Retrospective study of the parental origin of the extra chromosome in trisomy 18 (Edwards syndrome)

Germline cell de novo mutations and potential effects of inflammation on germline cell genome stability

Uncontrolled pathogenic genome mutations in germline cells might impair adult fertility, lead to birth defects or even affect the adaptability of a species. Understanding the sources of DNA damage, as well as the features of damage response in germline cells are the overarching tasks to reduce the mutations in germline cells. With the accumulation of human genome data and genetic reports, genome variants formed in germline cells are being extensively explored. However, the sources of DNA damage, the damage repair mechanisms, and the effects of DNA damage or mutations on the development of germline cells are still unclear. Besides exogenous triggers of DNA damage such as irradiation and genotoxic chemicals, endogenous exposure to inflammation may also contribute to the genome instability of germline cells. In this review, we summarized the features of de novo mutations and the specific DNA damage responses in germline cells and explored the possible roles of inflammation on the genome stability of germline cells.

Single-Cell Transcriptomics of Cultured Amniotic Fluid Cells Reveals Complex Gene Expression Alterations in Human Fetuses With Trisomy 18

Trisomy 18, commonly known as Edwards syndrome, is the second most common autosomal trisomy among live born neonates. Multiple tissues including cardiac, abdominal, and nervous systems are affected by an extra chromosome 18. To delineate the complexity of anomalies of trisomy 18, we analyzed cultured amniotic fluid cells from two euploid and three trisomy 18 samples using single-cell transcriptomics. We identified 6 cell groups, which function in development of major tissues such as kidney, vasculature and smooth muscle, and display significant alterations in gene expression as detected by single-cell RNA-sequencing. Moreover, we demonstrated significant gene expression changes in previously proposed trisomy 18 critical regions, and identified three new regions such as 18p11.32, 18q11 and 18q21.32, which are likely associated with trisomy 18 phenotypes. Our results indicate complexity of trisomy 18 at the gene expression level and reveal genetic reasoning of diverse phenotypes in trisomy 18 patients.

Potential Increased Risk of Trisomy 18 Observed After a Fertilizer Warehouse Fire in Brazos County and TX

Background: In this paper, we aimed to investigate the potential impacts of a fire accident in a fertilizer warehouse on chromosomal anomalies, including Trisomy 21 (T21) and Trisomy (T18) among pregnancies in Brazos County, Texas. We conducted an observational study in Brazos County, TX, with all patients of T18 and T21 cases in the live births in Brazos County between 2005–2014. The prevalence of T18 and T21 before, during, and after the accident in Brazos County were calculated and compared. The Standardized Morbidity Ratio (SMR) was applied to compare the prevalence of T18 and T21 in Brazos County to the statewide prevalence in Texas after adjusting for maternal race and age. Compared with statewide risk, the risk of T18 during the impacted years in Brazos county was found to be significantly higher (SMR = 5.0, 95% Confidence Interval(CI): 2.19–9.89), while there was no significant difference before (SMR = 0.77, 0.13–2.54) and after the accident (SMR = 0.71, 0.12–2.36). However, the prevalence of T21 during the impacted years was not significantly different from those before or after the accident. This study conclusively suggests that this fertilizer fire may be related to the increased prevalence of T18 in Brazos County, though the findings warrant further investigation.

The use of foetal ovarian stromal cell culture for cytogenetic diagnosis. Stromal ovarian culture cytogenetic diagnosis

Some studies have been carried out to analyze human female first meiotic prophase. Most of them use samples from foetuses collected after legal interruption of pregnancy. In some cases, a control population is needed and foetuses aborted for non-chromosomal reasons are used. The assumption of these samples as being euploids could perhaps represent an error. In this article, we describe an easy methodology to certify the euploidy of foetal ovarian tissue using an one-week somatic culture. Using this protocol, we have obtained a primary culture in 88.2% of the studied cases, material usable for being karyotyped in 93.3% of the cases, and a cytogenetic diagnosis was performed in 100% of these cases. Finding the same karyotype in cultured cells in cases in which we had a prenatal cytogenetic diagnosis has validated the technique, and in applying this protocol we have been able to check our prophase meiotic-study control population.

