Risk factors for nondisjunction of trisomy 21

Detection of paternal origin of fetal trisomy 21 in a pregnancy with isolated ventriculomegaly but without advanced parental age

OBJECTIVE

We present detection of paternal origin of fetal trisomy 21 in a pregnancy with isolated ventriculomegaly but without advanced parental age.

CASE REPORT

A 29-year-old pregnant woman was admitted to the hospital at 18 weeks of gestation for tocolytic treatment because of irregular uterine contractions. Her husband was 30 years old. The couple had a healthy daughter. Prenatal ultrasound incidentally found isolated ventriculomegaly, and subsequent amniocentesis revealed a karyotype of 47,XX,+21 in 20/20 colonies of cultured amniocytes. The pregnancy was terminated, and the fetus manifested characteristic craniofacial appearance of Down syndrome and hyposplastic middle phalanx of the fifth finger. Postnatal polymorphic DNA marker analysis on the DNAs extracted from the cord blood and parental bloods using quantitative fluorescent polymerase chain reaction (QF-PCR) showed a paternal origin of fetal trisomy 21. The father had a karyotype of 46, XY in 40/40 blood lymphocytes.

CONCLUSION

QF-PCR is useful for rapid confirmation of prenatally detected fetal trisomy 21 and determination of paternal origin of fetal trisomy 21 especially in pregnancies with fetal structural abnormalities but without advanced parental age.

Double aneuploidy 48,ХХХ,+21 of a Bulgarian newborn with Down phenotype: a case report

Background

Aneuploidy is one of the most important chromosomal aberrations, which involves an abnormal number of the chromosomes. Trisomy 21 (Down syndrome) and numerical aberrations of the sex chromosomes have a relatively high prevalence in the general population. However, the patients usually have one of the above genetic disorders and combined cases of two different trisomies are unusual.

Case presentation

We report a case of a patient with double aneuploidy—a combination of trisomy 21 and triple X syndrome. The proband had typical features of Down syndrome and did not manifest any symptoms of polysomy X. The patient had hypotonia, a cardiac defect, and an annular pancreas. A clinical diagnosis of Down syndrome was established, but the cytogenetic analysis found two free full trisomies—trisomy 21 (Down syndrome) and triple X.

Conclusion

Cases of double aneuploidy, combining trisomy 21 and trisomy of a sex chromosome, could be challenging because the patients manifest only symptoms, typical for Down syndrome. The discovery of a second complete free trisomy X in our case was an incidental finding. This illustrates the importance of the cytogenetic analysis, despite the evident phenotype of trisomy 21.

Advanced paternal age: effects on sperm parameters, assisted reproduction outcomes and offspring health

Many factors, including postponement of marriage, increased life expectancy, and improved success with assisted reproductive technologies have been contributing to increased paternal age in developed nations. This increased average paternal age has led to concerns about adverse effects of advanced paternal age on sperm quality, assisted reproductive outcomes, and the health of the offspring conceived by older fathers. This review discusses the association between advanced paternal age and sperm parameters, assisted reproduction success rates, and offspring health.

Down syndrome with co-occurring Marfan syndrome

Down syndrome (DS) and Marfan syndrome (MFS) are two unique genetic disorders that share limited phenotypic overlap. There are very few reported cases in the existing literature on overlapping DS and MFS. Although these two disorders are phenotypically unique, features present in these cases are variable, resulting in mixed and dominant expressions of particular features. We present the first adolescent case of trisomy 21 associated DS and fibrillin-1 gene associated MFS in the literature who had a height at 90th percentile for an 11-year old boy and discuss the implications of this case in terms of future medical care when these two genetic syndromes are present in the same individual. Understanding of certain features of the ‘non-dominating’ syndrome is crucial for clinicians to recognise when DS co-occurs with MFS. Close monitoring of the cardiovascular, ophthalmologic and musculoskeletal systems is recommended if both syndromes are diagnosed given that both can be independently associated with disorders in these organ systems.

Gain of chromosome 21 in hematological malignancies: lessons from studying leukemia in children with Down syndrome

Structural and numerical alterations of chromosome 21 are extremely common in hematological malignancies. While the functional impact of chimeric transcripts from fused chromosome 21 genes such as TEL-AML1, AML1-ETO, or FUS-ERG have been extensively studied, the role of gain of chromosome 21 remains largely unknown. Gain of chromosome 21 is a frequently occurring aberration in several types of acute leukemia and can be found in up to 35% of cases. Children with Down syndrome (DS), who harbor constitutive trisomy 21, highlight the link between gain of chromosome 21 and leukemogenesis, with an increased risk of developing acute leukemia compared with other children. Clinical outcomes for DS-associated leukemia have improved over the years through the development of uniform treatment protocols facilitated by international cooperative groups. The genetic landscape has also recently been characterized, providing an insight into the molecular pathogenesis underlying DS-associated leukemia. These studies emphasize the key role of trisomy 21 in priming a developmental stage and cellular context susceptible to transformation, and have unveiled its cooperative function with additional genetic events that occur during leukemia progression. Here, using DS-leukemia as a paradigm, we aim to integrate our current understanding of the role of trisomy 21, of critical dosage-sensitive chromosome 21 genes, and of associated mechanisms underlying the development of hematological malignancies. This review will pave the way for future investigations on the broad impact of gain of chromosome 21 in hematological cancer, with a view to discovering new vulnerabilities and develop novel targeted therapies to improve long term outcomes for DS and non-DS patients.

