < 0.005). The chromosomes most frequently involved in aneuploidy events were 22, 15, 1, and 17.

CONCLUSIONS

The chromosomes most involved in spontaneous abortions are not necessarily the ones causing a decrease in implantation rates with maternal age. Other aneuploidies, such as for chromosomes 1 and 17, may seldom implant or die shortly after implantation.

Chromosomally abnormal early ongoing pregnancies: correlation of ultrasound and placental histological findings

The pathophysiology of placental microscopic changes in chromosomally abnormal pregnancies remains poorly understood. We have reviewed the relationship between ultrasound findings and villous histological features in a group of 25 ongoing pregnancies presenting with fetal aneuploidy at 11 to 15 weeks of gestation. The chromosomal abnormalities were diagnosed by chorion villous sampling, and the data were compared with those of a group of 25 chromosomally normal pregnancies undergoing surgical termination and matched for gestational age. The aneuploid group included 10 pregnancies with trisomy 21, nine with trisomy 18, three with triploidy, two with monosomy X, and one with trisomy 13. The overall degree of agreement between the two investigators for the histological diagnosis was good (kappa, 0.64), and the sensitivity of histology ranged between 72.0% and 80.0%. Fetal and placental edema was observed on scan in 10 and 7 cases, respectively, of the aneuploid group and was systematically associated with trophoblastic hypoplasia, stromal edema, or cavitation, reduced vascularization, and ramification of the main villous trunks. Fetoplacental hydrops was not observed in the euploid group. These findings indicate that histological changes observed in the placenta of fetuses from ongoing pregnancies presenting with aneuploidy can be linked with early fetal hydrops. The villous features in these cases are probably secondary to a reduction in the villous circulation due to a cardiovascular defect and leading to generalized stromal edema. The reduced villous branching and trophoblastic hypoplasia could be secondary to the enlargement of all villous types or to a basic defect in placental development.

Multiple congenital malformations in an infant prenatally diagnosed with mosaicism for dup(lq) and del(Xq)

After ultrasound diagnosis of a fetus with severe hydrocephalus and Dandy-Walker malformation, amniocentesis revealed chromosomal mosaicism for dup(lq) and del(Xq). The neonate had dysmorphic facial features, vertebral abnormalities, and pulmonary hypoplasia, and expired shortly after birth. This report confirms the poor prognosis reported for partial trisomies involving the long arm of chromosome number 1.

Aneuploidy in human sperm: the use of multicolor FISH to test various theories of nondisjunction

While it is known that all chromosomes are susceptible to meiotic nondisjunction, it is not clear whether all chromosomes display the same frequency of nondisjunction. By use of multicolor FISH and chromosome-specific probes, the frequency of disomy in human sperm was determined for chromosomes 1, 2, 4, 9, 12, 15, 16, 18, 20, and 21, and the sex chromosomes. A minimum of 10,000 sperm nuclei were scored from each of five healthy, chromosomally normal donors for every chromosome studied, giving a total of 418,931 sperm nuclei. The mean frequencies of disomy obtained were 0.09% for chromosome 1; 0.08% for chromosome 2; 0.11% for chromosome 4; 0.14% for chromosome 9; 0.16% for chromosome 12; 0.11% for chromosomes 15, 16, and 18; 0.12% for chromosome 20; 0.29% for chromosome 21; and 0.43% for the sex chromosomes. Data for chromosomes 1, 12, 15, and 18, and the sex chromosomes have been published elsewhere. When the mean frequencies of disomy were compared, the sex chromosomes and chromosome 21 had significantly higher frequencies of disomy than that of any other autosome studied. These results corroborate the pooled data obtained from human sperm karyotypes and suggest that the sex chromosome bivalent and the chromosome 21 bivalent are more susceptible to nondisjunction during spermatogenesis. From these findings, theories proposed to explain the variable incidence of nondisjunction can be supported or discarded as improbable.