First report of a partial trisomy 3q12-q23 de novo--FISH breakpoint determination and phenotypic characterization

We present a 1-year-old boy with mild mental retardation, postnatal growth retardation, and facial dysmorphisms such as frontal bossing, laterally accentuated bushy eyebrows, deep set eyes with long lashes, hypertelorism, and a broad nasal bridge. Except for hip dysplasia, no congenital malformations were detected. By conventional cytogenetics a derivative chromosome 3 de novo was diagnosed which was identified as tandem dup(3)(q12q23) by fluorescence in situ hybridization (FISH) applying arm specific paints and eight different YAC-probes. The duplicated segment lies proximally from the reported dup(3q) syndrome critical region, thus explaining the absence of characteristic phenotypic features of dup(3q) syndrome. To our knowledge this is the first report of a patient with pure trisomy of this proximal region of the long arm of chromosome 3.

A comparison of maternal age, sex ratio and associated major anomalies among fetal trisomy 18 cases with different cell division of error

OBJECTIVES

To compare the maternal age, sex ratio, and associated major anomalies among fetal trisomy 18 cases with different cell division of error.

METHODS

Thirty-one consecutive cases of fetal trisomy 18 detected perinatally during a period of 6 years were studied. Among these, 18 were 47,XY,+18, and 13 were 47,XX,+18. The average gestational age at diagnosis was 19.7 +/- 4.6 weeks, and the maternal age at diagnosis was 34.5 +/- 5.8 years. DNA polymorphism analysis was applied to determine the parental origin, stage of non-disjunctional error and recombination.

RESULTS

Twenty-eight cases were of maternal origin. Among these, 20 had major anomalies, 17 had meiosis II (MII) errors, 10 had meiosis I (MI) errors, and one had a postzygotic mitotic (PZM) or non-crossover MII error. Three cases were of paternal origin. Among these, two had major anomalies, two had MI errors, and one had a PZM or non-crossover MII error. For the 17 cases with maternal MII errors, the average maternal age was 34.5 +/- 6.6 years. Of these cases, 12 had major anomalies, 13 were male, and 4 were female, giving a male:female sex ratio of 3.25:1. For the 10 cases with maternal MI errors, the average maternal age was 34.8 +/- 5.7 years. Of these cases, seven had major anomalies, three were male, and seven were female, giving a male:female sex ratio of 0.429:1.

CONCLUSION

In trisomy 18, there is a male preponderance in the fetuses caused by maternal MII errors and a female preponderance in the fetuses caused by maternal MI errors. No significant difference was noted in maternal age or in associated major anomalies between the two groups of maternal MII errors and maternal MI errors. No significant difference was noted in associated major anomalies between the maternal and paternal cases.

Molecular characterization of 18p deletions: evidence for a breakpoint cluster

PURPOSE

To determine the size and parental origin of the deletion in individuals with 18p- syndrome.

METHODS

Molecular and fluorescence in situ hybridization analyses of the pericentromeric region of chromosome 18 were performed on genomic DNA and chromosomes from study participants.

RESULTS

The majority of the breakpoints were located between markers D18S852 on 18p and D18S1149 on 18q, a distance of approximately 4 Mb. The parental origin of these deletions appears to be equally distributed, half maternally derived and half paternally derived.

CONCLUSION

The distributions of both the size and parental origin of the 18p deletions support the presence of a breakpoint cluster in the 18p- syndrome.

