Prenatally detected trisomy 20 mosaicism

BACKGROUND

Trisomy 20 is one of the more common mosaic trisomies detected on amniocentesis and presents with a normal outcome in over 90% of reported cases. Trisomic cells are almost never confirmed in newborn blood and are only rarely found in other fetal or placental samples. Nonetheless, some abnormal outcomes have been reported, including unexplained fetal demise, intrauterine growth restriction, and multiple congenital anomalies. Because of the lack of molecular studies on such cases, it is unknown whether the origin of trisomy or presence of uniparental disomy (UPD) could have some influence on outcome.

METHODS

We present data on six cases of trisomy mosaicism, two detected by chorionic villous sampling (CVS) and four by amniocentesis (AF), submitted to our laboratory for molecular studies.

RESULTS AND CONCLUSIONS

A meiotic origin of the trisomy could be confirmed in only one of these cases. In addition, uniparental disomy was excluded in all four cases for which parents were available for testing. The four cases with low levels of trisomy in amniotic fluid (0%, 10%, 11%, and 12%) were associated with a normal outcome. The remaining two cases of trisomy 20 had high levels of trisomy in amniotic fluid (96% and 58%) and had abnormal outcomes (developmental delay in one and stillbirth with IUGR and severe oligohydramnios in the other). Including previously published cases, there is a clear association with the level of trisomy and outcome, with only 4% abnormal outcomes when <40% trisomic cells were detected. Higher levels of trisomy were also observed in male fetuses as compared to female fetuses (p = 0.01); however, there were no sex differences in frequency of abnormal outcomes.

Effects of triploidy on early human development

OBJECTIVE

The morphologic features of 18 triploid embryos are described.

METHOD

Embryoscopic examination of the embryo in cases of missed abortion before instrumental evacuation from the uterus. Cytogenetic and histologic analysis of the chorionic villi.

RESULTS

Seventeen out of 18 triploid embryos showed structural defects on embryoscopic examination. The most common defects were facial anomalies (n = 15), limb abnormalities (n = 13), microcephaly (n = 11) and neural tube defects (n = 10); 3 embryos were classified as growth disorganized. Placenta of 12 grossly abnormal embryos was diagnosed as partial hydatidiform moles on histological examination.

CONCLUSIONS

The grossly abnormal development of the embryo observed in 12 partial hydatidiform moles indicate that, in aborted triploid embryos, the presence of two paternal genomes might have both placental and embryonic consequences. Transcervical embryoscopy in cases of missed abortion can serve as a central component in additional studies using molecular determination of parental origin of triploidy to establish the true proportion of diandric triploidy among grossly abnormal triploid embryos.

Embryoscopic and cytogenetic analysis of 233 missed abortions: factors involved in the pathogenesis of developmental defects of early failed pregnancies

BACKGROUND

While chromosomal abnormalities are often the cause of missed abortions, other defects could be involved, which might be screened for by transcervical embryoscopy.

METHODS

A total of 272 patients with missed abortion underwent transcervical embryoscopy prior to dilatation and curettage, together with cytogenetic analysis of chorionic villi, using either standard G-banding cytogenetic techniques or comparative genomic hybridization in combination with flow cytometry analysis.

RESULTS

Visualization of the embryo or early fetus (12 cases) was successful in 233 patients, and karyotyping in 221. Among 233 examined cases, 33 had normal external features, 71 were classified as growth-disorganized and 129 had either isolated or multiple defects, including holoprosencephaly, anencephaly, encephalocele, spina bifida, microcephaly, facial dysplasia, limb reduction defect, cleft hand, syndactyly, pseudosyndactly, polydactyly, various forms of cleft lip and an amniotic adhesion. Of the 165 cases with an abnormal karyotype, there were 46 grossly disorganized embryos, 98 multiple defects, six single defects and 15 morphologically normal cases. Of the 56 cases with a normal karyotype, there were 20 grossly disorganized embryos, 16 multiple defects, four single defects and 16 morphologically normal cases.

CONCLUSIONS

A total of 75% of the cases with missed abortion had an abnormal karyotype, 18% had a morphological defect with a normal karyotype, while no embryonic or chromosomal abnormality could be diagnosed in 7% of the cases. Correlation of morphological and cytogenetic findings in spontaneous abortion specimens could provide valuable information for genetic counselling and prenatal care in future pregnancies in couples with a history of repeated pregnancy loss.

Clinical aspects, prenatal diagnosis, and pathogenesis of trisomy 16 mosaicism

INTRODUCTION

Analysis of data from cases of trisomy mosaicism can provide insight for genetic counselling after prenatal diagnosis and for the elucidation of the pathogenesis of trisomy during pregnancy.

METHODS

Statistical analysis was carried out on data from 162 cases of pregnancies with prenatal diagnosis of trisomy 16 mosaicism.

RESULTS

The majority of cases resulted in live birth (66%) with an average gestational age of 35.7 weeks and average birth weight of -1.93 standard deviations from the population mean. Among the live births 45% had at least one malformation, the most common being VSD, ASD, and hypospadias. The level of trisomy on direct CVS (cytotrophoblast) was associated with more severe intrauterine growth restriction (IUGR) and higher risk of malformation, while the level of trisomy on cultured CVS (chorionic villous stroma) was associated only with more severe IUGR. Similarly, the presence of trisomy on amniocentesis (amniotic fluid) was associated with both IUGR and malformation, while the presence of trisomy in the amniotic mesenchyme was associated only with IUGR. Surprisingly, the degree of trisomy in placental tissues appeared to be independent of the degree of trisomy in amniotic fluid and amniotic mesenchyme. The sex of the fetus was not associated with any outcome variables, although there was an excess of females (sex ratio = 0.45) that may be explained by selection against male mosaic trisomy 16 embryos before the time of CVS (approximately 9-12 weeks).

CONCLUSION

The levels of trisomy in different fetal-placental tissues are significant predictors of some measures of outcome in mosaic trisomy 16 pregnancies.