Chromosomal differences in susceptibility to meiotic aneuploidy

A basic question concerning the origins of germ cell aneuploidy is whether the same mechanisms operate for all chromosomes, or whether there are chromosome-specific factors influencing the susceptibility to nondisjunction. Although selective loss of some trisomies in early gestation may contribute to the observed differences in trisomy frequency, data from spontaneous abortions, early embryos and gametes strongly suggest that there are real differences in the frequency with which different trisomies arise. In particular the preponderance of trisomy 16 and acrocentric trisomy appears to be present at conception. Maternal and paternal age relationships also differ among trisomies, as do the extent of maternal and paternal contributions, and the relative frequency of meiosis I and meiosis II errors. Recombination patterns associated with nondisjunction also show chromosomal differences. Chromosomal differences in length, centromere position, pericentromeric and other repetitive sequences, recombination patterns and chromatin characteristics might all be related to a differential susceptibility to aneuploidy, but no current explanation accounts for the excess of maternally derived trisomy 16. The existence of chromosome-specific factors makes extrapolation from observations on one chromosome to all aneuploidy unwise, both for investigations into the causes of aneuploidy, and for surveillance of aneuploidy frequency.

The relationship between paternal age, sex ratios, and aneuploidy frequencies in human sperm, as assessed by multicolor FISH

We studied the frequencies of X- and Y-chromosome-bearing sperm, diploidy and disomy for chromosomes 1, 12, X, and Y in sperm from 10 normal men aged 21-52 years, to determine whether there was any relationship between donor age and any of these variables. Multicolor FISH was used to control for lack of probe hybridization and to distinguish diploid sperm from disomic sperm. A minimum of 10,000 sperm per donor was evaluated for each chromosome, for a total of 225,846 sperm studied. Sperm were considered disomic if two fluorescent signals were separated by a minimal distance of one signal domain. The mean frequencies of X- and Y-bearing sperm were 50.1% and 49.0%, respectively; not significantly different from 50%. There was no correlation between paternal age and "sex ratio" in sperm. Similarly, there was no association between the frequency of diploid sperm (mean, .16%; range, .06-.42%) and donor age. For disomy frequencies, there was no relationship between donor age and disomy 12 (mean, .16%; range, .10%-.25%), XX (mean, .07%; range, .03%-.17%), and XY sperm (mean, .16%; range, .08%-.24%). There was a significant increase in the frequency of YY sperm (P = .04; mean, .18%; range, .10%-.43%) and disomy 1 sperm (P = .01; mean, .11%; range, .05%-.18%) with donor age. In summary, our results do not support a correlation between paternal age and sex ratio or diploidy.

Mosaicism of autosomes and sex chromosomes in morphologically normal, monospermic preimplantation human embryos

We have previously detected chromosome abnormalities in human embryos whilst identifying the sex for preimplantation diagnosis of X-linked disease. In this study we assess the incidence of these abnormalities, both for sex chromosomes and autosomes 1 and 17, using dual fluorescent in situ hybridization (FISH). Sixty-nine normally fertilized embryos of good morphology at the 6-10 cell stage (day 3 post-insemination) were examined. The embryos were spread whole using HCl and Tween 20 to dissolve the cytoplasm. Thirty-four embryos were analyzed for the sex chromosomes and 35 for autosomes 1 and 17. All probes were directly labelled with fluorochromes allowing analysis in 2 h. Control lymphocytes demonstrated that the probes were of high specificity. For the sex chromosomes, five embryos were mosaic (15 per cent) with the remaining 29 being uniformly XX or XY. In no case was an XX nucleus found in an otherwise XY embryo, indicating that even though mosaicism for the sex chromosomes is present, such abnormalities would not lead to a misdiagnosis of sex. For the autosomes, 16 embryos were abnormal (46 per cent); one embryo was triploid, one was monosomic for chromosome 1, and ten others were diploid mosaics (three diploid/aneuploid, three diploid/polyploid, and four diploid/haploid). A further four embryos had variable chromosome numbers in the majority of nuclei which appeared to be the result of uncontrolled mitotic division. The presence of haploidy or double monosomy, which occurred in 15 per cent of nuclei, has important implications for the diagnosis of trisomies and dominant disorders.

Numerical chromosome abnormalities in spermatozoa of fertile and infertile men detected by fluorescence in situ hybridization

Fluorescence in situ hybridization (FISH) with single-color chromosome-specific probes was used to study the rates of disomy for chromosome 1, 16, X, and Y in sperm of fertile and infertile subjects. Diploidy rates were studied using a two-color cocktail of probes for chromosomes 17 and 18 in the same sperm samples. Two-color methodology was not available at the outset of the study. A total of 450,580 spermatozoa were studied from 21 subjects (9 fertile, 12 infertile). Significant differences were observed in the disomy rates between chromosomes with the highest frequency observed for chromosome 16 (0.17%) and the lowest for the Y chromosome (0.10%). No differences were observed between fertile and infertile subjects for either diploidy or disomy. Total disomy rates for chromosomes 1, 16, X and Y ranged from 0.34% to 0.84% among infertile subjects, and 0.32% to 0.61% among fertile subjects. Our data suggest that generalized aneuploidy in sperm is not a major contributor to unexplained infertility.

