Gestational loss and growth restriction by angiogenic defects in placental growth factor transgenic mice.

OBJECTIVE: Angiogenesis is an important biological process during development, reproduction, and in immune responses. Placental growth factor (PlGF) is a member of vascular endothelial growth factor that is critical for angiogenesis and vasculogenesis. We generated transgenic mice overexpressing PlGF in specifically T cells using the human CD2-promoter to investigate the effects of PlGF overexpression. APPROACH AND RESULTS: Transgenic mice were difficult to obtain owing to high lethality; for this reason, we investigated why gestational loss occurred in these transgenic mice. Here, we report that placenta detachment and inhibition of angiogenesis occurred in PlGF transgenic mice during the gestational period. Moreover, even when transgenic mice were born, their growth was restricted. CONCLUSIONS: Conclusively, PlGF overexpression prevents angiogenesis by inhibiting Braf, extracellular signal-regulated kinase activation, and downregulation of HIF-1α in the mouse placenta. Furthermore, it affected regulatory T cells, which are important for maintenance of pregnancy.

Turner syndrome revisited: review of new data supports the hypothesis that all viable 45,X cases are cryptic mosaics with a rescue cell line, implying an origin by mitotic loss.

We review the data pertinent to the hypothesis we proposed three decades ago, that all embryos that survive gestation as women with Turner syndrome and have an ostensibly non-mosaic 45,X karyotype, actually are cryptic mosaics for a "rescue line" that includes a viable karyotype. Reanalysis of the prevalence and frequency of 45,X in available data on spontaneous abortuses, and livebirths, confirms prior estimates that 1 % to 1.5 % of all recognizable pregnancies start as an apparent non-mosaic 45,X but about 99 % do not survive gestation. From the rates of 45,X in early embryos, which are notably higher than the inferred rate of gametes hypohaploid for a sex chromosome, as well as the negative maternal age association with 45,X of maternal origin we deduce, in agreement with but on independent grounds from Hall et al. (2006), that a very large proportion of 45,X embryos acquired their 45,X line after fertilization. Results of a search for mosaic cell lines in patients with "Turner syndrome" in several reports indicate that not only does the detection rate of a mosaic line depend upon the number and sensitivity of the markers used, and the number of different tissues examined, but also upon the severity of the phenotype of those cases studied, and the number of cells karyotyped initially. Such factors may explain variation in the extent of detected "cryptic" mosaicism in 45,X individuals (currently at least 50 %). We note a report by Urbach and Benvenitsy (2009) of a gene necessary for placental function, PSF2RA, which lies in the pseudoautosomal-one region of the X and Y chromosomes. Deletion of such a gene could account for the high embryonic lethality in 45,X conceptions, and a rescue line in the placenta could account for embryonic and fetal survival of those cases in which a cryptic mosaic line cannot be found in the usual studies of blood and other tissues from affected individuals. Our primary conclusions are 1) all 45,X individuals with Turner syndrome are cryptic mosaics, 2) absence of the X chromosome in 45,X embryos is caused primarily by mitotic factors, and 3) the placenta is a strong candidate for the location of the rescue line in apparently non-mosaic 45,X individuals.

Comparison of reproductive outcome, including the pattern of loss, between couples with chromosomal abnormalities and those with unexplained repeated miscarriages.

AIM: Chromosomal abnormalities are an important cause of repeated miscarriage. Several studies have discussed the association between chromosomal abnormalities and repeated miscarriage. This study attempts to describe the pattern of miscarriage in this group of women and the eventual pregnancy outcome of couples with chromosomal abnormalities compared with couples with unexplained repeated pregnancy loss. MATERIAL AND METHODS: This was a retrospective study involving 795 couples with repeated miscarriages. RESULTS: Out of 795 couples, 28 (3.52%) were found to have a chromosomal abnormality (carrier group). Over half (65.5%) of the chromosomal abnormalities were balanced reciprocal translocations. After referral, this carrier group had a total of 159 pregnancies, leading to 36 live births (22.6%) among 18 couples. The after referral miscarriage rate in the chromosomal anomaly group (55.6%) was significantly (P < 0.01) higher than that in the unexplained recurrent miscarriage group (28.1%). In couples with chromosomal anomaly, the miscarriages were more likely to occur between 6 and 12 weeks' gestation. CONCLUSIONS: The encouraging cumulative live birth rate of 64.3% for couples with chromosomal anomaly and repeated miscarriage suggests that further attempts at natural conception are a viable option.

