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As part of a cytogenetic survey of human spontaneous abortions, the relative frequencies of different categories of chromosome abnormalities were evaluated for possible temporal changes. Three classes of chromosome abnormalities showed significant linear trends; sex-chromosome monosomy and tetraploidy decreased over the study period, while trisomy increased. The increase in trisomy was largely attributable to trisomy 16, which showed a two-fold increase over the duration of the study. The linear increase in trisomy 16 was inversely related to sex-chromosome monosomy. This effect was restricted to women over 30 yr of age and was most pronounced among Oriental women.

Morphological, chemical, and metabolic data indicate that the pathological process occurring in the brains of adults with Down’s syndrome (DS) is very similar to, if not indistinguishable from, that which occurs in the brains of individuals with Alzheimer’s disease (AD). However, discrepancies in the frequency of dementia and possibly in the numbers and distributions of lesions suggest that the pathogenetic mechanisms operative in the two conditions are not necessarily or even likely to be identical. The critical fact that must be kept in mind when considering the effects of trisomy 21 in the causation of DS and of its phenotypic features, including AD, is that the basic problem stems from the presence of an extra but normal chromosome. Several mechanisms have been proposed to explain the relationship of this increased dosage of chromosome 21 genes to the development of AD. These mechanisms include direct injury to the nervous system as the result of increased activity of one or a few genes, as well as indirect effects brought about by abnormalities in the development of the trisomic nervous system or by increased susceptibility to injurious agents. Several model systems for studying these mechanisms have been developed: the trisomy 16 mouse, the trisomy 16***doubt2n mouse chimera, and, most recently, transgenic mice carrying the human CuZn-superoxide dismutase (SOD) gene. In the brains of the transgenic mice, total CuZn-SOD is increased 1.6- to 1.9-fold, but glutathione peroxidase activity and endogenous lipid peroxidation are not increased. It therefore appears that, in a normal environment, an increase in CuZn-SOD activity to the range found in DS does not by itself produce demonstrable alterations in spontaneous lipid peroxidation or in an enzyme system associated with oxygen radical metabolism.

An abnormal female infant, who survived for 10 months with almost complete trisomy 16p and monosomy of sub-band 21q22.3, is described. The chromosome anomaly was the result of an unbalanced segregation of a maternal balanced translocation t(16;21)(p11;q22.3). The partial monosomy was considered to have had little or no adverse phenotypic effect. Cases with trisomy of chromosome 16 material are reviewed. It appears that while full trisomy 16 always results in early spontaneous abortion, trisomy 16p or 16q may be compatible with limited postnatal survival.

We identified an infant male pigtail macaque monkey with a bizarre karyotype which, to the best of our knowledge, has never before been reported in any species. Examination of 107 nuclei from cultured lymphocytes revealed 81 (75.7%) to be trisomic, but with the supernumerary chromosome varying from cell to cell, trisomy 16 being the most common. A small percentage (11.2%) of the nuclei had a normal 42, XY karyotype, and the balance, with the exception of one apparent monosomic (possibly a technical artifact), had multiple chromosome abnormalities. Examination of cultured skin fibroblasts revealed a similar karyotype. We called this karyotype a mosaic variegated trisomy. At birth, the animal had a cleft lip and palate and situs inversus of the heart. He subsequently showed significant developmental delay and apparent mental retardation. There were no clinical symptoms of hematological malignancy, which often have associated acquired chromosome abnormalities such as those described here. The animal survived for 2 yr and 8 mo under intensive care.

A patient who had 3 first-trimester spontaneous abortions (blighted ova) was found to be carrying a balanced 13/14 Robertsonian translocation. In the 2 cases cytogenetically analyzed, different chromosomal aberrations were found (trisomy 16 and supernumerary D elements). Histologic examination of the placentas of all 3 abortions revealed hypovascular or avas-cular villi, hydropic degeneration, and occasional atypical stromal (Hofbaucr-like) cells. In 2 cases the decidua was examined by light microscopy and was diffusely inflamed with a plasmolymphocytic infiltrate. The relation of the maternal translocation to the repeated abortions with chromosome anomalies is discussed.