A male Down syndrome with two normal boys: Cytogenetic, paternity and andrological investigations

Down syndrome is the most common autosomal chromosome anomaly with several medical abnormalities and intellectual disability, occurring in about of 1:1,000 to 1:1,100 infants. Many pregnancies in women with Down syndrome produce children both with normal and with trisomy 21, whereas males are infertile. However, Down syndrome males are not always infertile and this is not global. Here we reported a 36-year-old man with proved nonmosaic trisomy 21 fathered two normal boys. Paternity analysis using 26 microsatellite loci confirmed that Down syndrome male is the biological father of his two normal boys. Serum LH, FSH, testosterone and 17-OH progesterone were all in the normal range in this father with Down syndrome. To the best of our knowledge, this is the second report of one man with Down syndrome who has two normal children in the world. The current study not only supports the rare evidence of the fertility of males with Down syndrome but also highlights the caution in advising people responsible for the care of adults with this condition about possible fertility and transmission of sexual diseases as well.

Exposure to Latent Tuberculosis Treatment during Pregnancy. The PREVENT TB and the iAdhere Trials

RATIONALE

Data are limited regarding the safety of 12-dose once-weekly isoniazid (H, 900 mg) plus rifapentine (P, 900 mg) (3HP) for latent infection treatment during pregnancy.

OBJECTIVES

To assess safety and pregnancy outcomes among pregnant women who were inadvertently exposed to study medications in two latent tuberculosis infection trials (PREVENT TB or iAdhere) evaluating 3HP and 9 months of daily isoniazid (H, 300 mg) (9H).

METHODS

Data from reproductive-age (15-51 yr) women who received one or more study dose of 3HP or 9H in either trial were analyzed. Drug exposure during pregnancy occurred if the estimated date of conception was on or before the last dose date.

RESULTS

Of 126 pregnancies (125 participants) that occurred during treatment or follow-up, 87 were exposed to study drugs. Among these, fetal loss was reported for 4/31 (13%) and 8/56 (14%), 3HP and 9H, respectively (difference, 13% - 14% = -1%; 95% confidence interval = -17% to +18%) and congenital anomalies in 0/20 and 2/41 (5%) live births, 3HP and 9H, respectively (difference, 0% - 5% = -5%; 95% confidence interval = -18% to +16%). All fetal losses occurred in pregnancies of less than 20 weeks. Of the total 126 pregnancies, fetal loss was reported in 8/54 (15%) and 9/72 (13%), 3HP and 9H, respectively; and congenital anomalies in 1/37 (3%) and 2/56 (4%) live births, 3HP and 9H, respectively. The overall proportion of fetal loss (17/126 [13%]) and anomalies (3/93 [3%]) were similar to those estimated for the United States, 17% and 3%, respectively.

CONCLUSIONS

Among reported pregnancies in these two latent tuberculosis infection trials, there was no unexpected fetal loss or congenital anomalies. These data offer some preliminary reassurance to clinicians and patients in circumstances when these drugs and regimens are the best option in pregnancy or in women of child-bearing potential. This work used the identifying trial registration numbers NCT00023452 and NCT01582711, corresponding to the primary clinical trials PREVENT TB and iAdhere (Tuberculosis Trials Consortium Study 26 and 33).

Parental age and child outcomes

This review summarizes the impact of parental age on children's health outcomes beyond the perinatal period. In the last decades, delayed parenthood with both men and women has become a public health issue. For women, in particular, the size of this delay is substantial. For a few medical conditions, older parental age has a pronounced effect on child morbidity. For most other outcomes, a more modest effect is evident. Although these effects might be limited on an individual level, they have a substantial impact at the level of population health.

Fetopathological examination for the fetuses with Down syndrome in Tunisia: Epidemiological study and associated malformations

BACKGROUND

For Down syndrome (DS), traditional epidemiological studies to determine the prevalence, cause, and clinical significance of the syndrome have been conducted over the last 100 years. In Tunisia, the current work is the first in-depth study in epidemiology of DS from fetopathological data.

AIM OF THE STUDY

The aim of this epidemiological study was to determine the impact of some feto-maternal characteristics in occurrence of DS and to search the frequency of associated congenital malformations with this syndrome.

METHODS

Our retrospective study was realized for 144 fetuses with DS among 9321 autopsied fetuses in embryo-fetopathological service between 1994 and 2011.

RESULTS

In our study, the majority of mothers (72.91%) were 35 years and older, with a statistically significant difference (p<10^-6, OR=16.7, CI=8.7-32.4). The abnormalities of extremities (31%) were the most common fetal abnormalities followed by facial (23.51%) and digestive abnormalities (19.63%).

CONCLUSION

One of the main conclusions of this research is that the most common risk factor for DS is maternal age. On the other hand, the type and the frequency of associated congenital anomalies with DS are still controversial.