Skewed X-chromosome inactivation is associated with trisomy in women ascertained on the basis of recurrent spontaneous abortion or chromosomally abnormal pregnancies

An increase in extremely skewed X-chromosome inactivation (XCI) (> or = 90%) among women who experienced recurrent spontaneous abortion (RSA) has been previously reported. To further delineate the etiology of this association, we have evaluated XCI status in 207 women who experience RSA. A significant excess of trisomic losses was observed among the women who had RSA with skewed XCI versus those without skewed XCI (P=.02). There was also a significant excess of boys among live births in this group (P=.04), which is contrary to expectations if the cause of skewed XCI was only that these women carried X-linked lethal mutations. To confirm the association between skewed XCI and the risk of trisomy, an independent group of 53 women, ascertained on the basis of a prenatal diagnosis of trisomy mosaicism, were investigated. Only cases for which the trisomy was shown to be of maternal meiotic origin were included. The results show a significantly higher level of extreme skewing (> or = 90%) in women whose pregnancies involved placental trisomy mosaicism (17%) than in either of two separate control populations (n=102 and 99) (P=.02 compared with total control subjects). An additional 11 cases were ascertained on the basis of one or more trisomic-pregnancy losses. When all women in the present study with a trisomic pregnancy (n=103) were considered together, skewed XCI was identified in 18%, as compared with 7% in all controls (n=201) (P=.005). This difference was more pronounced when a cutoff of extreme skewing of 95% was used (10% vs. 1.5% skewed; P=.002). Maternal age was not associated with skewing in either the patient or control populations and therefore cannot account for the association with trisomy. Previous studies have shown that a reduced ovarian reserve is associated with increased risk of trisomic pregnancies. We hypothesize that the association between skewed XCI and trisomic pregnancies is produced by a common mechanism that underlies both and that involves a reduction of the size of the follicular pool.

Transcervical fetoscopic diagnosis of structural defects in four first-trimester monochorionic twin intrauterine deaths

OBJECTIVE

While chromosomal abnormalities are often the cause of early failed pregnancies, other mechanisms could be involved in monochorionic twin intrauterine deaths, that might be screened for careful morphological analysis.

METHODS

Transcervical fetoscopy prior to instrumental evacuation of the uterus was performed in four first-trimester monochorionic twin intrauterine deaths.

RESULTS

We present fetoscopic and cytogenetic findings in four cases of monochorionic twin intrauterine deaths. In the first, generalized abnormal embryonic development observed in both twins was a manifestation of trisomy 20. The second (thoracophagus) and third (acardius) pair of twins had anomalies peculiar to multiple gestations. The fourth pair of twins was remarkable because of the concordance for the observed limb-reduction defects.

CONCLUSION

Malformations of first-trimester monochorionic twin intrauterine deaths might cover a wide spectrum of etiologies from abnormal chromosomes and single gene defects to rare duplication anomalies. Their detection by careful morphological analysis and the identification of a specific mechanism provides valuable information for genetic counseling and prenatal investigation in a future pregnancy.

Evidence for imprinting on chromosome 16: The effect of uniparental disomy on the outcome of mosaic trisomy 16 pregnancies

Although a number of infants with maternal uniparental disomy of chromosome 16 (upd(16)mat) have been reported, the evidence for imprinting on chromosome 16 is not yet conclusive. To test the hypothesis that upd(16)mat has a distinct phenotype, which would support the existence of imprinted gene(s) on chromosome 16, statistical analysis was performed on a large series (n = 83) of mosaic trisomy 16 cases with molecular determination of uniparental disomy status. The incidence of upd(16)mat was 40%, which is consistent with the expected one third from random chromosome loss during trisomy rescue (P = 0.262). In pairwise comparisons, upd(16)mat was found to be associated with fetal growth restriction (P = 0.029) and with increased risk of major malformation (RR = 1.43; P = 0.053). Regression modeling showed that the effect of upd(16)mat on fetal/neonatal weight and malformation is independent of the degree of trisomy detected in the fetus. Regression modeling to control for the degree of trisomy detected in the placenta was not possible due to limited sample size. We conclude that upd(16)mat is associated with more severe growth restriction, and possibly, with higher risk of malformation. Our hypothesis is that imprinted gene(s) exist on chromosome 16 and that abnormal expression of these gene(s) in upd(16)mat cells during development results in decreased cell proliferation. Although we do not advocate prenatal testing for upd(16), studies on the long-term outcome of upd(16)mat neonates is necessary for counseling purposes.

Amnion rupture sequence in a first trimester missed abortion

We report the diagnosis of amnion rupture sequence made by sonography and fetoscopy during the first trimester of gestation in a case of missed abortion. The investigation revealed a demised fetus with the characteristics of 9 weeks of development. The early fetus had an amnion adhesion at the tip of the nose and strands of amnion wrapped around the terminal phalanges of both feet. No defects in addition to the face and limb involvement were identified. The karyotype was normal: 46,XX. In the reported case, fetoscopy allowed confirmation of the sonographic diagnosis of an amnion rupture sequence in the first trimester of gestation and consequently helped to clarify the cause of abortion in this case of early fetal demise.

Comparative genomic hybridization: a new tool for reproductive pathology

OBJECTIVE

To demonstrate the effectiveness of comparative genomic hybridization (CGH) for analysis of reproductive pathology specimens in clinical cytogenetics laboratories.

DESIGN

A total of 856 CGH analyses were performed on various placental and fetal tissues derived from 368 specimens of spontaneous abortions and on placentas from 219 pregnancies with live-born infants. The live-born infants were clinically evaluated as normally developed, with either a normal birth weight or with intrauterine growth restriction; some live-born infants had an abnormal prenatal triple screen with normal cytogenetic results on amniotic fluid cell cultures.

RESULTS

Comparative genomic hybridization analysis was successfully performed on 856 samples from spontaneously aborted specimens and term placentas. Failure of analysis occurred in 1.6% of samples and was due to an insufficient amount of tissue for DNA extraction. Comparative genomic hybridization identified aneuploidy in 53% of spontaneous abortion samples and 3.1% of term placentas.

CONCLUSIONS

Comparative genomic hybridization analysis is a useful clinical tool for detection of aneuploidy in placental and fetal tissues. It provides a genome-wide screen while eliminating tissue culture failures, culture artifacts, and maternal cell contamination. We present practical guidelines for interpreting CGH profiles derived from human reproductive specimens.