Many humans with trisomy 21 (Down Syndrome (DS)) have psychomotor and cognitive retardation, congenital heart disease, and hematologic abnormalities. Partial genetic homology exists between mouse chromosome 16 and human chromosome 21; thus, studies of the development of mice with trisomy 16 (Ts16) may provide important insights into the pathogenesis of these defects and into the mechanisms by which they arise in humans. Since Ts16 mice do not survive the late fetal period, chimeras have been formed between Ts16 and normal (2N) mouse embryos to rescue the Ts16 cells for postnatal studies. In this preliminary study of the postnatal development of such chimeras, we examined the proportion of Ts16 cells in a variety of tissues, including the coat, blood, placenta, heart, and brain. The Ts16 cells made significant contributions to almost all tissues examined. Aspects of the behavior and the neurochemistry of adult Ts16 less than-greater than 2N chimeras were found to differ significantly from control (2N less than-greater than 2N) chimeras and from animals of the two donor embryo strains. Ts16 cells comprised a substantial, but not predominant, proportion of cells in each brain region examined. Suggestions for definitive analyses are reviewed.

We have previously proposed that mice trisomic for chromosome 16 will provide an animal model of human trisomy 21 (Down syndrome). However, the value of this model is limited to some extent because trisomy 16 mouse fetuses do not survive as live-born animals. Therefore, in an effort to produce viable mice with cells trisomic for chromosome 16, we have used an aggregation technique to generate trisomy 16 ↔ diploid (Ts 16 ↔ 2n) chimeras. A total of 79 chimeric mice were produced, 11 of which were Ts 16 ↔ 2n chimeras. Seven of these Ts 16 ↔ 2n mice were analyzed as fetuses, just prior to birth, and 4 were analyzed as live-born animals. Unlike nonchimeric Ts 16 mouse fetuses which die shortly before birth with edema, congenital heart disease, and thymic and splenic hypoplasia, all but 1 of the Ts 16 ↔ 2n animals were viable and phenotypically normal. The oldest of the live-born Ts 16 ↔ 2n chimeras was 12 months old at the time of necropsy. Ts 16 cells, identified by coat color, enzyme marker, and/or karyotype analyses, comprised 50–60% of the brain, heart, lung, liver, and kidney in the 7 Ts 16 ↔ 2n chimeric fetuses and 30–40% of these organs in the 4 live-born Ts 16 ↔ 2n animals. Ts 16 cells comprised an average of 40% of the thymus and 80% of the spleen in the Ts 16 ↔ 2n chimeras analyzed as fetuses, with no evidence of thymic or splenic hypoplasia. However, we observed a marked deficiency to Ts 16 cells in the blood, spleen, thymus, and bone marrow of live-born Ts 16 ↔ 2n chimeras as compared to 2n ↔ 2n controls. These results demonstrate that although the Ts 16 ↔ 2n chimeras were, with one exception, viable and phenotypically normal, each animal contained a significant proportion of trisomic cells in a variety of tissues, including the brain. Furthermore, our results suggest that although the abnormal development of Ts 16 thymus and spleen cells observed in Ts 16 fetuses is largely corrected in Ts 16 ↔ 2n fetuses, Ts 16 erythroid and lymphoid cells have a severe proliferative disadvantage as compared to diploid cells in older live-born Ts 16 ↔ 2n chimeras. Ts 16 ↔ 2n chimeric mice will provide a valuable tool for studying the functional consequences of aneuploidy and may provide insight into the mechanisms by which trisomy 21 leads to developmental abnormalities in man.

Recent findings have implicated genes on human chromosome 21 as important in the pathophysiology of Alzheimer's disease (AD). These include the high incidence of the pathological features characteristic of AD in individuals with Down syndrome (trisomy 21) and the localization of both a familial AD gene and the gene encoding amyloid precursor protein on chromosome 21. Substantial genetic homology exists between human chromosome 21 and mouse chromosome 16, including the gene encoding the amyloid precursor protein. Mice that are trisomic for chromosome 16 offer a genetic model for studies relevant to Down syndrome that may also help to clarify molecular mechanisms involved in Alzheimer's disease.