The importance of understanding individual differences in Down syndrome

In this article, we first present a summary of the general assumptions about Down syndrome (DS) still to be found in the literature. We go on to show how new research has modified these assumptions, pointing to a wide range of individual differences at every level of description. We argue that, in the context of significant increases in DS life expectancy, a focus on individual differences in trisomy 21 at all levels-genetic, cellular, neural, cognitive, behavioral, and environmental-constitutes one of the best approaches for understanding genotype/phenotype relations in DS and for exploring risk and protective factors for Alzheimer's disease in this high-risk population.

Mosaicism for trisomy 21: a review

The clinical and cytogenetic findings associated with mosaicism for trisomy 21/Down syndrome are the focus of this review. The primary topics discussed in this overview of the extant literature include the history of this condition and its diagnosis, the incidence of mosaicism, the meiotic and/or mitotic chromosomal malsegregation events resulting in mosaicism, the observation of mosaicism in the parents of children with the non-mosaic form of Down syndrome, and the variation in phenotypic outcome for both constitutional and acquired traits present in people with mosaicism for trisomy 21/Down syndrome, including cognition, fertility, and overall phenotypic findings. Additional topics reviewed include the social conditions of people with mosaicism, as well as age-related and epigenetic alterations observed in people with mosaicism for trisomy 21/Down syndrome. .

Seasonality of fetal trisomy 21--have ambient air pollutants played a role?

OBJECTIVE

To examine the seasonality of fetal trisomy 21 and its relationship with ambient air pollutants.

METHODS

The averaged incidence by month-of-conception of the 113 cases (2002-2009) in our registry was correlated with month of conception and monthly ambient levels of nitrogen oxides (NOx, NO and NO2), sulfur dioxide, carbon monoxide, and ozone as reported by the Hong Kong Environmental Protection Department at the month of, and four-week after, conception.

RESULTS

The incidence was highest in February (3.45/1000 births) and lowest in October (1.28/1000 births), and showed a significant difference (p = 0.003) and positive correlation (p = 0.003) from winter to autumn. It was also correlated with NO (p = 0.017) and inversely with ozone (p = 0.014) at conception.

CONCLUSIONS

Seasonal variation in incidence of fetal trisomy 21 was correlated with ambient levels of nitric oxides and ozone. The role of environmental pollutants on fetal aneuploidy warrants further investigation.

Amino acid turnover by human oocytes is influenced by gamete developmental competence, patient characteristics and gonadotrophin treatment

STUDY QUESTION

Can amino acid profiling differentiate between human oocytes with differing competence to mature to metaphase II (MII) in vitro?

SUMMARY ANSWER

Oocytes which remained arrested at the germinal vesicle (GV) stage after 24 h of in vitro maturation (IVM) displayed differences in the depletion/appearance of amino acids compared with oocytes which progressed to MII and patient age, infertile diagnosis and ovarian stimulation regime significantly affected oocyte amino acid turnover during IVM.

WHAT IS KNOWN ALREADY

Amino acid profiling has been proposed as a technique which can distinguish between human pronucleate zygotes and cleavage stage embryos with the potential to develop to the blastocyst stage and implant to produce a pregnancy and those that arrest. Most recently, the amino acid turnover by individual bovine oocytes has been shown to be predictive of oocyte developmental competence as indicated by the gamete's capacity to undergo fertilization and early cleavage divisions in vitro.

STUDY DESIGN, SIZE, DURATION

The study was conducted between March 2005 and March 2010. A total of 216 oocytes which were at the GV or metaphase I (MI) stages at the time of ICSI were donated by 67 patients.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

The research was conducted in university research laboratories affiliated to a hospital-based infertility clinic. Oocytes were cultured for 24 h and the depletion/appearance of amino acids was measured during the final 6 h of IVM. Amino acid turnover was analysed in relation to oocyte meiotic progression, patient age, disease aetiology and controlled ovarian stimulation regime.

MAIN RESULTS AND THE ROLE OF CHANCE

The depletion/appearance of key amino acids was linked to the maturation potential of human oocytes in vitro. Oocytes which arrested at the GV stage (n = 9) depleted significantly more valine and isoleucine than those which progressed to MI (n = 32) or MII (n = 107) (P < 0.05). Glutamate, glutamine, arginine and valine depletion or appearance differed in MII versus degenerating oocytes (n = 20) (P < 0.05). Glutamine, arginine, methionine, phenylalanine, total depletion and total turnover all differed in oocytes from patients aged < 35 years versus patients ≥35 years (P < 0.05). MII oocytes obtained following ovarian stimulation with recombinant FSH depleted more isoleucine (P < 0.05) and more alanine and lysine (P < 0.05) appeared than oocytes from hMG-stimulated cycles. MII oocytes from patients with a polycystic ovary (PCO) morphology (n = 33) depleted more serine (P < 0.05) than oocytes from women with normal ovaries (n = 61).

LIMITATIONS, REASONS FOR CAUTION

Immature oocytes collected at the time of ICSI were used as the model for human oocyte maturation. These oocytes have therefore failed to respond to the ovulatory hCG trigger in vivo (they are meiotically incompetent), and have limited capacity to support embryo development in vitro. The lack of cumulus cells and stress of the conditions in vitro may have influenced turnover of amino acids, and owing to the small sample sizes further studies are required to confirm these findings.