Tsc1 deficiency-mediated mTOR hyperactivation in vascular endothelial cells causes angiogenesis defects and embryonic lethality.

This is a study on the role of tuberous sclerosis complex1 (TSC1) mutation and mTOR activation in endothelial cells during angiogenic and embryonic development. Past studies had shown that Tsc1/Tsc2 mutant genes lead to overactivation of mTOR in the regulating pathways in developing fetus. We used conditional Cre-loxp gene knockout approach to delete Tsc1 in mice's endothelial cells in our experimental models. Similarly, activation of mTOR signaling in endothelial cells of these embryos (Tie2-Cre/Tsc1(-/-)) was found. Majority of Tie2-Cre/Tsc1(-/-) embryos died at embryonic day 14.5 in utero. Cardiovascular defects, subcutaneous edema and hemorrhage were present among them. Whole-mount immunostaining in these embryos revealed a disorganized vascular network, defective sprouting of vessels in yolk sac and thickening of the labyrinth layer in the placenta. A thinner ventricular wall with disorganized trabeculae was present in the hearts of Tie2-Cre/Tsc1(-/-) embryos. Endothelial cells in Tsc1-deficient mice showed defective mitochondrial and endoplasmic reticular morphology, but no significant change was observed in cell junctions. The mutant embryos displayed significantly reduced cell proliferation, increased apoptosis and disturbed expression of angiogenic factors. A cohort of mice was treated prenatally with mTOR inhibitor rapamycin. The offspring of these mutant mice survived up to 22 days after birth. It was concluded that physiological TSC1-mTOR signaling in endothelial cells is crucial for vascular development and embryogenesis. We postulated that disruption of normal angiogenic pathways through hyperactive mTOR signaling maybe the mechanism that lead to deranged vascular pathogenesis in the tuberous sclerosis complex.

Absence of cell surface expression of human ACE leads to perinatal death.

Renal tubular dysgenesis (RTD) is a recessive autosomal disease characterized most often by perinatal death. It is due to the inactivation of any of the major genes of the renin-angiotensin system (RAS), one of which is the angiotensin I-converting enzyme (ACE). ACE is present as a tissue-bound enzyme and circulates in plasma after its solubilization. In this report, we present the effect of different ACE mutations associated with RTD on ACE intracellular trafficking, secretion and enzymatic activity. One truncated mutant, R762X, responsible for neonatal death was found to be an enzymatically active, secreted form, not inserted in the plasma membrane. In contrast, another mutant, R1180P, was compatible with life after transient neonatal renal insufficiency. This mutant was located at the plasma membrane and rapidly secreted. These results highlight the importance of tissue-bound ACE versus circulating ACE and show that the total absence of cell surface expression of ACE is incompatible with life. In addition, two missense mutants (W594R and R828H) and two truncated mutants (Q1136X and G1145AX) were also studied. These mutants were neither inserted in the plasma membrane nor secreted. Finally, the structural implications of these ACE mutations were examined by molecular modelling, which suggested some important structural alterations such as disruption of intra-molecular non-covalent interactions (e.g. salt bridges).

The genetic autopsy.

PURPOSE OF REVIEW: To assess the relevance of perinatal and pediatric autopsies in genetic and metabolic diseases. RECENT FINDINGS: Genetic investigations are an important component of fetal autopsies. Despite the advances in imaging diagnosis, the autopsy can identify abnormalities not seen on ultrasound or MRI, as confirmed in recent comparative studies. This is crucial in the diagnosis of syndromic conditions in which the information may be essential to determine the syndrome. Genetic tests may also have a role in the investigation of intrauterine growth restriction and unexplained stillbirth. New techniques have increased the diagnostic yield, even in cases of macerated fetuses.The genetic autopsy is not limited to fetal loss. Genetic abnormalities underlie many cases presenting as sudden unexpected death in infancy, childhood and adolescence, and the need to obtain appropriate samples for genetic analysis applies not only to fetal autopsies. SUMMARY: Fetal autopsies are still the gold standard in diagnosis of fetal abnormalities. Genetic studies are an important component, not only in cases of congenital malformations, but also in unexplained intrauterine death and sudden unexpected death in infancy, as well as in children and adults.