High frequency of XY disomy in spermatozoa of severe oligozoospermic men

Frequencies of disomy and diploidy in spermatozoa for chromosomes X, Y and 18 were compared among severe oligozoospermic men (<5x10(6) spermatozoa/ml), oligozoospermic men (5-20x10(6) spermatozoa/ml), and normospermic men using three-colour fluorescence in-situ hybridization (FISH). Semen samples were collected from 10 severe oligozoospermic men aged 26-49 years, 10 oligozoospermic men aged 27-48 years and seven normospermic men aged 25-31 years. Karyotypes in lymphocytes obtained from peripheral blood were all 46,XY. In severe oligozoospermic men, analysis of 200 interphases per individual using FISH showed XY constitutions for sex chromosomes in all cells. A minimum of 10 000 sperm nuclei per individual for each chromosome was evaluated in severe oligozoospermic men and oligozoospermic men, and a minimum of 6000 sperm nuclei per individual in normospermic men. In total, 245 707 sperm nuclei were evaluated. The hybridization efficiency was 99.8%. The severe oligozoospermic men showed significantly higher frequencies of XY disomy (0.41%) and diploidy (0.49%) compared with oligozoospermic men (0.16%, P < 0.01; 0.22%, P < 0.05) and normospermic men (0.18%, P < 0.05; 0.21%, P < 0.05) (Mann-Whitney U-test). The data suggest that when severe oligozoospermic men undergo intracytoplasmic sperm injection, there can be an increase in the rate of conceptuses with 47,XXY chromosomes.

Incidence of sperm aneuploidy in relation to semen characteristics and assisted reproductive outcome

OBJECTIVE

To evaluate the incidence of sperm aneuploidy in men screened for infertility and identify any eventual relation with assisted reproductive outcome.

DESIGN

Controlled prospective study.

SETTING

University hospital-based IVF program.

PATIENT(S)

Infertile couples who were screened for sperm aneuploidy and evaluated for IVF treatment.

INTERVENTION(S)

Fluorescence in situ hybridization was used to identify chromosomes 18, 21, X, and Y. The assisted reproductive techniques of IVF and intracytoplasmic sperm injection were used for infertility treatment.

MAIN OUTCOME MEASURE(S)

The incidence of sperm aneuploidy, semen parameters, fertilization rate, pregnancy characteristics, and rate of neonatal malformations were determined.

RESULT(S)

Oligozoospermic and teratozoospermic men had a significantly higher incidence of chromosomal abnormalities than men with normal semen parameters (2.7% vs. 1.8%). The increased frequency of sperm aneuploidy did not appear to affect pregnancy losses or the occurrence of neonatal malformations.

CONCLUSION(S)

Suboptimal semen samples had a higher incidence of aneuploidy. In this study, the increased frequency of chromosomal abnormalities did not have a direct effect on the fertilization rate, pregnancy characteristics, or neonatal outcome.

Aneuploidy in sperm and exposure to fungicides and lifestyle factors. ASCLEPIOS. A European Concerted Action on Occupational Hazards to Male Reproductive Capability

Fungicides include chemicals that are known aneugens. The purpose of the present study was to investigate whether occupational exposure to these and other agricultural pesticides induces aneuploidy in human sperm. The contribution of lifestyle factors (smoking and alcohol consumption) to the frequency of aneuploid sperm was evaluated as well. The effects of age and sperm concentration were analyzed as confounders. Spermatozoa from 30 healthy farmers were studied before and after exposure to fungicides, using fluorescence in situ hybridization (FISH). Ten thousand spermatozoa were scored per semen sample to determine the disomy and diploidy frequencies for chromosomes 1 and 7. Exposure to fungicides was not associated with sperm aneuploidy. Smoking was significantly associated with sperm carrying an extra chromosome 1 and with diploid sperm as well as with the aggregate frequency of aneuploid sperm. Alcohol consumption, sperm concentration, and age showed inconsistent results before and after the season of exposure to fungicides. For low-level exposures, such as occupational exposures, the sensitivity of the sperm-FISH method may not be sufficient. The present study supports earlier ones showing that smoking can increase aneuploidy in human sperm.

Genetics of oocyte ageing

OBJECTIVES

Correlations between parental age, aneuploidy in germ cells and recent findings on aetiological factors in mammalian trisomy formation are reviewed.