WIDER IMPLICATIONS OF THE FINDINGS

The findings provide support for the hypothesis that oocyte metabolism reflects oocyte quality. Longitudinal studies are required to link these functional metabolic indices of human oocyte quality with embryo developmental competence. Oocyte amino acid profiling may be a useful tool to quantify the impact of new assisted reproduction technologies (ART) on oocyte quality.

STUDY FUNDING/COMPETING INTERESTS

This project was funded by the UK Biology and Biotechnology Research Council (BB/C007395/1) and the Medical Research Council (G 0800250). K.E.H was in receipt of a British Fertility Society/Merck Serono studentship. H.J.L. is a shareholder in Novocellus Ltd, a company which seeks to devise a non-invasive biochemical test of embryo health.

The proportion of uniparental disomy is increased in Prader-Willi syndrome due to an advanced maternal childbearing age in Korea

Prader-Willi syndrome (PWS) is a genetic disorder caused by the absence of expression of the paternal copy of maternally imprinted genes in chromosome region 15q11-13. The genetic subtypes of PWS are classified into deletion (~70%), maternal uniparental disomy (mUPD; 25-30%), imprinting center defects (3-5%) and rare unbalanced translocations. Recently, Matsubara et al. reported a significantly higher maternal age in a trisomy rescue (TR) or gamete complementation (GC) by nondisjunction at maternal meiosis 1 (M1) group than in a deletion group. In the present study, we try to confirm their findings in an ethnically different population. A total of 97 Korean PWS patients were classified into deletional type (n=66), TR/GC (M1) (n=15), TR/GC by nondisjunction at maternal meiosis 2 (n=2), monosomy rescue or postfertilization mitotic nondisjunction (n=4) and epimutation (n=2). Maternal ages at birth showed a significant difference between the deletion group (median age of 29, interquartile range (IQR)=(27,31)) and the TR/GC (M1) group (median age of 35, IQR=(31,38)) (P<0.0001). The relative birth frequency of the TR/GC (M1) group has substantially increased since 2006 when compared with the period before 2005. These findings support the hypothesis that the advanced maternal age at childbirth is a predisposing factor for the development of mUPD because of increased M1 errors.

Molecular basis of maternal age-related increase in oocyte aneuploidy

Aneuploidy is one of the most common and serious pregnancy complications in humans. Most conceptuses with autosomal aneuploidy die in utero, resulting in early pregnancy loss. However, some fetuses with aneuploidy survive to term but suffer from disorders associated with congenital anomalies and mental retardation, such as Down syndrome with trisomy 21. Three general characteristics of this condition are well acknowledged: (i) in most cases the extra chromosome is of maternal origin; (ii) most cases are derived from a malsegregation event in meiosis I; and (iii) the frequency of these errors increases with maternal age. The basis for the age-dependent increase in meiosis I errors has been a long-standing enigma. Many investigators have addressed the nature of this biological phenomenon through genomic analyses of extra chromosome 21 using polymorphic markers to determine the frequency or location of crossovers that should ensure faithful chromosome segregation. Cytogenetic analyses of in vitro unfertilized oocytes have also been performed. However, no definitive conclusions regarding meiosis I errors have yet been reached from such studies. Recent findings in conditional knock-out mice for meiosis-specific cohesin have shed further light on this issue. The present review focuses on the current understanding of age-related aneuploidy and provides an overview of the mechanisms involved. We refer to recent data to illustrate some of the new paradigms that have arisen in this field.

The high incidence of STR D21S1446 homozygosity in Han and She populations living in South Eastern China

PURPOSE

This study investigated the allelic frequency of 4 short terminal repeats (STRs) in Han and She populations from eastern China.

METHODS

DNA samples from Han (N = 110) and She (N = 110) healthy subjects were amplified using PCR and primers specific for the STRs. D21S11 and D21S1446 (chromosome 21) and D18S865 and D18S535 (chromosome 18). The frequency and homozygocity of different STRs were evaluated.

RESULTS

For both populations, D21S11 and D18S535 were more polymorphic than D21S1446 and D18S865, and the D21S1446 1 allele was very common (48.6% and 55.0% for the Han and She groups, respectively).The Han and She groups significantly differed from one another in respect to the distribution of D21S11, D18S865, and D18S535 allelic frequency (all P -values ≤ 0.48) but had a similar allelic distribution for D21S1446 (P = 0.106). D21S1446 was found to be homozygous about 50% of the time which was significantly greater compared to the other STRs analyzed.

CONCLUSION

This study found that the Han and She differ genetically at 3 autosomal STRs located on chromosome 18 and 21. The STR D21S1146 was often homozygous within these groups, indicating it would be poor marker for analyzing trisomy within these populations.