Cytogenetic analysis of the oocyte and embryo after removal of the zona pellucida following failed fertilization

Cytogenetic analysis of the oocyte and embryo after removal of the zona pellucida provides a simple screening method for examining the oocyte and embryo and considering the morphological abnormalities of the zona and adjacent formations, cytoplasm and nucleus. Seventy-one unfertilized oocytes and 27 embryos with poor morphology or cleavage arrest were studied after fixation, staining and mechanical removal of the zona. Fixation was done with a glutaraldehyde solution (1%). The oocytes and embryos were then stained, causing weakening of the zona. A slight pressure on the cover slide led to rupture of the zona and the exposure of the oolema. The oocytes and embryos were analyzed for sperm attachment to and penetration through the zona, appearance of the polar bodies, differentiation of blastomeres from cytoplasmic fragments, nuclear status--pyknotic non-analyzable form, chromosomes or different degenerative appearances of DNA. Peeling of the zona is an easy and reliable screening technique needing only an ordinary light microscope. It provides the advantage of observing the whole structure of the oocyte-embryo, not just the chromosomes as in classical cytogenetic methods.

Detection of aneuploid human sperm by fluorescence in situ hybridization: evidence for a donor difference in frequency of sperm disomic for chromosomes 1 and Y

Fluorescence in situ hybridization with repetitive-sequence DNA probes was used to detect human sperm disomic for chromosomes 1 and Y in three healthy men. Data on these same men had been obtained previously, using the human-sperm/hamster-egg cytogenetic technique, providing a cytogenetic reference for validating sperm hybridization measurements. Air-dried smears were prepared from semen samples and treated with DTT and lithium diiodosalicylate to expand sperm chromatin. Hybridization with fluorescently tagged DNA probes for chromosomes 1 (pUC177) or Y (pY3.4) yielded average frequencies of sperm with two fluorescent domains of 14.2 +/- 2.4/10,000 and 5.6 +/- 1.6/10,000 sperm, respectively. These frequencies did not differ statistically from frequencies of hyperploidy observed for these chromosomes with the hamster technique. In addition, frequencies of disomic sperm from one donor were elevated approximately 2.5-fold above those of other donors, for both chromosomes 1 (P = .045) and Y (P = .01), consistent with a trend found with the hamster technique. We conclude that fluorescence in situ hybridization to sperm chromosomes provides a valid and promising measure of the frequency of disomic human sperm.

Prospective study of short and ultrashort regimens of gonadotropin-releasing hormone agonist in an in vitro fertilization program

OBJECTIVE

To assess the usefulness of the ultrashort regimen of gonadotropin-releasing hormone agonist (GnRH-a) in ovulation induction in an in vitro fertilization (IVF) program.

DESIGN

A prospective randomized trial comparing short and ultrashort regimens of GnRH-a.

SETTING

Aberdeen Assisted Reproduction Unit.

PATIENTS

Forty-eight patients having IVF for the first time were randomized between the two protocols.

MAIN OUTCOME MEASURES

Response to ovarian stimulation and occurrence of spontaneous luteinizing hormone (LH) surges.

RESULTS

In ovulation induction, fertilization, and pregnancy rates the ultrashort regimen produces results that were no different to the short regimen but it did not always prevent an LH surge.

CONCLUSION

The ultrashort regimen can be a useful alternative for ovarian stimulation of patients undergoing IVF.

Prospective study of short and long regimens of gonadotropin-releasing hormone agonist in in vitro fertilization program

OBJECTIVE

To assess the usefulness of a short regimen in ovulation induction in an in vitro fertilization (IVF) program.

DESIGN

A prospective randomized trial was set up to compare long and short regimens of gonadotropin-releasing hormone agonist administration for ovulation induction in IVF.

SETTING

Aberdeen Assisted Reproduction Unit.

PATIENTS

Eighty-seven patients undergoing IVF were randomized between the two protocols. Stimulation regimen was the only variable being tested.

MAIN OUTCOME MEASURES

Stimulation response and occurrence of luteinizing hormone (LH) surges.

RESULTS

There was no difference in the stimulation requirements, response to stimulation, number of follicles aspirated, or the number of oocytes obtained. The fertilization rates, number of embryos transferred, and pregnancy rates were also similar in both groups. Like the long regimen, it prevents the occurrence of a premature LH surge.