Two cases of confined placental mosaicism for chromosome 4, including one with maternal uniparental disomy

Two cases of trisomy 4 mosaicism are reported including one with molecularly confirmed uniparental disomy (UPD) of chromosome 4. Cytogenetic analysis of a chorionic villus sample (CVS) in Case 1 showed complete trisomy 4 in trophoblast and diploidy in chorionic stroma. Amniotic fluid analysis demonstrated a 46,XX complement. After intrauterine fetal death at 30 weeks, molecular analysis confirmed the presence of trisomy 4 of maternal meiotic origin, while fetal tissues showed maternal UPD for chromosome 4. Cultured CVS in Case 2 revealed trisomy 4 in 2/30 cells analyzed. This pregnancy resulted in a healthy livebirth with biparental inheritance of chromosome 4. Molecularly confirmed UPD4 has not been previously reported, and therefore, although the adverse outcome in Case 1 is likely due to the trisomy 4 in the placenta, an imprinting effect associated with UPD4 cannot be excluded.

An association between skewed X-chromosome inactivation and abnormal outcome in mosaic trisomy 16 confined predominantly to the placenta

Skewed X-chromosome inactivation (XCI) is frequently found in the diploid fetal tissues of individuals with mosaic trisomy that originated from a 'trisomic zygote rescue' event. This may result from a high number of trisomic cells in the embryonic cell pool at the time of XCI, which are subsequently eliminated by selection. We hypothesize that extremely skewed XCI in these mosaic cases will be associated with a poor fetal outcome due to failure to completely eliminate the trisomy from all fetal tissues. To test this hypothesis, XCI status was evaluated in 17 cases of prenatally detected trisomy 16 mosaicism. Ten of the 15 informative cases showed extreme XCI skewing ( > or = 90% inactivation of one allele) in blood or other diploid fetal tissues compared to six of the 111 controls (p < 0.001). Among these 10 'skewed' cases, 6 showed an abnormal outcome, defined as developmental abnormalities and/or intrauterine or neonatal death. In contrast, of the 5 cases without extreme skewing, none showed abnormal outcome, although outcome information was incomplete in 1 case. An additional 6 cases analyzed, involving trisomy mosaicism for other chromosomes, showed similar results. Further studies are warranted to determine if XCI status adds useful information to the prediction of pregnancy outcome in prenatally detected mosaic trisomy.

Confined placental mosaicism and genomic imprinting

The concept of confined placental mosaicism and its relationship to genomic imprinting and uniparental disomy is explained in this chapter. Clinically significant imprinting syndromes, such as Prader-Willi syndrome, Angelman syndrome, Beckwith-Wiedemann syndrome, Silver-Russell syndrome and transient neonatal diabetes mellitus, potentially associated with confined placental mosaicism are described and referenced. Non-Mendelian inheritance of recessive mutations in uniparental disomy is illustrated. Both skewed X chromosome inactivation and isolated gonadal mosaicism are outlined as newly recognized consequences of post-zygotic chromosomal mutation and confined placental mosaicism. Clinical management of pregnancies with confined placental mosaicism is proposed as well as future research directions in the field of confined placental mosaicism and its consequences.

Comparative genomic hybridization: a new approach to screening for intrauterine complete or mosaic aneuploidy

In the practice of clinical genetics chromosomal aneuploidy in both mosaic and nonmosaic forms has long been recognized as a cause of abnormal prenatal and postnatal development. Traditionally, cytogenetic analysis of cultured lymphocytes has been used as a standard test for detection of constitutional aneuploidies. As lymphocytes represent only one lineage, chromosomal mosaicism expressed in other tissues often remains undetected. The purpose of this study was to assess the utilization of molecular cytogenetic analysis for detection of chromosomal aneuploidy in placental tissues. Using placentas from 100 pregnancies with viable nonmalformed livebirths, both trophoblast and chorionic stroma were analyzed using comparative genomic hybridization (CGH). In all cases with an indication of chromosomal imbalance by CGH, fluorescence in situ hybridization (FISH) analysis was performed to confirm the presence of aneuploidy. To differentiate between constitutional aneuploidy and confined placental mosaicism (CPM), amniotic membrane was analyzed by CGH and FISH techniques. Our results demonstrated five placentas with CPM for chromosomes 2, 4, 12, 13, and 18, respectively, and two constitutional nonmosaic aneuploidies (47,XXX and 47,XXY). Molecular cytogenetic studies of human placental tissues enables easy analysis of both embryonic (amnion) and extraembryonic (chorion) cell lineages. Detection at birth of chromosomal defects affecting intrauterine placental and fetal development is important because these chromosomal defects may continue to have an influence on postnatal development.

Comparative genomic hybridization in combination with flow cytometry improves results of cytogenetic analysis of spontaneous abortions

More than 50% of spontaneous abortions (SAs) have abnormal chromosomes; the most common abnormalities are trisomy, sex chromosome monosomy, and polyploidy. Conventional cytogenetic analysis of SAs depends on tissue culturing and is associated with a significant tissue culture failure rate and contamination by maternally derived cells. Comparative genomic hybridization (CGH), in combination with flow cytometry (FCM), can detect numerical and unbalanced structural chromosomal abnormalities associated with SAs while avoiding the technical problems associated with tissue culture. Routine cytogenetic and CGH analysis was performed independently on tissue from 301 SAs. Samples shown to be chromosomally balanced by CGH were analyzed by FCM to determine ploidy. Of 253 samples successfully analyzed by both approaches, there was an absolute correlation of results in 235 (92.8%). Of the 18 cases with discrepancies between cytogenetic and CGH/FCM results, an explanation could be found in 17. Twelve samples produced a 46,XX karyotype by cytogenetics, whereas CGH/FCM demonstrated aneuploidy/polyploidy or a male genome, indicating maternal contamination of the tissue cultures. In two cases, where tetraploidy was demonstrated by cytogenetics and diploidy by FCM, tissue culture artifact is implied. In three cases, CGH demonstrated an aneuploidy, and cytogenetics demonstrated hypertriploidy. In one unexplainable case, aneuploidy demonstrated by CGH could not be detected by repeat CGH analysis, conventional cytogenetic, or FISH analysis. These results demonstrate that CGH supplemented with FCM can readily identify chromosomal abnormalities associated with SAs and, by avoiding maternal contamination and tissue culture artifacts, can do so with a lower failure rate and more accuracy than conventional cytogenetic analysis.