Down syndrome: parental origin, recombination, and maternal age

The aims of the present study were to assess (1) the parental origin of trisomy 21 and the stage in which nondisjunction occurs and (2) the relationship between altered genetic recombination and maternal age as risk factors for trisomy 21. The study included 102 cases with Down syndrome from the Croatian population. Genotyping analyses were performed by polymerase chain reaction using 11 short tandem repeat markers along chromosome 21q. The vast majority of trisomy 21 was of maternal origin (93%), followed by paternal (5%) and mitotic origin (2%). The frequencies of maternal meiotic I (MI) and meiotic II errors were 86% and 14%, respectively. The highest proportion of cases with zero recombination was observed among those with maternal MI derived trisomy 21. A higher proportion of telomeric exchanges were presented in cases with maternal MI errors and cases with young mothers, although these findings were not statistically significant. The present study is the first report examining parental origin and altered genetic recombination as a risk factor for trisomy 21 in a Croatian population. The results support that trisomy 21 has a universal genetic etiology across different human populations.

Chromosome 21 non-disjunction and Down syndrome birth in an Indian cohort: analysis of incidence and aetiology from family linkage data

We analysed the family linkage data obtained from short tandem repeat (STR) genotyping of 212 unrelated Indian families having a single Down syndrome (DS) baby each, in order to explore the incidence and aetiology of this human aneuploidy in our cohort. The estimated values of maternal meiotic I and meiotic II non-disjunction (NDJ) errors of chromosome 21 (Ch 21) were ~78 and ~22%, respectively. Within the paternal outcome group, about 47 and 53% were accounted for NDJ at meiosis I and meiosis II, respectively. We estimated only ~2% post-zygotic mitotic errors. The comparison of average age of conception between controls and DS-bearing mothers revealed a significant difference (P<0·001) with DS-bearing women were on an average older than controls and meiotic II non-disjoined mothers were oldest among meiotic outcome groups. Our linkage analysis suggested an overall reduction in recombination by more than 50% on meiotic I non-disjoined maternal Ch 21 with error prone to susceptible chiasma formation within the ~5·1 kbp segment near the telomeric end. We stratified meiotic I non-disjoined women in three age groups, viz. young (⩽28 years), middle (29–34 years) and old (⩾35 years) and found linear decrease in the frequency of achiasmate meiosis from the young to the old group. In contrary, a linear increase in the multiple chiasma frequency from the young to the old group was observed. Considering these results together, we propose that the risk factors for Ch 21 NDJ are of two types, one being ‘maternal age-independent’ and the other being ‘maternal age-dependent’. Moreover, a comparison of our present Indian dataset with that of other published data of ethnically different populations suggested that the genetics that underlies the NDJ of Ch 21 is probably universal irrespective of racial difference across human populations. The present study is the first population-based report on any DS cohort from the Indian subcontinent and our work will help future workers in understanding better the aetiology of this birth defect.

Retinopathy of prematurity and maternal age

PURPOSE

To determine the risk factors, especially maternal risk factors, associated with the development of retinopathy of prematurity (ROP) in premature babies.

METHODS

A matched case-control study involving premature patients was undertaken retrospectively. The case group consisted of premature babies with the subsequent development of ROP. The control group consisted of gestational age-matched and sex-matched premature babies that did not develop ROP during the follow-up period. Risk factors involving patient demographics and maternal characteristics were compared between the case and control groups.

RESULTS

A total of 144 patients were included in this study (72 patients in the case group and 72 patients in the control group). Among the 66 possible risk factors compared, only birth weight and maternal age were found to be significant risk factors. Birth weight was significantly lower in the case group (1,248.7 +/- 257.8 g vs. 1,335.5 +/- 297.2 g, P = 0.01), and maternal age was significantly older in the case group compared with that in the control group (31.2 +/- 5.1 years vs. 28.2 +/- 5.3 years, P < 0.001). The odds ratio of having babies with ROP was 2.9 when the maternal age was >30 years.

CONCLUSION

Older maternal age is a newly identified risk factor for the development of ROP in premature babies.

Germ-line transmission of trisomy 21: Data from 80 families suggest an implication of grandmaternal age and a high frequency of female-specific trisomy rescue

Background

Trisomy of chromosome 21 (T21; Down syndrome, DS) is the most common aneuploidy in live births. Though its etiology has been intensively studied for a half of century, there are surprisingly many problems awaiting their elucidation. Some of the open questions are related directly to germ line mosaicism for T21, other problems include the prevalence of males with non-mosaic trisomy over females (skewed sex ratio, SR), the genetic predisposition to non-disjunction, etc. Studies in families of gonadal mosaicism (GM) carriers might help resolving some of these problems.

Results

80 families of carriers of GM, in which the sex of the offspring had been specified, were identified in the literature and in logbooks of two local genetic units. Mothers in these families were relatively young: only 8% of mothers were 35 years old and older at the time of delivery of their first affected offspring while the proportion of grandmothers on the GM carrier's side aged 35 years old and older was significantly higher (39%). Postzygotic rescue of T21 due to error in the meiosis I had been proposed as a mechanism of parental GM formation in 78% of the families with known origin of the T21. For the other 22%, rescue of errors in the meiosis II or postzygotic mitotic non-disjunction was assumed. Mosaicism for T21 in successive generations was reported in at least 12 families. The proportion of mosaics among affected female offspring (14%) is significantly higher compared to that among affected male offspring (0%). Male preponderance (SR = 1.5) is found in non mosaic liveborn offspring with either maternally- or paternally transmitted T21. Among unaffected offspring of male carriers of GM there is a notable excess of females (SR = 0.27).