Perinatal pathologic examination of nonintact, second-trimester fetal demise specimens: the value of standardization.

CONTEXT: Management of second-trimester intrauterine fetal demise via dilation and evacuation results in nonintact specimens for pathologic examination. Surgical pathology examination is often mandated; however, evidence on expected findings and specimen evaluation guidelines are lacking. OBJECTIVES: To assess pathologic findings of nonintact, second-trimester fetal demise specimens, through comparison of anatomic abnormalities identified on standardized perinatal examination to individualized general pathology examinations. DESIGN: Single institution, retrospective chart review of 14- to 24-week gestational size fetal demise cases was conducted from May 2006 to October 2010. Suspected abnormalities, chromosomal and pathologic diagnoses were collected. A general surgical pathology examination occurred between May 2006 and October 2008, while a perinatal pathologist examined specimens between October 2008 and October 2010. Statistical analysis consisted of t tests and χ(2) tests by Stata/SE 12.1. RESULTS: One hundred eighteen specimens were included and mean gestational size was 16.0 weeks (standard deviation, 1.6 weeks). Perinatal pathologic evaluation diagnosed significantly more abnormalities than did general pathologic examination (77.3% [34 of 44] versus 9.5% [7 of 75], P < .001). Forty-eight abnormalities were identified: 77.0% (n = 37) were placental and 23.0% (n = 11) were fetal. Chromosomal analysis was done on 73.7% (n = 87 of 118) with 12.6% (n = 11 of 87) showing abnormalities. Among aneuploid specimens, the perinatal pathologist confirmed abnormalities in 66.7% (n = 4 of 6) of cases while general pathologists confirmed abnormalities in 0% (n = 0 of 5) (P = .02). CONCLUSIONS: Systematic surgical pathology examination of nonintact, second-trimester fetal demise specimens yields increased information on fetal or placental abnormalities, which may be clinically useful. Institutions with high-risk obstetrical practices and dilation and evacuation providers should consider integrating a standardized perinatal checklist into educational and practice guidelines.

Long QT syndrome-associated mutations in intrauterine fetal death.

IMPORTANCE: Intrauterine fetal death or stillbirth occurs in approximately 1 out of every 160 pregnancies and accounts for 50% of all perinatal deaths. Postmortem evaluation fails to elucidate an underlying cause in many cases. Long QT syndrome (LQTS) may contribute to this problem. OBJECTIVE: To determine the spectrum and prevalence of mutations in the 3 most common LQTS susceptible genes (KCNQ1, KCNH2, and SCN5A) for a cohort of unexplained cases. DESIGN, SETTING, AND PATIENTS: In this case series, retrospective postmortem genetic testing was conducted on a convenience sample of 91 unexplained intrauterine fetal deaths (mean [SD] estimated gestational age at fetal death, 26.3 [8.7] weeks) that were collected from 2006-2012 by the Mayo Clinic, Rochester, Minnesota, or the Fondazione IRCCS Policlinico San Matteo, Pavia, Italy. More than 1300 ostensibly healthy individuals served as controls. In addition, publicly available exome databases were assessed for the general population frequency of identified genetic variants. MAIN OUTCOMES AND MEASURES: Comprehensive mutational analyses of KCNQ1 (KV7.1, LQTS type 1), KCNH2 (HERG/KV11.1, LQTS type 2), and SCN5A (NaV1.5, LQTS type 3) were performed using denaturing high-performance liquid chromatography and direct DNA sequencing on genomic DNA extracted from decedent tissue. Functional analyses of novel mutations were performed using heterologous expression and patch-clamp recording. RESULTS: The 3 putative LQTS susceptibility missense mutations (KCNQ1, p.A283T; KCNQ1, p.R397W; and KCNH2 [1b], p.R25W), with a heterozygous frequency of less than 0.05% in more than 10 000 publicly available exomes and absent in more than 1000 ethnically similar control patients, were discovered in 3 intrauterine fetal deaths (3.3% [95% CI, 0.68%-9.3%]). Both KV7.1-A283T (16-week male) and KV7.1-R397W (16-week female) mutations were associated with marked KV7.1 loss-of-function consistent with in utero LQTS type 1, whereas the HERG1b-R25W mutation (33.2-week male) exhibited a loss of function consistent with in utero LQTS type 2. In addition, 5 intrauterine fetal deaths hosted SCN5A rare nonsynonymous genetic variants (p.T220I, p.R1193Q, involving 2 cases, and p.P2006A, involving 2 cases) that conferred in vitro electrophysiological characteristics consistent with potentially proarrhythmic phenotypes. CONCLUSIONS AND RELEVANCE: In this molecular genetic evaluation of 91 cases of intrauterine fetal death, missense mutations associated with LQTS susceptibility were discovered in 3 cases (3.3%) and overall, genetic variants leading to dysfunctional LQTS-associated ion channels in vitro were discovered in 8 cases (8.8%). These preliminary findings may provide insights into mechanisms of some cases of stillbirth.