Pathogenesis of chromosomal mosaicism and its effect on early human development

Constitutional chromosomal mosaicism is the result of postfertilization mitotic error, the mechanism of which is not fully understood. The distribution of mosaicism in the conceptus depends on the timing, cell lineage(s) involved, cell viability, and chromosome involved. The developmental consequences of mosaicism also are related to its meiotic or somatic type. Meiotic mosaicism often is associated with a more severely adverse effect on the conceptus (see trisomy zygote rescue) due to the presence of uniparental disomy in the embryo/fetus and/or to dysfunction of a trisomic placenta. As mosaicism can be tissue specific, the result of a normal karyotype in cultured lymphocytes does not exclude the presence of mosaicism elsewhere in the conceptus. Mosaicism can best be detected by a combination of traditional cytogenetic analysis with molecular cytogenetic techniques such as comparative genomic hybridization and fluorescence in situ hybridization.

Chromosome abnormalities of eighty-one pediatric germ cell tumors: sex-, age-, site-, and histopathology-related differences--a Children's Cancer Group study

The chromosomes of 81 pediatric germ cell tumors (GCTs) were analyzed as part of two clinical treatment trials, INT-0098 and INT-0097, conducted by the Children's Cancer Group. The analysis of chromosome results showed differences with respect to sex, age, tumor location, and histology. Sixteen of 17 benign teratomas of infants and children less than 4 years old and from gonadal and extragonadal locations were chromosomally normal. Twenty-three malignant GCTs from gonadal and extragonadal locations of the same age group were endodermal sinus tumors and varied in their karyotypic findings. The most common abnormalities were gains of 1q and chromosome 3. Of eight benign ovarian teratomas from older girls, five with normal G-banded karyotypes were determined to be homozygous for Q-band heteromorphisms, suggesting a meiosis II error. Among the 12 malignant ovarian GCTs from older girls, the common abnormalities were loss of 1p/gain of 1q, +3, +8, +14, and +21. Four of eight extragonadal tumors from older boys demonstrated +21; one had +X. Five of the eight had associated constitutional chromosome abnormalities, including one trisomy 21 and three with Klinefelter syndrome. The testicular GCTs of adolescents had abnormalities resembling those found in adult testicular GCT, including near-triploidy, loss of chromosomes 11, 13, and 18, and gain of chromosomes 7, 8, the X chromosome, and an isochromosome 12p. The gain of an isochromosome 12p was only frequent in the tumors from adolescent boys. Deletion of 1p/gain of 1q and +3 were the most common abnormalities among the malignant tumors from both sexes.

Screening of human placentas for chromosomal mosaicism using comparative genomic hybridization

Detection of confined placental mosaicism (CPM) in term placental tissues is usually accomplished by conventional cytogenetic analysis of cultured chorionic stroma and direct preparations from trophoblast or, more recently, by fluorescence in situ hybridization (FISH) on interphase nuclei. In this study, we describe the use of comparative genomic hybridization (CGH) for detection of chromosomal aneuploidy in term placentas and evaluate the sensitivity of this novel approach for CPM diagnosis in multiple placental samples acquired from five pregnancies prenatally diagnosed with CPM7 and CPM16. Each sample of placental villi was separated enzymatically into trophoblast and chorionic stroma, and the level of aneuploidy (three signals/nuclei) in each tissue was determined by FISH analysis, using centromeric DNA probes specific for chromosome 7 (D7Z1/Z2) or 16 (D16Z2). Aneuploidy levels ranged from 5.2-96.1% in the 11 tissues with CPM7 and 9.8-93% in the 29 tissues with CPM16. Subsequently, CGH analysis of DNA from the trophoblast and chorionic stroma of the same tissue sites detected the trisomic clone in all placental tissues with aneuploidy (16%, as determined by FISH analysis). Our results demonstrate the sensitivity of CGH analysis for detection of chromosomal aneuploidy mosaicism and support our contention that the CGH technique is the most effective cytogenetic method for screening term placentas for the presence of CPM.

Altered smooth muscle development and innervation in the lower genitourinary and gastrointestinal tract of the male human fetus with myelomeningocele

PURPOSE

We determine whether smooth and skeletal muscle or nerve density is altered in the lower genitourinary or gastrointestinal tract of male human fetuses with myelomeningocele at 20 weeks of gestation.

MATERIALS AND METHODS

We serially cross sectioned the lower genitourinary and gastrointestinal tracts in 7 male fetuses (mean age 20 weeks of gestation) with myelomeningocele and 4 age matched controls. Immunohistochemical staining was performed using Masson's trichrome stain and antibodies to smooth and skeletal muscle actin. S-100 protein staining for Schwann cell localization and neurofilament protein was also done. Fluorescein and rhodamine double immunolabeling was used to demonstrate the co-expression of smooth and skeletal muscle.

RESULTS

Peripheral neural innervation of the bladder, prostate and rectum was markedly decreased in myelomeningocele. Masson's trichrome and smooth muscle actin staining also demonstrated that smooth muscle was less well differentiated in myelomeningocele specimens. Scant smooth muscle was present in the myelomeningocele bladder and bladder neck with an excess of collagen in an interfascicular and intrafascicular distribution. Double immunofluorescence staining revealed persistent co-expression of smooth and skeletal muscle actin by myocytes in the myelomeningocele detrusor, while in the control bladder there was only smooth muscle expression. The skeletal muscle component of structures in fetuses with myelomeningocele, including the external sphincter, was similar to that in controls. Prostatic size, ductal morphogenesis and smooth muscle were decreased compared to those in controls.

CONCLUSIONS

A global defect exists in the development of smooth muscle in myelomeningocele in the lower genitourinary and gastrointestinal tracts by 20 weeks of gestation. Peripheral nerve density is decreased in smooth muscle in myelomeningocele, suggesting that an intact nervous system is important for the development of normal smooth muscle. Fetal surgery with coverage of the spinal cord in select cases may prevent progressive environmental injury to the somatic nervous system during the second half of gestation. However, achieving normal autonomic function is unlikely due to the extent of early global organ maldevelopment.

Clinical significance of morphologic and genetic examination of spontaneously aborted embryos

PROBLEM

In families with a history of multiple pregnancy losses, the prognosis of future pregnancies is critically dependent on recognizing an accurate pathogenesis of pregnancy loss.