Conclusion

Both direct (results of cytogenetic and molecular study of the origin of trisomic line) and indirect (advanced grandmaternal age on the side of GM carrier) evidences allow to assume that significant proportion of the mosaic parents had been conceived as trisomics. Female-specific trisomy rescue and genetic predisposition to postzygotic non-disjunction has been suggested as mechanisms of formation of both GM and somatic mosaicism. Typical male preponderance in affected non mosaic offspring with either maternally- or paternally transmitted trisomy 21, indicates than meiotic events are not responsible for the skewed sex ratio in DS. However a female excess among unaffected offspring of male carriers of GM might be the result of meiotic non homologous co-orientation of chromosomes 21 and X in spermatogenesis.

Effects of age on meiosis in budding yeast

In humans, the frequency with which meiotic chromosome mis-segregation occurs increases with age. Whether age-dependent meiotic defects occur in other organisms is unknown. Here, we examine the effects of replicative aging on meiosis in budding yeast. We find that aged mother cells show a decreased ability to initiate the meiotic program and fail to express the meiotic inducer IME1. The few aged mother cells that do enter meiosis complete this developmental program but exhibit defects in meiotic chromosome segregation and spore formation. Furthermore, we find that mutations that extend replicative life span also extend the sexual reproductive life span. Our results indicate that in budding yeast, the ability to initiate and complete the meiotic program as well as the fidelity of meiotic chromosome segregation decrease with cellular age and are controlled by the same pathways that govern aging of asexually reproducing yeast cells.

Mutations of the SYCP3 gene in women with recurrent pregnancy loss

Aneuploidy, a chromosomal numerical abnormality in the conceptus or fetus, occurs in at least 5% of all pregnancies and is the leading cause of early pregnancy loss in humans. Accumulating evidence now suggests that the correct segregation of chromosomes is affected by events occurring in prophase during meiosis I. These events include homologous chromosome pairing, sister-chromatid cohesion, and meiotic recombination. In our current study, we show that mutations in SYCP3, a gene encoding an essential component of the synaptonemal complex that is central to the interaction of homologous chromosomes, are associated with recurrent pregnancy loss. Two out of 26 women with recurrent pregnancy loss of unknown cause were found to carry independent heterozygous nucleotide alterations in this gene, neither of which was present among a group of 150 fertile women. Analysis of transcripts from minigenes harboring each of these two mutations revealed that both affected normal splicing, possibly resulting in the production of C-terminally mutated proteins. The mutant proteins were found to interact with their wild-type counterpart in vitro and inhibit the normal fiber formation of the SYCP3 protein when coexpressed in a heterologous system. These data suggest that these mutations are likely to generate an aberrant synaptonemal complex in a dominant-negative manner and contribute to abnormal chromosomal behavior that might lead to recurrent miscarriage. Combined with the fact that similar mutations have been previously identified in two males with azoospermia, our current data suggest that sexual dimorphism in response to meiotic disruption occurs even in humans.

Maternal age and risk for trisomy 21 assessed by the origin of chromosome nondisjunction: a report from the Atlanta and National Down Syndrome Projects

We examined the association between maternal age and chromosome 21 nondisjunction by origin of the meiotic error. We analyzed data from two population-based, case-control studies: Atlanta Down Syndrome Project (1989-1999) and National Down Syndrome Project (2001-2004). Cases were live born infants with trisomy 21 and controls were infants without trisomy 21 delivered in the same geographical regions. We enrolled 1,215 of 1,881 eligible case families and 1,375 of 2,293 controls. We report four primary findings. First, the significant association between advanced maternal age and chromosome 21 nondisjunction was restricted to meiotic errors in the egg; the association was not observed in sperm or in post-zygotic mitotic errors. Second, advanced maternal age was significantly associated with both meiosis I (MI) and meiosis II (MII). For example, compared to mothers of controls, mothers of infants with trisomy 21 due to MI nondisjunction were 8.5 times more likely to be >or=40 years old than 20-24 years old at the birth of the index case (95% CI=5.6-12.9). Where nondisjunction occurred in MII, mothers were 15.1 times more likely to be >or=40 years (95% CI = 8.4-27.3). Third, the ratio of MI to MII errors differed by maternal age. The ratio was lower among women <19 years of age and those >or=40 years (2.1, 2.3, respectively) and higher in the middle age group (3.6). Lastly, we found no effect of grand-maternal age on the risk for maternal nondisjunction. This study emphasizes the complex association between advanced maternal age and nondisjunction of chromosome 21 during oogenesis.

Reproductive health of adolescent girls who carry the FMR1 premutation: expected phenotype based on current knowledge of fragile x-associated primary ovarian insufficiency

The fragile X mental retardation 1 (FMR1) gene, located on the X chromosome, is characterized by a dynamic CGG repeat expansion in the 5' untranslated region. It has long been known that female carriers of the FMR1 premutation allele (55-199 CGG) are at risk for passing the FMR1 full mutation (> or =200 repeats) to their offspring, which results in a common form of mental retardation known as fragile X syndrome. The FMR1 premutation allele, however, also places female carriers at significantly increased risk for prematurely diminished ovarian function, which we refer to as fragile X-associated primary ovarian insufficiency (FXPOI). Although of particular concern for younger women, to date, studies of FXPOI have been restricted to women > or =18 years of age and have not specifically addressed ovarian reserve and menstrual cycle characteristics among adolescent carriers. We discuss the expected reproductive phenotype among FMR1 premutation carriers during adolescence, the associated health considerations based on our current understanding of FXPOI, and the directions for future studies.