CONCLUSION

The short regimen is a useful and cheaper alternative in ovarian stimulation of patients undergoing IVF.

Cytogenetics of human oocytes, zygotes, and embryos after in vitro fertilization

Chromosome errors, inherited or arising de novo during gametogenesis and transmitted at fertilization to the conceptus, may be a major cause of embryonic mortality. The in vitro fertilization and embryo transfer (IVF/ET) procedure provides extra material--oocytes, zygotes, and embryos--to investigate the contribution of chromosomal abnormality to implantation failure. This paper reviews the results of cytogenetic studies on such material. Estimates from a total of 1120 oocytes from 11 studies give an overall proportion of chromosomal abnormality of 35%. Single and multiple nullisomies and disomies are found, involving nonrandom chromosome gain or loss. Hypohaploid complements are more frequent than hyperhaploid complements. The higher rate of chromosome loss of hypohaploid karyotypes was found to be largely artifactual. The estimated overall frequency of aneuploidy is 13%. In embryos the level of chromosomal abnormality is 23%-40%. Errors of fertilization are responsible for a substantial number of triploid embryos, many of which develop into mosaics. Factors extrinsic to the conceptus, such as infertility, advanced maternal age, and ovarian hyperstimulation, may increase the level of chromosomal abnormality. More refined methods for accurately recognizing and selecting chromosomally normal embryos for transfer are needed to improve the success rate of this reproductive technology.

Non-isotopic detection of chromosome 1 in human meiosis and demonstration of disomic sperm nuclei

Nonradioactive in situ hybridization with the biotin-labeled chromosome 1-specific probe pUC1.77 was performed on human mitotic and meiotic chromosomes, and on sperm nuclei. The streptavidine-horseradish-peroxidase and diaminobenzidine detection system demonstrated heteromorphisms in the 1q12 heterochromatic region, not only in mitotic cells but also in mature sperm heads. The localization of chromosome 1 could be traced through all meiotic stages and in the sperm nuclei. The frequency of chromosome 1 disomy in human sperm, as indicated by two distinct hybridization signals, was calculated to be 0.41%.

Distribution of aneuploidy in human gametes: comparison between human sperm and oocytes

The frequency and distribution of aneuploidy was compared in 11,615 karyotyped human sperm and 772 karyotyped human oocytes to determine if all chromosomes are equally likely to be involved in aneuploid events or if some chromosomes are particularly susceptible to nondisjunction. The frequency of hypohaploidy and hyperhaploidy was compared among different chromosome groups and individual chromosomes for human sperm and oocytes. In general, hypohaploid chromosome complements were more frequent than hyperhaploid complements, in sperm and oocytes. The distribution of chromosome loss in the hypohaploid complements indicated that significantly fewer of the large chromosomes and significantly more of the small chromosomes were lost, suggesting that technical loss predominantly affects small chromosomes. A conservative estimate of aneuploidy (2 X hyperhaploidy) was approximately 3-4% in the human sperm and 18-19% in human oocytes. All chromosome groups were represented among hyperhaploid human sperm and oocytes. For human sperm, the observed frequency of hyperhaploidy equaled the expected frequency based on the assumption that the frequency of nondisjunction is equal for all chromosome groups, with two exceptions: group G and the sex chromosomes. Among individual chromosomes in human sperm, chromosomes 1 and 21 and the sex chromosomes had a significant excess of hyperhaploidy. For human oocytes, there were fewer hyperhaploid oocytes than expected for chromosome groups C and F and more than expected for chromosome groups D and G. Among individual chromosomes there was a significant excess for chromosome 21. These results indicate that all chromosomes are susceptible to nondisjunction but that chromosome 21 is particularly prone to aneuploidy in both human sperm and oocytes. They also demonstrate that sex chromosome aneuploidy is common in human sperm but not in human oocytes.

Nonisotopic in situ hybridization as a method for nondisjunction studies in human spermatozoa

Human spermatozoa were studied with a nonradioactive in situ hybridization method. Using a chemically modified DNA probe and immunocytochemical reactions for visualization, it was possible to obtain hybridization signals in 31 of 32 semen samples. Positive hybridization reactions, depending on cell accessibility, varied from 40% to over 90% for the different samples. Using a chromosome 1-specific DNA probe, disomy for this chromosome was found in 0.67% of all accessible sperm cells.