METHOD OF STUDY

Morphological and genetic evaluation of products of conception provides necessary information for clinicians. Modern molecular cytogenetic techniques such as in situ hybridization and comparative genomic hybridization allow cytogenetic diagnosis even when aborted tissues are nonviable.

RESULTS

Correlation of morphological and cytogenetic findings allows distinction between developmental defects associated with chromosomal syndromes and other pathogenesis such as environmental teratogens, and Mendalian or multifactorial inheritance.

CONCLUSION

Pathologists have the responsibility of ensuring that the answers to questions, such as why the failure occurred or whether there is any increased chance of having an abnormal liveborn infant in a future pregnancy, are obtained and that the information is communicated to the parent's obstetrician, geneticist, and family physician.

Skewed X-chromosome inactivation is common in fetuses or newborns associated with confined placental mosaicism

The inactivation of one X chromosome in females is normally random with regard to which X is inactivated. However, exclusive or almost-exclusive inactivation of one X may be observed in association with some X-autosomal rearrangements, mutations of the XIST gene, certain X-linked diseases, and MZ twinning. In the present study, a methylation difference near a polymorphism in the X-linked androgen-receptor gene was used to investigate the possibility that nonrandom X inactivation is increases in fetuses and newborns that are associated with confined placental mosaicism (CPM) involving an autosomal trisomy. Extreme skewing was observed in 7 (58%) of 12 cases with a meiotic origin of the trisomy, but in none of 10 cases examined with a somatic origin of the trisomy, and in only 1 (4%) of 27 control adult females. In addition, an extremely skewed X-inactivation pattern was observed in 3 of 10 informative cases of female uniparental disomy (UPD) of chromosome 15. This may reflect the fact that a proportion of UPD cases arise by "rescue" of a chromosomally abnormal conceptus and are therefore associated with CPM. A skewed pattern of X inactivation in CPM cases is hypothesized to result from a reduction in the size of the early-embryonic cell pool, because of either poor early growth or subsequent selection against the trisomic cells. Since approximately 2% of pregnancies detected by chorionic villus sampling are associated with CPM, this is likely a significant contributor to both skewed X inactivation observed in the newborn population and the expression of recessive X-linked diseases in females.

Cytogenetic and molecular genetic analysis of a pediatric pleomorphic sarcoma reveals similarities to adult malignant fibrous histiocytoma

Cytogenetic and molecular genetic studies were performed on a pleomorphic sarcoma removed from the left atrium of a 15-year-old girl. Histologic analysis was consistent with a storiform-pleomorphic malignant fibrous histiocytoma (MFH). Although MFH is the most common soft-tissue sarcoma of late adulthood. It is extremely rare in childhood and its existence in the pediatric population remains controversial. Cytogenetic analysis revealed several alterations previously associated with adult MFH, including abnormalities of chromosomal bands 11p11 and 19p13. Moreover, the tumor demonstrated homogeneously staining regions (HSR) and double minute chromosomes (dmin) suggestive of gene amplification. We therefore screened the case for amplification of genes localized to chromosomal bands 12q13-14, including the putative protooncogenes MDM2, CDK4, SAS, CHOP, and CLI, which are frequently amplified and overexpressed in adult MFH. Southern and Northern blot analysis confirmed the coamplification of MDM2, CDK4, SAS, and CHOP. To our knowledge, such coamplification studies of the 12q13-14 amplicon have not been previously detected in pediatric MFH. Our results provide cytogenetic and molecular genetic evidence that pediatric and adult MFH are histogenetically related entities.

Maternal uniparental disomy of chromosome 2 and confined placental mosaicism for trisomy 2 in a fetus with intrauterine growth restriction, hypospadias, and oligohydramnios

We present a case of maternal uniparental heterodisomy for chromosome 2 (UPD 2) detected after trisomy 2 mosaicism was found on placental biopsy. This case presented prenatally with severe intrauterine growth restriction (IUGR) and oligohydramnios. The diploid newborn had hypospadias and features consistent with oligohydramnios sequence. He died shortly after birth of severe pulmonary hypoplasia. The term placenta had high levels of trisomy 2 in both the trophoblast and the stroma. A comparison of this case with others reported in the literature suggests that the IUGR and oligohydramnios are likely related to placental insufficiency due to the high levels of trisomy 2 present in the trophoblast of the term placenta and the presence of UPD 2 in the diploid placental line.

Meiotic origin of trisomy in confined placental mosaicism is correlated with presence of fetal uniparental disomy, high levels of trisomy in trophoblast, and increased risk of fetal intrauterine growth restriction

Molecular studies were performed on 101 cases of confined placental mosaicism (CPM) involving autosomal trisomy. The origin of the trisomic cell line was determined in 54 cases (from 51 pregnancies), 47 of which were also analyzed for the presence of uniparental disomy (UPD) in the disomic cell line. An additional 47 cases were analyzed for parental origin in the disomic cell line only. A somatic (postmeiotic) origin of the trisomy was observed in 22 cases and included the majority of cases with CPM for trisomy 2, 7, 8, 10, and 12. Most cases of CPM involving trisomy 9, 16, and 22 were determined to be meiotic. Fetal maternal UPD was found in 17 of 94 informative CPM cases, involving trisomy 2 (1 case), 7 (1 case), 16 (13 cases), and 22 (2 cases). The placental trisomy was of meiotic origin in all 17 cases associated with fetal UPD (P = .00005). A meiotic origin also correlated with the levels of trisomy in cultured chorionic villi samples (CVS) (P = .0002) and trophoblast (P = .00005). Abnormal pregnancy outcome (usually IUGR) correlated with meiotic origin (P = .0003), the presence of fetal UPD (P = 4 x 10(-7)), and the level of trisomy in trophoblast (P = 3 x 10(-7)) but not with the level of trisomy in CVS or term chorion. The good fit of somatic errors with the expected results could have been observed only if few true meiotic errors were misclassified by these methods as a somatic error. These data indicate that molecular determination of origin is a useful predictor of pregnancy outcome, whereas the level of trisomy observed in cultured CVS is not. In addition, UPD for some chromosomes may affect prenatal, but not postnatal, development, possibly indicating that imprinting effects for these chromosomes are confined to placental tissues.