On account of genetic homologies, trisomy 16 in the mouse is generally regarded as a direct animal model of Down's syndrome. Mouse trisomy 19, on the other hand, can be seen as a general model of human trisomies. A detailed evaluation of the cardiovascular system and skeleton in 109 fetuses with trisomy 16 and 422 balanced siblings was carried out in order to systematize the cardiovascular anomalies and the pathogenetic mechanisms responsible for their formation according to (1) general retardation, (2) genetically determined impairment of neural-crest cell migration, and (3) direct gene action on organogenesis. Skeletal malformations in the form of a rib-vertebra syndrome encountered in Ts 16 are described here for the first time. In 108 fetuses and 219 neonates resulting from cross-breeding to induce trisomy 19, we found no significant increase in the frequency of the foregoing anomalies. These results are discussed with regard to a chromosome-specific genetic influence as opposed to a general effect of chromosome imbalance. The specificity of the Ts16 syndrome is compared with that of individual organ anomalies as can be induced by teratogenic agents. Our investigation shows that specific malformation patterns of a particular type can be produced by a variety of methods. However, the overall patterns of the two syndromes are highly chromosome-specific. On detailed examination, the malformation pattern of mouse trisomy 16 shows significant similarities with that of human trisomy 21.

The morphology of placentas from trisomy 16 and trisomy 19 mouse conceptuses aged 12 to 18 gestational days was studied at the light microscopic level. Comparisons were made with placentas from normal littermate animals. Trisomy 16 placentas showed marked changes from normal: 1) the junctional zone showed little indication of normal morphologic differentiation throughout gestation; 2) clusters of germinal trophoblast cells persisted in the labyrinth throughout gestation, whereas these cells disappeared by gestational day 16 in the normal littermate placentas; 3) the labyrinth was reduced in size in the trisomic placentas, and the differentiation of the interhemal membranes was delayed. The size of the labyrinths from trisomy 19 placentas appeared to be decreased, but otherwise the placentas appeared to have normal morphology. These observations and others from the literature show that placental development is affected by the presence of a trisomic genome, and that different trisomies influence the development of the placenta differently. For trisomy 16, we propose that the striking changes of the junctional zone may be associated with the trisomy 16-related gene dosage effect for alpha- and beta-interferon cell surface receptors. Because of the homology for this and other genes on mouse chromosome 16 with genes on human chromosome 21, findings related to the altered development of the trisomy 16 mouse may be relevant to understanding some of the phenotypic variations associated with human trisomy 21, the Down syndrome.

Non-mosaic trisomy 16 was observed in chorionic villus cytotrophoblasts (direct) as well as cultured mesenchymal core cells derived from the pregnancy of a 38-year-old woman. Chromosome preparations from amniotic fluid and neonatal cultures (cord blood) were 46,XX. Normal fetal growth as determined by serial ultrasound examinations occurred throughout the pregnancy, which resulted in a healthy 2724 g female. Multiple biopsies taken from the umbilical cord, placental cotyledons, and fetal membranes were 46,XX. However, a placental nodule and three of six cultures initiated from membranes (amnion and chorion) showed 46,XX/47,XX, + 16 mosaicism. We propose that the trisomy 16 cells arose from residual villi derived from a trisomic cotwin that never developed. This case further demonstrates that normal fetal growth may presage normal outcome irrespective of cytogenetic findings in cytotrophoblasts (direct) and cultured mesenchymal core cells.

Chorionic villi sampling (CVS) was performed on 22 patients who were at risk for a variety of genetic disorders between 8.5-11 weeks of gestation to determine whether the developing fetus had a chromosomal and/or biochemical disorder. A thin Portex catheter was passed transcervically into the chorion frondosum under constant real-time ultrasound guidance, and chorionic villi were obtained by gentle suction. The villi, which have the same genotype as the fetus, were processed directly for chromosomal and/or biochemical analysis. Results were available within six to 24 hours and were confirmed by short term cell cultures within three to ten days. One fetus affected with Tay-Sachs disease and one fetus with trisomy 16 were detected. There were no instances of fetal loss or major complications. In contrast to amniocentesis, the procedure is performed early in pregnancy and results of the genetic testing are available during the first trimester, which allows a first trimester termination of pregnancy if an abnormality is detected and greatly reduces parental anxiety if the findings are normal. We believe that CVS offers an alternative to amniocentesis in the detection of genetic disorders.

A case of trisomy 16q secondary to a paternal 16/18 translocation is described. A comparison of this case with the few other cases of trisomy 16q described in the literature indicates that trisomy for the long arm of chromosome 16 results in a severely affected phenotype and early death. Conversely, patient with trisomy 16p do not have gross abnormalities. We postulate that the prenatal lethality of full trisomy 16 is mainly due to the trisomy for the long arm.