Incidence and timing of pregnancy losses: relevance to evaluating safety of early prenatal diagnosis

Knowing the frequency and timing of pregnancy loss during normal gestation is integral to evaluating the safety of prenatal diagnostic techniques. That preclinical loss rates are high in humans has long been suspected, but in the past decade new data concerning these losses have become available. Cohort studies indicate that many women who show positive beta-HCG assays never show clinical evidence of pregnancy. Cytogenetic abnormalities have also recently been documented in 20% of ostensibly normal in vitro fertilization embryos. All the above are consistent with the sentinel studies of Hertig and Rock, who showed high frequencies of morphological abnormalities in preimplantation embryos. The frequency of fetal losses after clinical recognition of pregnancy is 12-15%; however, more sensitive (ultrasonographic) methods of detecting fetal demise now indicate that most clinically recognized pregnancies occur prior to 8-9 weeks, being retained in utero 2-3 weeks prior to expulsion. Loss rates are influenced by maternal age, smoking, alcohol, and other confounding variables that if not taken into account could yield spurious results concerning safety of prenatal diagnostic techniques. After 8 weeks gestation the likelihood of losing a viable pregnancy is only 3% and after 16 weeks only 1%.

The effect of the antiprogestin mifepristone (RU 486) on maturation and in-vitro fertilization of human oocytes

The effect of RU 486 (mifepristone), a potent antiprogestin, on the in-vitro fertilization of human oocytes was investigated. In 40 normal volunteer women requesting laparoscopic sterilization, follicle aspiration for oocyte recovery was attempted 34 h after the injection of 5000 i.u. human chorionic gonadotrophin (hCG). Twenty women were allocated to receive 100 mg RU 486 orally 1 h before the hCG injection, the remaining 20 women acted as controls. There was no significant difference in the cleavage rate of the oocytes after fertilization in vitro between the two groups (56% and 66% respectively). Also, the morphological characteristics of the cleaving oocytes and the concentrations of oestradiol, progesterone and androstenedione in the follicular fluid of the leading follicle did not differ significantly between the two groups. Since RU 486 was detected in substantial amounts in the follicular fluid specimens, these results suggest that progesterone is not critical for the final stages of human oocyte maturation.

Sperm chromosome complements in a 47,XYY man

Human sperm chromosomes from a 47,XYY male were examined using the direct method of sperm chromosome analysis with two modifications in the semen processing. A total of 75 sperm complements was karyotyped and all of these contained one sex chromosome. The percentages of X- and Y-bearing sperm were 53% and 47%, respectively. There were 10 sperm with autosomal chromosomal abnormalities. The frequencies of numerical (4.0%), structural (10.6%), and total (13.3%) abnormalities were not significantly different from the frequencies observed in normal donors in our laboratory. Our results do not support the suggestion that XYY males have an increased risk of aneuploid progeny as a result of secondary non-disjunction or interchromosomal effects. They do support the hypothesis that one Y chromosome is eliminated in the germ cells of XYY males. However since our study provides the first information on sperm chromosomes in an XYY male, further studies on other XYY men are required.

The Farber lecture. Prenatal and perinatal death: the future of developmental pathology

It seems evident that most of "humanity" dies before, not after birth and that perhaps only one-third survive from earliest beginnings until birth or the end of the first year of life. As many as 50% of all human ova may have a chromosome abnormality with over 99% mortality, making this type of genetic defect not just the commonest cause of death prenatally and the cause of a substantial proportion of the malformations of abortuses and fetuses, but the commonest cause of death in humans altogether. This study, along with numerous studies before it, is the most convincing justification for doing autopsies on pre- and perinatally dead embryos and fetuses. With appropriate supervisory collaboration from a university pediatric pathology unit, such studies can be done efficiently at secondary-care centers, including some in rather remote locations. Thus, there exists no excuse anymore for not doing such studies which, in a high proportion of cases, will give the parents and attending physicians an explanation of the events and observed abnormalities with a chance in all cases at correct diagnostic and genetic counseling, appropriate monitoring of the next pregnancy, and an improved possibility of population monitoring for teratogens and substantial increases in the mutation rate. These immediate benefits to patients and the quality of medical care are the major, but not the only, justification for doing fetal pathology. Literally thousands of new discoveries still await the investigator with a prepared mind and will afford many research opportunities to those with an interest in normal and abnormal human development. And if it can be resolved in present-day pathology training programs how to attract greater numbers of interested residents and fellows into the field and to motivate them to take the additional training to become expert in developmental and genetic analysis, then "developmental" pathology will be facing a very bright future indeed.