Rare trisomy mosaicism diagnosed in amniocytes, involving an autosome other than chromosomes 13, 18, 20, and 21: karyotype/phenotype correlations

In order to determine the significance of trisomy mosaicism of an autosome other than chromosomes 13, 18, 20, and 21, 151 such cases diagnosed prenatally through amniocentesis were reviewed. These rare trisomy mosaicism cases include 54 from 17 cytogenetic laboratories, 34 from a previous North American mosaicism survey, and 63 from published reports. All were cases of true mosaicism with information available on pregnancy outcome, and with no evidence of biased ascertainment. There were 11 cases of 46/47, +2; 2 of 46/47, +3; 2 of 46/47, +4; 5 of 46/47, +5; 3 of 46/47, +6; 8 of 46/47, +7; 14 of 46/47, +8; 25 of 46/47, +9; 2 of 46/47, +11; 23 of 46/47, +12; 5 of 46/47, +14; 11 of 46/47, +15; 21 of 46/47, +16; 7 of 46/47, +17; 1 of 46/47, +19; and 11 of 46/47, +22. As to the risk of an abnormal outcome, the data showed a very high risk (> 60 per cent) for 46/47, +2, 46/47, +16, and 46/47, +22; a high risk (40-59 per cent) for 46/47, +5, 46/47, +9, 46/47, +14, and 46/47, +15; a moderately high risk (20-39 per cent) for 46/47, +12; a moderate risk (up to 19 per cent) for 46/47, +7 and 46/47, +7 and 46/47, +8; a low risk for 46/47, +17; and an undetermined risk, due to lack of cases, for the remaining autosomal trisomy mosaics. Most cases were evaluated at birth or at termination, so subtle abnormalities may have escaped detection and developmental retardation was not evaluated at all. Comparison of the phenotypes of prenatally diagnosed abnormal cases and postnatally diagnosed cases with the same diagnosis showed considerable concordance. Since the majority of anomalies noted are prenatally detectable with ultrasound, an ultrasound examination should be performed in all prenatally diagnosed cases. In cytogenetic confirmation studies, the data showed much higher confirmation rates in cases with abnormal outcomes than in cases with normal outcomes [81 per cent vs. 55 per cent for fibroblasts (from skin, fetal tissue, and/or cord); 88 per cent vs. 46 per cent for placental cells; 22 per cent vs. 10 per cent for blood cells]. The confirmation rate reached 85 per cent when both fibroblasts and placental tissues were studied in the same case (with trisomic cells found in one or the other, or both). Therefore, one must emphasize that both fibroblasts and placental tissues should be studied. Except for 46/47, +8 and 46/47, +9, PUBS is of limited value for prenatal diagnosis of rate trisomy mosaicism. DNA studies for UPD are suggested for certain chromosomes with established imprinting effects, such as chromosomes 7, 11, 14, and 15, and perhaps for chromosomes 2 and 16, where imprinting effects are likely.

Investigation of effects of pregnant mare serum gonadotropin (PMSG) on the chromosomal complement of CD-1 mouse embryos

PURPOSE

The objective of this study was to examine the effect of superovulatory doses of gonadotropins on the frequency of chromosomal abnormalities of mouse embryos.

METHODS

Chromosome analysis of 8- to 16-cell stage mouse embryos and zygotes was performed by a cytogenetic method.

RESULTS

There was no significant effect of the pregnant mare serum gonadotropin (PMSG) dose on the level of aneuploidy and structural abnormalities from 8- to 16-cell-stage embryos among superovulated groups. However, a simple dose-response relationship between the PMSG dose and the incidence of polyploidy was observed, with the level of polyploidy rising from 2.9% with 10 i.u. PMSG to 10.5% with 15 i.u. PMSG. In zygote stage, the proportion of polyploid embryos also increased as the dose increased, from 1.9% in 5 i.u. to 6.7% in 15 i.u. PMSG. It was observed that the extra chromosomal set in polyploidy embryos originated by both fertilization of a diploid oocyte and dispermy.

CONCLUSIONS

These results indicate a dose-response relationship between the PMSG dose and the incidence of polyploidy in the CD-1 mouse. Both a disturbance at maturation division and an error at fertilization were the cause of polyploidy.

Trisomy 7 CVS mosaicism: pregnancy outcome, placental and DNA analysis in 14 cases

Prenatal diagnosis by chorionic villus sampling (CVS) documents placental chromosomal mosaicism in approximately 2% of viable pregnancies at 9-12 weeks of gestation and can involve various chromosomes and placental cell lineages. Confined placental mosaicism (CPM) is the result of postzygotic mitotic errors occurring in either diploid or trisomic zygotes. With trisomic zygote rescue, depending on the parental origin of the chromosome which is lost, uniparental disomy (UPD) or biparental disomy (BPD) may arise [Kalousek et al., Am J Hum Genet 52: 8-16, 1993]. In this paper, we present 14 pregnancies which were diagnosed by CVS as mosaic trisomy 7. All follow-up amniocenteses showed a normal diploid karyotype. Using both classical cytogenetics and interphase analysis, studies of term placentae showed variable levels of trisomy 7. DNA analysis was performed in nine cases to determine whether the diploid fetus had BPD 7 or UPD 7. Fetal UPD 7 was present only in one case; in eight other cases biparental inheritance was demonstrated. DNA analysis to establish the origin of trisomy 7 in the placenta was fully informative in six cases. One trisomy resulted from a meiotic error and was associated with fetal UPD 7, while the rest were somatic in origin. It is difficult to compare the effect of CPM for trisomy 7 to other trisomies confined to the placenta, as for most chromosomes there are few available cases. It appears that intrauterine fetal growth is not greatly affected by the presence of a trisomy 7 cell line in the placenta. This finding is in contrast to the serious effect of high levels of trisomy 16 within the placenta on fetal intrauterine growth in a series of well-documented cases of CPM 16 [Kalousek et al. 1993].