METHODS

Data from observations in human oocytes, molecular studies on the origin of extra chromosomes in trisomies, experiments in a mouse model system, and transgenic approaches are shown.

RESULTS

Errors in chromosome segregation are most frequent in meiosis I of oogenesis in mammals and predominantly predispose specific chromosomes and susceptible chiasmate configurations to maternal age-related nondisjunction. Studies on spindle structure, cell cycle and chromosome behaviour in oocytes of the CBA/Ca mouse used as a model for the maternal age-effect suggest that hormonal homeostasis and size of the follicle pool influence the quality, maturation competence and spindle size of the mammalian oocyte. Predisposition to errors in chromosome segregation are critically dependent on altered cell cycles. Compromised protein synthesis and mitochondrial function affect maturation kinetics and spindle formation, and cause untimely segregation of chromosomes (predivision), mimicking an aged phenotype.

CONCLUSIONS

Altered cell cycles and untimely resolution of chiasmata but also nondisjunction of late segregating homologues caused by asynchrony in cytoplasmic and nuclear maturation appear to be causal to errors in chromosome segregation with advanced maternal age. Oocytes appear to lack checkpoints guarding against untimely chromosome segregation. Genes and exposures affecting pool size, hormonal homeostasis and interactions between oocytes and their somatic compartment and thus quality of follicles and oocytes have the potential to critically influence chromosome distribution in female meiosis and affect fertility in humans and other mammals.

Rapid determination of trisomy 18 parental origin using fluorescent PCR and small tandem repeat markers: case reports

Trisomy 18 is the second most common genetic defect after trisomy 21, almost 90% of which are due to additional chromosome from the mother. The parental origin of the additional chromosome can, if required, be determined by two methods: karyotyping, which takes several weeks; or, more recently, by polymerase chain reaction (PCR) which is often problematic. Fluorescent PCR of small tandem repeats (STRs) can determine the parental origin in the majority of cases within 5 h. Although the incidence of paternal origin is known for both trisomy 21 and trisomy 18, this technique can rapidly determine the parental origin in cases where there is insufficient samples to perform conventional tests. Determining parental origin by these methods may also have clinical significance in the diagnosis of chromosomal translocations or in the diagnosis of genetic disease using linkage analysis.

Preferential loss of the paternal alleles in the 18q- syndrome

Individuals with the 18q- syndrome have variable deletions from the long arm of chromosome 18. They also exhibit a highly variable phenotype. To correlate genotype with phenotype accurately, extensive molecular and phenotypic analyses are needed on each affected individual. As a part of this analysis, we have determined the parental origin of the deleted chromosome in 34 individuals with the 18q- syndrome. We have found that 85% of the de novo deletions are paternal in origin. The percentage of fathers of individuals with paternally derived deletions who were > 30 years old was (not significantly) greater than that of the general population. The mothers of individuals with maternally derived deletions were near an average age for childbearing compared to the general population. Individuals with maternally derived terminal deletions had breakpoints as varied as those with paternally derived deletions. These results are consistent with the hypothesis that the reduced incidence of maternally derived deletions is not due to reduced viability, since individuals with large maternally derived deletions of chromosome 18q were found. We hypothesize that the prevalence of paternally derived deletions is due to an increased frequency of chromosome breakage in male germ cells. These results are consistent with results observed in other segmental aneusomies in which there is a high incidence of paternally derived deletions.

Trisomy of human chromosome 18: molecular studies on parental origin and cell stage of nondisjunction

We investigated the parent and cell division of origin of the extra chromosome 18 in 62 aneuploids with a free trisomy 18 by using chromosome-18-specific pericentromeric short-sequence repeats. In 46 cases, DNA of patients was recovered from archival specimens, such as paraffin-embedded tissues and fixed chromosomal spreads. In 56 families, the supernumerary chromosome was maternal in origin; in six families, it was paternal. Among the 56 maternally derived aneuploids, we could exclude a postzygotic mitotic error in 52 cases. Among those in which the nondisjunction was attributable to an error at meiosis, 11 were the result of a meiosis I nondisjunction and 17 were caused by a meiosis II error. This result differs markedly from findings in acrocentric chromosomes where nondisjunction at maternal meiosis I predominates. Among the six paternally derived cases, two originated from a meiotic error, indicating that a nondisjunction in paternal meiosis is not as rare as previously suggested.