Erythropoiesis in the absence of adult hemoglobin.

During erythropoiesis, hemoglobin (Hb) synthesis increases from early progenitors to mature enucleated erythrocytes. Although Hb is one of the most extensively studied proteins, the role of Hb in erythroid lineage commitment, differentiation, and maturation remains unclear. In this study, we generate mouse embryos and embryonic stem (ES) cells with all of the adult α and ß globin genes deleted (Hb Null). While Hb Null embryos die in midgestation, adult globin genes are not required for primitive or definitive erythroid lineage commitment. In vitro differentiation of Hb Null ES cells generates viable definitive proerythroblasts that undergo apoptosis upon terminal differentiation. Surprisingly, all stages of Hb Null-derived definitive erythroblasts develop normally in vivo in chimeric mice, and Hb Null erythroid cells undergo enucleation to form reticulocytes. Free heme toxicity is not observed in Hb Null-derived erythroblasts. Transplantation of Hb Null-derived bone marrow cells provides short-term radioprotection of lethally irradiated recipients, whose progressive anemia results in an erythroid hyperplasia composed entirely of Hb Null-derived erythroblasts. This novel experimental model system enables the role played by Hb in erythroid cell enucleation, cytoskeleton maturation, and heme and iron regulation to be studied.

Excess female siblings and male fetal loss in families with systemic lupus erythematosus.

OBJECTIVE: Systemic lupus erythematosus (SLE) occurs more frequently among women than men. We aimed to determine whether the male-female ratio in SLE families is different from what would be expected by chance, and whether excess male fetal loss is found. METHODS: All patients with SLE met the revised American College of Rheumatology classification criteria, while unaffected subjects were shown not to satisfy these same criteria. Putative family relationships were confirmed by genetic testing. Pregnancy history was obtained from all subjects, including unrelated control women. Adjusted Wald binomial confidence intervals were calculated for ratio of boys to girls in families and compared to the expected ratio of 1.06. RESULTS: There were 2579 subjects with SLE, with 6056 siblings. Considering all subjects, we found 3201 boys and 5434 girls (ratio 0.59, of 95% CI 0.576-0.602). Considering only the SLE-unaffected siblings, there were 2919 boys and 3137 girls (ratio 0.93, 95% CI 0.92-0.94). In both cases, the ratio of males to females was statistically different from the known birth rate. Among patients with SLE as well as among their sisters and mothers, there was an excess of male fetal loss compared to the controls. CONCLUSION: Siblings of patients with SLE are more likely than expected to be girls. This finding may be in part explained by excess male fetal loss, which is found among patients with SLE and their first-degree relatives.

Natural history of fetal trisomy 18 after prenatal diagnosis.