Murine trisomy (Ts) 16 occurs in the fetal and neonatal progeny of males doubly heterozygous for the Robertsonian metacentric chromosomes Rb(16.17)7Bnr/Rb(9.16)9Rma and “all acrocentric” females. The developmental aspects of this trisomy were studied between day 12 of gestation and birth. So far, postnatal survival longer than a few hours after birth has not been observed. The frequency of Ts 16 among all implants decreased from more than 20% on day 14 to values between 4% and 7% shortly before term. Main features of Ts 16 are moderate general hypoplasia, slight developmental retardation, and cardiovascular anomalies. These latter were found in 96% of the trisomies, the great majority belonging to the transposition type, i.e., riding aorta, double outlet right ventricle (DORV) and transposition of the great arteries (TGA). Association with common atrio ventricular (AV)-canal was frequent. Other anomalies as “open eyelid”, hydronephrosis, and hydroureter seem to be attributable to the effects of retardation. Generalized transient edema was frequent in the later gestational stages of Ts 16. Severe cardiovascular malformation is possibly one of the factors responsible for late fetal or neonatal death in some cases. Another factor probably contributing to Ts 16 fetal mortality is insufficiency of placental function due to hypoplasia of the fetal vasculature of this organ. The teratological study of Ts 16 demands interest since evidence has been forwarded to consider this trisomy as an animal model of human trisomy 21.

The trisomy-16 mouse is considered to be a model of human trisomy-21 (Down syndrome). We have examined the electrical membrane properties of cultured dorsal root ganglion (DRG) neurons from normal and trisomy-16 fetuses. Trisomy-16 neurons had significantly accelerated rates of action potential depolarization and repolarization compared to diploid neurons, resulting in decreased spike duration. These changes match those reported in human trisomy-21 DRG neurons. Such abnormalities may contribute to the mental retardation characteristic of Down syndrome.

AFTER the discovery of autosomal trisomies in man, the activity of various enzymes in trisomic cells was measured in the belief that proportionality between gene dose and enzyme activity would help in identifying genes carried by trisomic chromosomes1–5. It became apparent, however, that the trisomic state could produce changes in enzyme activity unrelated to gene dose, probably by interfering with normal physiological processes6. Therefore, verification of the concept that a simple rapport of proportionality between gene dose and concentration of secondary gene product could exist in cells with auiosomal trisomy, as it does in diploid cells with gene mutations or in mouse eggs with different numbers of X chromosomes7, had to await the recent advances in human chromosome mapping. We report here the results of a study of gene dose effects in trisomy 16.

Current and voltage clamp recordings were made with a patch-clamp technique from large, light, dorsal root ganglia (DRG) neurons in tissue culture, derived from trisomy 16 and normal fetal mice. In a Na gradient of [52 mM]o/[28 mM]i, the action potential was accelerated, depolarization and repolarization were faster and the total Na conductance was higher in trisomic neurons. A tetrodotoxin (TTX)-sensitive, fast Na current was demonstrated, about 0.9 nA in trisomic and 0.3 nA in control neurons. The calculated mean specific membrane conductances were 0.74 mS/cm2 and 0.28 mS/cm2, respectively. A TTX-insensitive, slow Na conductance, 3-4 times the fast Na conductance and sensitive to Cd, also was demonstrated, with a 2-fold greater current density and conductance in trisomic as compared with control neurons, of 2.22 +/- 0.54 mS/cm2 and 1.26 +/- 0.09 mS/cm2, respectively. The voltage-dependence and kinetics of the TTX-insensitive, slow, Na current were similar in the two neuronal groups. The results indicate that depolarization during the action potential, in fetal mouse DRG neurons in culture, is mediated by this slow TTX-insensitive Na current. Further, acceleration of depolarization in trisomy 16 neurons is caused by a 2-fold increase in the density of the slow Na current.

Autosomal aneuploidy in mammals adversely affects developmental processes. In human beings, for example, trisomy 21 is the most frequent aneuploidy detected among newborns and the most common known genetic cause of mental retardation. In this review, several hypotheses are discussed that have been proposed to explain the mechanisms by which aneuploidy (especially trisomy) disrupts development. These mechanisms included specific gene dosage effects, generalized disruption of genetic homeostasis, and the influence of the parental origin of the duplicated chromosome. The availability of specific chromosomal rearrangements in mice, coupled with selective breeding schemes, permits generation of aneuploidy of specific chromosomes or chromosomal segments on controlled genetic backgrounds, thus enabling the systematic study of the causes and consequences of defined aneuploidy. Phenotypic characteristics associated with a number of specific aneuploidies in the mouse are discussed. Emphasis is placed on the effects of trisomy 16. Genetic homology between mouse chromosome 16 and human chromosome 21 has led investigators to suggest that analogous mechanisms will be responsible for the developmental abnormalities produced in these respective aneuploidies. Analysis of trisomy 16 mice from the organismal to the subcellular level has revealed a number of phenotypic characteristics (particularly neurobiologic ones) shared with human trisomy 21. The dosage effects of shared genes (or their products) may contribute to the development of these features.