Molecular studies of translocations and trisomy involving chromosome 13

Twenty-four cases of trisomy 13 and one case with disomy 13, but a de novo dic(13,13) (p12p12) chromosome, were examined with molecular markers to determine the origin of the extra (or rearranged) chromosome. Twenty-one of 23 informative patients were consistent with a maternal origin of the extra chromosome. Lack of a third allele at any locus in both paternal origin cases indicate a somatic duplication of the paternal chromosome occurred. Five cases had translocation trisomy: one de novo rob(13q14q), one paternally derived rob(13q14q), two de novo t(13q13q), and one mosaic de novo t(13q13q)/r(13). The patient with a paternal rob(13q14q) had a maternal meiotic origin of the trisomy; thus, the paternal inheritance of the translocation chromosome was purely coincidental. Since there is not a significantly increased risk for unbalanced offspring of a t(13q14q) carrier and most trisomies are maternal in origin, this result should not be surprising; however, it illustrates that one cannot infer the origin of translocation trisomy based on parental origin of the translocation. Lack of a third allele at any locus in one of the three t(13q13q) cases indicates that it was most likely an isochromosome of postmeiotic origin, whereas the other two cases showed evidence of recombination. One balanced (nontrisomic) case with a nonmosaic 45, -13, -13, +t(13;13) karyotype was also investigated and was determined to be a somatic Robertsonian translocation between the maternal and paternal homologues, as has been found for all balanced homologous Robertsonian translocations so far investigated. Thus, it is also incorrect to assume in de novo translocation cases that the two involved chromosomes are even from the same parent. Despite a maternal origin of the trisomy, we cannot therefore infer anything about the parental origin of the chromosomes 13 and 14 involved in the translocation in the de novo t(13q14q) case nor for the two t(13;13) chromosomes showing a meiotic origin of the trisomy.

Parental age-related aneuploidy in human germ cells and offspring: a story of past and present

Parental age is the most important aetiological factor in trisomy formation in humans. Cytogenetic studies on germ cells reviewed here imply that (i) 2-4% sperm are aneuploid and 8.6% oocytes from IVF are hyperploid (ii) a paternal age effect may exist, and (iii) oocytes of aged women contain precociously separated chromatids in metaphase II. Trisomy data suggest that most aneuploidy is generated during meiosis I of oogenesis and is maternal age-dependent. Trisomy 18 is unique, originating mostly from maternal meiosis II errors. The extra gonosome in 47, XXY derives mostly from a paternal meiosis I error. Trisomy of individual chromosomes may remain low, linearly rise, or exponentially increase with advanced maternal age. Maternal age related trisomies involve achiasmatic and normochiasmate chromosomes, and chromosomes with disturbed recombination and distally located chiasmata. Hypotheses on the origin of the maternal age effect are critically reviewed. One model is presented that relates to altered cell cycle and protein phosphorylation in oocytes of aged mammals and accounts for most of the observed data in humans and in experimental studies. Aneuploidy may thus involve a predetermined component but is possibly also influenced by extrinsic factors reducing oocyte quality or depleting the oocyte pool precociously. Areas of future research are proposed to elucidate (i) the significance of early disturbances in the prenatal ovary, (ii) parameters diminishing the quality of oocytes in dictyate stage, and (iii) mechanisms enabling oocytes to process all chromosomal configurations successfully during later stages of oogenesis. Studies with newly developed and existing animal models appear indispensable to identify exposures affecting chromosome disjunction during meiosis, especially in the aging female.