OBJECTIVE: To evaluate the natural fetal and neonatal outcome for pregnancies with an established prenatal diagnosis of fetal trisomy 18, and a parental decision for continuation of the pregnancy. METHODS: The obstetric and neonatal outcome data for 23 such pregnancies, diagnosed at a single referral Fetal Medicine Centre, were retrospectively obtained. RESULTS: The overall intrauterine fetal death rate was 61%, with a progressive decline in live fetuses up to 39 weeks gestation. For fetuses diagnosed before 20 weeks gestation, there was a trend towards a higher intrauterine fetal death rate (88%), in comparison to those diagnosed after this period (44%) (p=0.06). For live births, the preterm delivery rate was 44%. All infants born alive died within 48 h of birth. CONCLUSION: These data provide reliable information for parental counselling pertaining to risk of intrauterine death when trisomy 18 is diagnosed prenatally. These findings suggest that long-term survival implications for trisomy 18 are different when it is diagnosed prenatally.

The αIIb p.Leu841Met (Cab3(a+) ) polymorphism results in a new human platelet alloantigen involved in neonatal alloimmune thrombocytopenia.

BACKGROUND: Fetal-neonatal alloimmune thrombocytopenia (FNAIT) diagnosis relies on maternofetal incompatibility and alloantibody identification. Genotyping for rare platelet (PLT) polymorphisms allowed the identification of three families with suspected or confirmed maternofetal incompatibility for the αIIb-c.2614C>A mutation (Halle et al., Transfusion 2008;48:14-15). STUDY DESIGN AND METHODS: A polymerase chain reaction-sequence-specific primers amplification assay was designed to genotype the αIIb-c.2614C>A mutation. HEK293 cells expressing αIIb-Leu841 or αIIb-Met841 αIIbß3 forms were used to probe the reactivity of maternal sera from these families and to study the effects of the substitution on αIIbß3 expression and functions. RESULTS: Tested by flow cytometry (FCM), one serum sample specifically reacted with αIIb-Met841 but not with αIIb-Leu841 αIIbß3. This specificity revealed the αIIb-Leu841 polymorphism as a new alloantigen named Cab3(a+) . Cross-match testing using FCM also showed the Cab3(a+) antigen to be expressed at the PLT surface. As for anti-human PLT alloantigen (HPA)-3a (or -3b) and anti-HPA-9bw, detection of anti-Cab3(a+) alloantibodies appeared difficult and required whole PLT assays when classical monoclonal antibody-specific immobilization of PLT antigen test failed. In our FNAIT set, the immune response to Cab3(a+) maternofetal incompatibility could induce severe thrombocytopenias and life-threatening hemorrhages. The p.Leu841Met substitution has limited effects, if any, on local αIIb structure, preserving both αIIbß3 expression and functions. CONCLUSION: The Cab3(a+) polymorphism is a new rare alloantigen (allelic frequency <1%) carried by αIIb that might result in severe life-threatening thrombocytopenias. In Sub-Saharan African populations, higher Cab3(a+) gene frequencies (up to 8.2%; Halle et al., Transfusion 2008;48:14-15) and homozygous people are observed.

ENU mutagenesis identifies the first mouse mutants reproducing human ß-thalassemia at the genomic level.

Forward genetic screens have been performed in many species to identify phenotypes in specific organ systems. We have undertaken a large-scale N-ethyl-N-nitrosourea (ENU) mutagenesis screen to identify dominant mutations that perturb erythropoiesis in mice. Mutant mice that displayed an erythrocyte mean cell volume (MCV) greater than three standard deviations from the population mean were identified. Two of these lines, RBC13 and RBC14, displayed a hypochromic, microcytic anemia, accompanied by a marked reticulocytosis, splenomegaly and diminished red cell survival. Timed pregnancies from heterozygous intercrosses revealed that a quarter of the embryos displayed severe anemia and did not survive beyond embryonic day (E) 18.5, consistent with homozygous ß-thalassemia. Genetic complementation studies with a ß-thalassemia mouse line reproduced the embryonic lethality in compound heterozygotes and a genomic custom capture array and massively parallel sequencing of the ß-globin locus identified the causative mutations. The RBC13 line displayed a nonsense mutation at codon 40 in exon 2 of the ß-major gene, invoking parallels with the common ß(0)39 thalassemia mutation seen in humans. The RBC14 line exhibited a mutation at the polyadenylation signal of the ß-major gene, exactly replicating a human ß-thalassemia mutation. The RBC13 and RBC14 lines are the first ß-thalassemia mouse models that reproduce human ß-thalassemia at the genomic level, and as such highlight the power of ENU mutagenesis screens in generating mouse models of human disease.