Analysis of nine pregnancies with confined placental mosaicism for trisomy 2

Karyotypically normal fetuses with completely trisomic or mosaic placentae may be at increased risk for intrauterine growth restriction (IUGR). Molecular and cytogenetic analyses on nine pregnancies with confined placental mosaicism (CPM) for trisomy 2 were performed at two collaborating centres. Seven cases were identified through prenatal testing of chorionic villi (CVS). Two of these seven cases demonstrated complete trisomy 2 while the remaining five cases showed various levels of trisomy 2 (33 per cent-75 per cent cells). Two cases identified after IUGR was observed in newborn infants demonstrated 65 per cent and 100 per cent trisomy 2 in cultured villi from term placentae. In all nine cases, blood chromosome analysis (n = 4), chromosome analysis of amniotic fluid cultures (n = 4), and cultured amnion (n = 5) were normal, failing to demonstrate any trisomic cells in tissues of fetal origin. Molecular studies on the fetal or newborn tissues using dinucleotide repeat polymorphisms on chromosome 2 revealed normal biparental inheritance of chromosome 2 in all nine cases. The parental origin studies of the extra chromosome 2 in the placenta showed that three cases were maternal in origin, at least two of which were consistent with a maternal meiotic non-disjunction giving rise to the trisomy 2, while in one case a paternal origin of the extra chromosome 2 was established.

Confined placental mosaicism

In most pregnancies the chromosomal complement detected in the fetus is also present in the placenta. The detection of an identical chromosomal complement in both the fetus and its placenta has always been expected as both develop from the same zygote. However, in approximately 2% of viable pregnancies studied by chorionic villus sampling (CVS) at 9 to 11 weeks of gestation, the cytogenetic abnormality, most often trisomy, is confined to the placenta. This phenomenon is known as confined placental mosaicism (CPM). It was first described by Kalousek and Dill in term placentas of infants born with unexplained intrauterine growth restriction (IUGR). Contrary to generalised mosaicism, which is characterised by the presence of two or more karyotypically different cell lines within both the fetus and its placenta, CPM represents tissue specific chromosomal mosaicism affecting the placenta only. The diagnosis of CPM is most commonly made when, after the diagnosis of chromosomal mosaicism in a CVS sample, the second prenatal testing (amniotic fluid culture or fetal blood culture analysis) shows a normal diploid karyotype.

An improved technique for molecular cytogenetic analysis of human preimplantation embryos with fluorescence in situ hybridization

OBJECTIVE

To develop a method for the cytogenetic evaluation of preimplantation embryos using nonradioactive centromeric probes for chromosomes 1, 16 and X.

STUDY DESIGN

The embryos used for this study were either fragmented or polyploid embryos rejected from an in vitro fertilization program. Prior to in situ hybridization, the embryos were treated with 0.5% protease. After application of gradual fixation, conventional hybridization protocol was followed.

RESULTS

Ten of 11 embryos showed hybridization signals suggesting that the success rate of in situ hybridization of human embryos is improved when a modified method of digesting the zona pellucida and gradual fixation with removal of the cytoplasm are used.

CONCLUSION

The method described in this study demonstrates that the zona pellucida is the key to successful in situ hybridization of whole human embryos. When the zona pellucida is removed, penetration by a probe becomes possible.

Distribution of mosaicism in human placentae

Traditional first trimester chorionic villus sampling (CVS) for prenatal diagnosis can be performed by cytogenetic analysis of cytotrophoblast or chorionic villous stroma. Approximately 2% of pregnancies studied by CVS show confined placental mosaicism (CPM) involving either cytotrophoblast, stroma or both. We present the results of a cytogenetic study of nine term placentae from pregnancies with prenatally diagnosed CPM. The aneuploid++ cell lines involved trisomies for chromosomes 7,9,16, and X. The cytotrophoblast and villous stroma from multiple biopsies of these placentae were examined using a combination of interphase and metaphase cytogenetic analysis. CPM was detected in all nine of the term placentae and both tissue-specific and site-specific patterns of mosaicism could be discerned. These results indicate that the analysis of villous stroma and cytotrophoblast from multiple placental biopsies is necessary to improve our understanding of the evolution of CPM during pregnancy and its effect on the fetus.

The early amniocentesis study: a randomized clinical trial of early amniocentesis versus midtrimester amniocentesis

OBJECTIVES

The primary purpose of this pilot study was to determine whether the safety of early amniocentesis (EA; 11 weeks to 12 weeks and 6 days) is similar to midtrimester amniocentesis (MA; 15 weeks to 16 weeks and 6 days). The secondary objectives were to determine the cytogenetic success and accuracy of EA compared with MA.

METHODS

This prospective, randomized clinical trial compared continuous ultrasound-guided EA and MA (22-gauge needle) in patients at a late maternal age (> or = 35 years). The procedures were compared for safety, success and accuracy.

RESULTS

Among the 683 women randomized and followed to pregnancy completion, there was a total of 27/344 (7.8%) and 25/339 (7.4%) fetal losses (spontaneous and induced abortions) in the EA and MA groups, respectively (difference 0.4%; CI -3.6 to 4.4%). The rate of postprocedure spontaneous fetal loss was 2.4% (8/330) in the EA group and 3.3% (10/299) in the MA group (NS). The procedure success rate at the first attempt was 97.6% in the EA group and 99.7% in the MA group. There were no diagnostic errors, and all but 2 EA cultures were successful (both repeated successfully). The perinatal outcome was similar in both groups.

CONCLUSIONS

EA appears to be as safe and accurate as MA. A large multicentered, randomized trial is currently underway to verify these results.

Morphologic, immunologic, and cytogenetic classification of acute myeloid leukemia and myelodysplastic syndrome in childhood: a report from the Childrens Cancer Group

The purposes of this report are to reaffirm concordance difficulties with the acute myeloid leukemia (AML) French-American-British (FAB) classification, to present the frequency of previously delineated AML syndromes in pediatric patients and to describe additional characteristic AML profiles utilizing composite morphologic, cytogenetic and immunophenotypic data. Profiles of 124 children with acute myeloid leukemia (AML) and 13 children with myelodysplastic syndrome entered on the Childrens Cancer Group (CCG) pilot study CCG-2861 were examined. Concordance between institutions and reviewers for FAB designation was 65%. Discordance was found principally between M1 and M2, M2 and M4, and M4 and M5. In 49% of marrow specimens, leukemic blasts expressed at least one T lineage-related antigen; 24% expressed the B lineage-related antigen CD19. CDw14 correlated with FAB M4 or M5 morphology and was the only surface antigen associated with a specific FAB subtype. Normal karyotypes were found for 15% of the 75 children with satisfactory karyotype preparations. Recurring aberrations, found in 76% of children, included t(15;17)(q22;q11), t(8;21)(q22;q22), inv(16)(p13q22), rearrangements of band 11q23, t(6;9) (p23;q34), trisomy 8 and monosomy 7. Results from this pilot study and from the current CCG randomized trial correlating morphology, immunophenotyping and cytogenetics, will help to classify AML into unique subgroups with differing clinical consequences or therapy requirements.