Ovarian reserve

As a result of temporary social trends, many women elect to postpone their first pregnancy to a later stage in life. A large part of this population will be infertile by the time they opt to conceive, mainly because of a decreasing ovarian reserve and low oocyte quality resulting from age. Aging oocytes have been widely suggested to be the major cause for the decline in fertility. In a subfertile population, the availability of an accurate screening test of ovarian reserve would provide a valuable means of predicting the chances of pregnancy and live birth with or without treatment and selecting an optimal dose of ovarian stimulation where treatment using ovarian stimulation is planned. The following hormonal markers and ultrasound parameters have been used to attempt to estimate ovarian reserve and predict those with a poor chance of success in assisted reproductive techniques: age; concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol, inhibin, anti-Müllerian hormone; ovarian volume, ovarian antral follicle count; and ovarian biopsy. Further studies have introduced the use of dynamic tests-using gonadotropin-releasing hormone agonist, FSH, or clomiphene citrate-to assess ovarian function. The use of a wide range of tests suggests that no single test provides a sufficiently accurate result. But the simultaneous evaluation of a combination of tests could be used as a marker of diminished ovarian reserve and a sensitive predictor of response to ovarian stimulation in patients undergoing in vitro fertilization treatment.

Statement on guidance for genetic counseling in advanced paternal age

In 1996, a practice guideline on genetic counseling for advanced paternal age was published. The current document updates the state of knowledge of advanced paternal age effects on single gene mutations, chromosome anomalies, and complex traits.

The association of folate, zinc and antioxidant intake with sperm aneuploidy in healthy non-smoking men

BACKGROUND

Little is known about the effect of paternal nutrition on aneuploidy in sperm. We investigated the association of normal dietary and supplement intake of folate, zinc and antioxidants (vitamin C, vitamin E and beta-carotene) with the frequency of aneuploidy in human sperm.

METHODS

Sperm samples from 89 healthy, non-smoking men from a non-clinical setting were analysed for aneuploidy using fluorescent in situ hybridization with probes for chromosomes X, Y and 21. Daily total intake (diet and supplements) for zinc, folate, vitamin C, vitamin E and beta-carotene was derived from a food frequency questionnaire. Potential confounders were obtained from a self-administered questionnaire.

RESULTS

After adjusting for covariates, men with high folate intake (>75th percentile) had lower frequencies of sperm with disomies X, 21, sex nullisomy, and a lower aggregate measure of sperm aneuploidy (P <or= 0.04) compared with men with lower intake. In adjusted continuous analyses, total folate intake was inversely associated with aggregate sperm aneuploidy (-3.6% change/100 microg folate; 95% CI: -6.3, -0. 8) and results were similar for disomies X, 21 and sex nullisomy. No consistent associations were found between antioxidant or zinc intakes and sperm aneuploidy.

CONCLUSIONS

Men with high folate intake had lower overall frequencies of several types of aneuploid sperm.

Meiosis in oocytes: predisposition to aneuploidy and its increased incidence with age

Mammalian oocytes begin meiosis in the fetal ovary, but only complete it when fertilized in the adult reproductive tract. This review examines the cell biology of this protracted process: from entry of primordial germ cells into meiosis to conception. The defining feature of meiosis is two consecutive cell divisions (meiosis I and II) and two cell cycle arrests: at the germinal vesicle (GV), dictyate stage of prophase I and at metaphase II. These arrests are spanned by three key events, the focus of this review: (i) passage from mitosis to GV arrest during fetal life, regulated by retinoic acid; (ii) passage through meiosis I and (iii) completion of meiosis II following fertilization, both meiotic divisions being regulated by cyclin-dependent kinase (CDK1) activity. Meiosis I in human oocytes is associated with an age-related high rate of chromosomal mis-segregation, such as trisomy 21 (Down's syndrome), resulting in aneuploid conceptuses. Although aneuploidy is likely to be multifactorial, oocytes from older women may be predisposed to be becoming aneuploid as a consequence of an age-long decline in the cohesive ties holding chromosomes together. Such loss goes undetected by the oocyte during meiosis I either because its ability to respond and block division also deteriorates with age, or as a consequence of being inherently unable to respond to the types of segregation defects induced by cohesion loss.

Epidemiology of Down syndrome

Down syndrome (DS) is the most commonly identified genetic form of mental retardation and the leading cause of specific birth defects and medical conditions. Traditional epidemiological studies to determine the prevalence, cause, and clinical significance of the syndrome have been conducted over the last 100 years. DS has been estimated to occur in approximately 1 in 732 infants in the United States, although there is some evidence that variability in prevalence of estimates exist among racial/ethnic groups. Progress has been made in characterizing the specific types of chromosome errors that lead to DS and in identifying associated factors that increase the risk of chromosome 21 malsegregation, i.e., advanced maternal age and recombination. Studies to examine the variability of the presence of specific DS-associated birth defects and medical conditions provide evidence for genetic and environmental modifiers. Here, we provide a brief survey of studies that address the current state of the field and suggest gaps in research that can soon be filled with new multidisciplinary approaches and technological advances.