Classification of stillbirths and risk factors by cause of death--a case-control study.

OBJECTIVE: To investigate risk factors for stillbirths by cause, using the Causes of Death and Associated Conditions (CODAC) classification system for perinatal deaths. DESIGN: Case-control study. SETTING: Two university hospitals in Oslo, Norway, January 1990 through December 2003. SAMPLE: Women with stillbirth after 22 gestational weeks (n = 377) and controls with live births (n = 1 215), and a subsample of 105 cases and 262 controls. METHODS: Socio-demographic, clinical and thrombophilic risk factors for stillbirths were assessed by cause of death in univariate and multivariable logistic regression analyses. Stillbirths were classified according to CODAC based on information from medical records and validated placenta histology. MAIN OUTCOME MEASURES: Causes of stillbirths in percentages, prevalence, odds ratios and adjusted odds ratios for potential risk factors. RESULTS: Approximately half of the women (n = 190) had placental and 19.4% (n = 73) unknown cause of stillbirth. Placental-associated conditions were registered in 18% (n = 68) of cases with a non-placental or an unknown cause. Smoking and small-for-gestational age were more prevalent in all causal groups, compared with controls, whereas twin pregnancy, hypertension and diabetes were more prevalent only among women with placental and unknown causes of stillbirth. The F2rs179963 polymorphism and combined thrombophilia were significant risk factors for stillbirth with placental causes and antiphospholipid antibodies for stillbirth with non-placental causes. CONCLUSIONS: Two-thirds of all stillbirths (68%) were caused by or associated with placental pathology. Risk factors differed somewhat according to cause, apart from smoking and small-for-gestational age, which were significant risk factors across the causal groups.

Maternal ABCA1 genotype is associated with severity of Smith-Lemli-Opitz syndrome and with viability of patients homozygous for null mutations.

The Smith-Lemli-Opitz syndrome (SLOS [MIM 270400]) is an autosomal recessive malformation syndrome that shows a great variability with regard to severity. SLOS is caused by mutations in the Δ7sterol-reductase gene (DHCR7), which disrupt cholesterol biosynthesis. Phenotypic variability of the disease is already known to be associated with maternal apolipoprotein E (ApoE) genotype. The aim of this study was to detect additional modifiers of the SLOS phenotype. We examined the association of SLOS severity with variants in the genes for ApoC-III, lecithin-cholesterol acyltransferase, cholesteryl-ester transfer protein, ATP-binding cassette transporter A1 (ABCA1), and methylene tetrahydrofolate reductase. Our study group included 59 SLOS patients, their mothers, and 49 of their fathers. In addition, we investigated whether ApoE and ABCA1 genotypes are associated with the viability of severe SLOS cases (n=21) caused by two null mutations in the DHCR7 gene. Maternal ABCA1 genotypes show a highly significant correlation with clinical severity in SLOS patients (P=0.007). The rare maternal p.1587Lys allele in the ABCA1 gene was associated with milder phenotypes. ANOVA analysis demonstrated an association of maternal ABCA1 genotypes with severity scores (logarithmised) of SLOS patients of P=0.004. Maternal ABCA1 explains 15.4% (R²) of severity of SLOS patients. There was no association between maternal ApoE genotype and survival of the SLOS fetus carrying two null mutations. Regarding ABCA1 p.Arg1587Lys in mothers of latter SLOS cases, a significant deviation from Hardy-Weinberg equilibrium (HWE) was observed (P=0.005). ABCA1 is an additional genetic modifier in SLOS. Modifying placental cholesterol transfer pathways may be an approach for prenatal therapy of SLOS.

Paternal deletion of the 11p15.5 centromeric-imprinting control region is associated with alteration of imprinted gene expression and recurrent severe intrauterine growth restriction.