When applied to central nervous system (CNS) cultures taken from normal fetal mice, interferon increases the immunohistochemical expression of the highly phosphorylated 210 kDa neurofilament subunit. This effect can be blocked by the application of an agent which inhibits interferon-mediated metabolic pathways. Murine trisomy 16 is an excellent model for human Down's Syndrome. CNS cultures taken from trisomy 16 fetal mice express greater intensity of 210 kDa neurofilament subunit immunohistochemical staining than do normals. Application of an interferon inhibitor normalizes trisomy 16 CNS neurofilament expression.

Tissue cultures were initiated from 130 spontaneous abortion specimens and 81 were successfully karyotyped. Chromosome abnormalities were found in 50 cases: 12 with XO, 27 with trisomy, 6 with triploidy, 1 with tetraploidy and 4 others. The parental origin was determined in 11 cases of trisomy for an acrocentric chromosome. Two cases were uninformative while 9 non-disjunctions were determined and occurred during meiosis I: 7 were maternal and 2 paternal (both with trisomy 21). Three out of 7 cases with trisomy 16 were informative and resulted from a divisional error during the first meiotic division in the mother. All cases of triploidy were informative. They resulted from non-reduction during meiosis I in the mother (2) or dispermy (4).

An increase in lipid peroxidation has been reported in fetal human trisomy 21 brains. To determine whether this change can be regarded as a consequence of the increase in soluble Cu, Zn-superoxide dismutase (SOD-1) activity caused by the trisomy, we have made use of the trisomy 16 mouse, a model for human trisomy 21. Lipid peroxidation, as malonaldehyde, and the activities of SOD-1 and glutathione peroxidase were studied in diploid and trisomy 16 mouse fetuses and fetal brains and, for comparison, in diploid and trisomy 21 human fibroblasts. SOD-1 activity in diploid mouse brain increased during fetal and postnatal development, but glutathione peroxidase activity was unchanged. Mean SOD-1 activity was almost exactly 50% increased in trisomy 16 fetuses and fetal brains and in human trisomy 21 fibroblasts, confirming the gene dosage effect in both species. The SOD-1 activity in the trisomic fetuses was correlated with that in their matched diploid littermates, suggesting that factors other than the gene dosage also determine activity. Mean glutathione peroxidase activity was not increased in trisomy 16 fetuses or brains and only slightly increased in human trisomy 21 fibroblasts. Mean lipid peroxidation was decreased in fetal trisomy 16 brains but was increased in human trisomy 21 fibroblasts. These results do not lend support to the notion that increased SOD-1 activity is developmentally deleterious and necessarily increases lipid peroxidation and, secondarily, the activity of glutathione peroxidase. The difference between the human and mouse data concerning lipid peroxidation in trisomic brains may be related to structural differences in the lipids which provide the substrate for lipid peroxidation.

In pursuit of attempts at a systematic study of autosomal trisomy in the mouse, an experimental model is presented which permits the induction of specific trisomic conditions. It is based on (1) the occurrence of considerable rates of meiotic anaphase I malsegregation of double metacentric heterozygotes with monobrachial homology, (2) the expectation that trisomics may be found among the unbalanced conditions in the progeny of crosses of the double heterozygotes with “all acrocentric” mice, and (3) the observation that trisomy, in contrast to monosomy or combined monosomy plus trisomy, is the only unbalanced condition surviving beyond day 10. In this design, the specific nature of the trisomy is predetermined by the choice of the double metacentric heterozygote combination and recognized by such criteria as chromosome arm number and the presence of both metacentrics. All trisomic conditions of the mouse so far studied inevitably lead to early or late fetal death. Although the possibility of a systematic survey of all 19 possible autosomal trisomies in the mouse can be anticipated, this report is limited to a study of trisomies (Ts) 1, 8, 11, 12, and 17. Ts 8, 11, and 17 cause severe developmental inhibition at an early stage of development. Death occurs about day 11 or 12. Ts 1 displays a syndrome of moderate to marked developmental retardation and slight to more distinctly disproportionate hypoplasia. These embryos may survive until day 15. In contrast, a lesser extent of hypoplasia and retardation is observed in Ts 12, which, however, almost regularly shows exencephaly and microphtalmia. Obviously, variation of the severity of phenotypic manifestation of the trisomic conditions is due to genie heterogeneity of the animals used in the present study. Current attempts are directed to introduce a sufficient number of metacentrics in a defined background, thus providing the means for future systematic studies of the phenotypic expression of gross genomic imbalance.