Gender effects on the incidence of aneuploidy in mammalian germ cells

Aneuploidy occurs in 0.3% of newborns, 4% of stillbirths, and more than 35% of all human spontaneous abortions. Human gametogenesis is uniquely and gender-specific susceptible to errors in chromosome segregation. Overall, between 1% and 4% of sperm and as many as 20% of human oocytes have been estimated by molecular cytogenetic analysis to be aneuploid. Maternal age remains the paramount aetiological factor associated with human aneuploidy. The majority of extra chromosomes in trisomic offspring appears to be of maternal origin resulting from nondisjunction of homologous chromosomes during the first meiotic division. Differences in the recombination patterns between male and female meiosis may partly account for the striking gender- and chromosome-specific differences in the genesis of human aneuploidy, especially in aged oocytes. Nondisjunction of entire chromosomes during meiosis I as well as premature separation of sister chromatids or homologues prior to meiotic anaphase can contribute to aneuploidy. During meiosis, checkpoints at meiotic prophase and the spindle checkpoint at M-phase can induce meiotic arrest and/or cell death in case of disturbances in pairing/recombination or spindle attachment of chromosomes. It has been suggested that gender differences in aneuploidy may result from more permissive checkpoints in females than males. Furthermore, age-related loss of chromosome cohesion in oocytes as a cause of aneuploidy may be female-specific. Comparative data about the susceptibility of human male and female germ cells to aneuploidy-causing chemicals is lacking. Increases of aneuploidy frequency in sperm have been shown after exposure to therapeutic drugs, occupational agents and lifestyle factors. Conversely, data on oocyte aneuploidy caused by exogenous agents is limited because of the small numbers of oocytes available for analysis combined with potential maternal age effects. The vast majority of animal studies on aneuploidy induction in germ cells represent cause and effect data. Specific studies designed to evaluate possible gender differences in induction of germ cell aneuploidy have not been found. However, the comparison of rodent data available from different laboratories suggests that oocytes are more sensitive than male germ cells when exposed to chemicals that effect the meiotic spindle. Only recently, in vitro experiments, analyses of transgenic animals and knockdown of expression of meiotic genes have started to address the molecular mechanisms underlying chromosome missegregation in mammalian germ cells whereby striking differences between genders could be shown. Such information is needed to clarify the extent and the mechanisms of gender effects, including possible differential susceptibility to environmental agents.

Reproductive ageing in women

The traditional view in respect to female reproduction is that the number of oocytes at birth is fixed and continuously declines towards the point when no more oocytes are available after menopause. In this review we briefly discuss the embryonic development of female germ cells and ovarian follicles. The ontogeny of the hypothalamic-pituitary-gonadal axis is then discussed, with a focus on pubertal transition and normal ovulatory menstrual cycles during female adult life. Biochemical markers of menopausal transition are briefly examined. We also examine the effects of age on female fertility, the contribution of chromosomal abnormalities of the oocyte to the observed decline in female fertility with age and the possible biological basis for the occurrence of such abnormalities. Finally, we consider the effects of maternal age on obstetric complications and perinatal outcome. New data that have the potential to revolutionize our understanding of mammalian oogenesis and follicular formation, and of the female reproductive ageing process, are also briefly considered.

Adaptive-filtering of trisomy 21: risk of Down syndrome depends on family size and age of previous child

The neonatal incidence rate of Down syndrome (DS) is well-known to accelerate strongly with maternal age. This non-linearity renders mere accumulation of defects at recombination during prolonged first meiotic prophase implausible as an explanation for DS rate increase with maternal age, but might be anticipated from chromosomal drive (CD) for trisomy 21. Alternatively, as there is selection against genetically disadvantaged embryos, the screening system that eliminates embryos with trisomy 21 might decay with maternal age. In this paper, we provide the first evidence for relaxed filtering stringency (RFS) to represent an adaptive maternal response that could explain accelerating DS rates with maternal age. Using historical data, we show that the proportion of aberrant live births decrease with increased family size in older mothers, that inter-birth intervals are longer before affected neonates than before normal ones, and that primiparae exhibit elevated levels of DS incidence at higher age. These findings are predicted by adaptive RFS but cannot be explained by the currently available alternative non-adaptive hypotheses, including CD. The identification of the relaxation control mechanism and therapeutic restoration of a stringent screen may have considerable medical implications.

Changing rates of genetic subtypes of Prader-Willi syndrome in the UK

The genetically determined neurodevelopmental disorder, Prader-Willi syndrome (PWS), has two main genetic subtypes: a 15q11-q13 deletion affecting the paternally inherited chromosome 15 and chromosome 15 maternal uniparental disomy (mUPD) in which two maternal copies of chromosome 15 are inherited but no paternal copy. It has been accepted that these subtypes occur in approximately 70 and 25% of cases, respectively. This is the first report of a greater proportion (50%) of those with PWS due to mUPD in children presently under 5 years living in the UK. Increasing maternal age at conception is likely to explain the changing proportions in this generation of mothers.