Prenatal and postnatal growth failure associated with maternal heterodisomy for chromosome 7

The association of maternal uniparental disomy for chromosome 7 and postnatal growth failure has been reported in four cases and suggests the presence of genomic imprinting of one or more growth related genes on chromosome 7. However, in the reported cases, the possibility of homozygosity for a recessive mutation could not be excluded as the cause of the growth failure as in all cases isodisomy rather than heterodisomy for chromosome 7 was present. We report a case of prenatal and postnatal growth retardation associated with a prenatal diagnosis of mosaicism for trisomy 7 confined to the placenta. DNA typing of polymorphic markers on chromosome 7 has established that the zygote originated as a trisomy 7 with two maternal and one paternal chromosomes 7 with subsequent loss of the paternal chromosome resulting in a disomic child with maternal heterodisomy for chromosome 7. The growth failure seen in this child with heterodisomy 7 lends strong support to the hypothesis of imprinted gene(s) on chromosome 7.

The chromosome pattern of embryos derived from tripronuclear zygotes studied by cytogenetic analysis and fluorescence in situ hybridization

OBJECTIVE

To detect the chromosomal complement of embryos, which developed from tripronuclear zygote, using nonradioactive centromeric probes.

DESIGN

The chromosome pattern of embryos developing from tripronuclear zygote, studied by fluorescence in situ hybridization, was compared with that of embryos studied by standard cytogenetic methods.

SETTING

These embryos were obtained from superovulated patients undergoing IVF treatment.

RESULTS

We have attempted to examine the chromosomal complement of 72 embryos derived from tripronuclear zygotes using both traditional cytogenetic analysis and fluorescence in situ hybridization. Of these 72 embryos, 22 were analyzed with fluorescence in situ hybridization and 50 were analyzed with traditional cytogenetic analysis. For fluorescence in situ hybridization analysis, probes specific for the centromeric regions of chromosomes 1, 16, and X were used, with results being obtained from 18 embryos. One embryo was haploid (5.6%), five were triploid (27.8%), and one was hexaploid (5.6%). Eleven (61%) embryos were mosaic. Traditional cytogenetic analysis could be performed on 25 of 50 embryos. Five (20%) were haploid, one (4%) was diploid, seven (28%) were triploid, one (4%) were tetraploid, and two were hexaploid. Nine (36%) were mosaic.

CONCLUSION

These findings indicate that not all tripronuclear human zygotes develop into triploid embryos. This study also demonstrates the usefulness of fluorescence in situ hybridization for preimplantation diagnosis and screening for chromosome abnormalities.

Interphase cytogenetic analysis of single cell suspensions prepared from previously formalin-fixed and paraffin-embedded tissues

Fluorescence in situ hybridization (FISH) provides a rapid and accurate method for the detection of chromosomal aneuploidy. We have developed a technique for the use of FISH on single cell suspensions produced from either formalin-fixed or paraffin-embedded tissues. Preparation of such tissues involves sequential rehydration, enzymatic digestion to release single nuclei, and hybridization with a fluorescently labeled chromosome-specific centromeric probe. In a clinical setting formalin-fixed tissue from many tissue types is readily available for additional retrospective study. FISH on formalin-fixed tissues is especially beneficial in follow-up studies of cases involving termination after prenatal diagnosis or patients with a malignant disease where previous routine cytogenetics established the chromosomal aneuploidy. The use of this technique eliminates the biases of cytogenetic analysis due to clonal selection in tissue culture, the low number of cells analyzed, and the restriction to only dividing cell populations. We have demonstrated that this application of interphase cytogenetics to the study of various formalin-fixed tissues is amenable to the detection of chromosomal aneuploidies and has specific advantages over cytogenetic analysis.

Molecular cytogenetic analysis of monosomy 7 in pediatric patients with myelodysplastic syndrome

Monosomy 7 is a non-random cytogenetic abnormality that is frequently associated with myelodysplastic syndromes (MDS). Twenty-four bone marrow samples from five pediatric patients with MDS were analysed using both traditional and interphase cytogenetic analysis. The majority of the metaphases were monosomic for chromosome 7 while interphase cytogenetic analysis consistently detected a disomic cell population in nondividing cell populations. This suggests that the monosomy 7 cells have a distinct proliferative advantage compared to the disomic cell population. The results demonstrate that interphase cytogenetic analysis provides important cytogenetic information about non-dividing cell subpopulations, enhancing our understanding of the cell dynamics of normal and monosomy 7 cells in MDS.

Duplication of 9P and hyperplasia of the choroid plexus: a pathologic, radiologic, and molecular cytogenetics study

Duplication of the short arm of chromosome 9 is a rare constitutional abnormality, and the presence of pathologically confirmed hyperplasia of the choroid plexus in one of two cases, and a choroid plexus papilloma in another, raises the possibility of a relationship between the 9p abnormality and abnormal growth of the choroid plexus. Molecular cytogenetic analysis using fluorescence in situ hybridization was used for detection of chromosome 9-derived material in various formalin-fixed choroid plexus abnormalities. Extra copies of chromosome 9-derived material was found in the hyperplastic choroid plexus and in a choroid plexus carcinoma. These findings suggest that there may be an association between duplication of chromosome 9 material and abnormal development of the choroid plexus.

Chromosome investigation in in vitro fertilization failure

PURPOSE

A chromosomal complement of 227 human oocytes was studied to provide information on the frequency and type of chromosomal abnormalities in oocytes failing in vitro fertilization.

RESULTS

Normal haploid chromosome complement was found in 54.6%; chromosomal abnormalities consisting of diploid sets were identified in 16.7% and aneuploidy was observed in 26%. Premature condensation of sperm chromosomes of the GI-phase was observed in 22.9% oocytes. Male infertility was correlated with an increase in the rate of aneuploidy when compared with tubal infertility. The rate of chromosome abnormalities for the oocytes recovered from women who had no fertilized oocytes was significantly higher compared to those with at least one oocyte fertilized.

CONCLUSION

A high frequency of chromosome abnormalities in unfertilized oocytes suggests that natural selection against chromosome abnormalities may occur even prior to fertilization.