BACKGROUND: Heterogeneous molecular defects affecting the 11p15.5 imprinted gene cluster are associated with the opposite growth disorders Beckwith-Wiedemann Syndrome (BWS) and Silver Russell syndrome (SRS). Maternal deletions of the centromeric domain usually result in BWS, but paternal deletions have been so far associated with normal phenotype. Here we describe a case of recurrent severe Intra-Uterine Growth Restriction (IUGR) with paternal transmission of an 11p15.5 60 kb deletion. METHODS AND RESULTS: Chromosome microarray (CMA), PCR and DNA sequencing analyses showed that two fetuses conceived by a normal couple inherited from their father a 60 kb deletion encompassing the Imprinting Control Region of the 11p15.5 centromeric domain. The two fetuses died in utero with severe growth restriction. PCR amplification of parental DNAs indicated that the father carried the mutation in the mosaic state. DNA methylation and gene expression analyses showed that the deletion led to an imprinting alteration restricted to the centromeric domain and resulting in silencing of KCNQ1OT1 and activation of CDKN1C and PHLDA2. CONCLUSIONS: Our data demonstrate that the phenotype associated with 11p15.5 deletions is strongly influenced by the size of the region involved and indicate imprinting defects leading to CDKN1C and PHLDA2 activation as cause of severe IUGR.

Analysis of several factors of variation of gestation loss in breeding mares.

The files for ultrasound diagnosis of gestating mares belonging to the French equine herd recorded for 3 consecutive years were joined with the files for foal birth of these same mares, allowing the statistical analysis of factors of pregnancy loss. For 28 872 positive diagnoses of gestation, 2898 losses were recorded, that is, a global rate of gestation interruption of 9.12%. The etiology of these interruptions is mainly extrinsic: the year and month of insemination, as well as region for climatic reasons. The intrinsic causes that are implicated are breed of the father (heavy breeds except the hypermetric ones lose fewer pregnancies than warm-blooded breeds), age of the mother (losses are lower in mares of 7 to 10 years of age) and status (mares with foals have fewer pregnancy losses than mares not having foaled the previous year), as well as fetuses with consanguinity (when this increases, the pregnancy losses increase as well). However, the additive genetic effect is extremely low; it corresponds to heritability below 5% and few effects of the environment, common to the offspring of the same mare, were identified. This therefore gives little hope of being able to select against the 'gestation loss' trait.

Monozygotic twins with trisomy 18 of paternal origin: prenatal diagnosis and molecular cytogenetic characterization in a pregnancy with one structurally abnormal living fetus and one intrauterine fetal demise.

OBJECTIVE: To present prenatal diagnosis and molecular cytogenetic characterization of trisomy 18 in a monozygotic twin pregnancy, with one structurally abnormal living fetus and one intrauterine fetal demise. CASE REPORT: A 38-year-old woman was referred for amniocentesis at 16 weeks of gestation because of advanced maternal age. Prenatal ultrasound revealed a monozygotic twin pregnancy, with one structurally abnormal living fetus, and one fetal demise. The body structure details of the dead fetus could not be identified, whereas holoprosencephaly and omphalocele were identified in the living fetus on prenatal ultrasound. Quantitative fluorescent polymerase chain reaction assays using polymorphic DNA markers specific for chromosome 21 and chromosome 18, were applied to the uncultured amniocytes in the amniotic cavity of the living fetus and the cultured amniocytes in the amniotic cavity of the fetus with intrauterine fetal demise. The specimen showed a dosage ratio of 2:1 (paternal:maternal) for chromosome 18-specific markers in both twins. The result was consistent with monozygosity and trisomy 18, and the trisomy 18 was possibly caused by a paternal second meiotic division non-disjunction error or a postzygotic mitotic error. Conventional cytogenetic analysis revealed a karyotype of 47,XY,+18 in both twins. The pregnancy was terminated at 19 weeks of gestation, and a 2g small-for-date macerated twin A and a 166g malformed twin B were delivered. Twin A manifested cebocephaly and omphalocele, and twin B manifested premaxillary agenesis and omphalocele. CONCLUSION: The present case provides evidence that fetal wastage may occur in one of the co-twins in monozygotic twins associated with trisomy 18, and this may in part explain the very rare occurrence of living monozygotic twins with trisomy 18.