From a total of 1312 diagnostic chorionic villus samplings (CVS) there were 22 which showed discordance between the karyotype of the chorionic villi and that of the fetus. This frequency was some 20-fold higher than that reported at amniocentesis. In the majority of discordant cases, the fetal karyotype was normal while the placenta! karyotype was mosaic. In four cases, the placenta! karyotype was non-mosaic (a trisomy 16, a monosomy X, and two tetraploids) while the fetal karyotype was normal. In one case, the placenta was trisomy 18 while the fetus was mosaic. There were two ‘false-negative’ results where short-term methods showed only normal cells while both long-term cultures of chorionic villi and fetal cells were mosaic, in one 46,XY/47.XXY and in the other 46,X Y/47.X Y, + 21.

Alzheimer's disease, which is characterized by amyloid plaques and neurofibrillary tangles, may be attributed to the abnormal expression of gene(s) located on human chromosome 21. Genetic linkage studies have narrowed the region of candidate genes to 21q11.2-21q22 of the long arm of this chromosome. Several single copy sequences within this region, including the amyloid precursor protein (APP), have been mapped to mouse chromosome 16. Reliable strategies exist for breeding Trisomy 16 mice. However, the consequences of developmental overexpression of genes on chromosome 16 have not been previously investigated, because of the lethal effects of this aneuploidy during gestation. In the present report, we employ neural transplantation to study long-term survival and pathogenesis in Trisomy 16 central nervous system tissues. Immunocytochemical staining with antiserum raised against the synthetic APP, beta-A4 and alpha 1-antichymotrypsin revealed numerous densely stained cells within hippocampal grafts of Trisomy 16 mice. Similarly, a population of grafted cells were positively stained following incubation with an antiserum raised against components of the pathological neurofibrillary tangle and with the monoclonal antibodies Tau 6.423 and ubiquitin.

To understand the aetiology and the phenotypic severity of Down syndrome, we searched for transcriptional signatures in a substructure of the brain (cerebellum) during post-natal development in a segmental trisomy 16 model, the Ts1Cje mouse. The goal of this study was to investigate the effects of trisomy on changes in gene expression across development time. The primary gene-dosage effect on triplicated genes (approximately 1.5) was observed at birth [post-natal day 0 (P0)], at P15 and P30. About 5% of the non-triplicated genes were significantly differentially expressed between trisomic and control cerebellum, while 25% of the transcriptome was modified during post-natal development of the cerebellum. Indeed, only 165, 171 and 115 genes were dysregulated in trisomic cerebellum at P0, P15 and P30, respectively. Surprisingly, there were only three genes dysregulated in development and in trisomic animals in a similar or opposite direction. These three genes (Dscr1, Son and Hmg14) were, quite unexpectedly, triplicated in the Ts1Cje model and should be candidate genes for understanding the aetiology of the phenotype observed in the cerebellum.

BACKGROUND: Measurement of nuchal translucency (NT) is a widely used method of screening for chromosomal abnormalities. Increased NT is seen in a diversity of fetal malformations. The mechanism explaining the abnormal fluid accumulation and the transient nature of NT remains unexplained. METHODS: The nuchal regions of normal and trisomy 16 mouse embryos were examined for (lympho)vascular abnormalities using immunohistochemical markers against lymphatic vessels (LYVE-1) and smooth muscle (1A4) and endothelial (CD34) cells. Additionally, an ultrasonographic study was carried out on 17 human fetuses with an increased NT. Two of these fetuses were examined morphologically. RESULTS: In both abnormal human and mouse specimens, we found a mesenchyme lined cavity within the posterior nuchal region as well as bilaterally enlarged jugular LYVE-1 positive lymphatic sacs. The persistence of jugular lymphatic sacs was also confirmed by ultrasound in 14 human fetuses with increased NT. CONCLUSION: Our findings identify the cause of increased NT as mesenchymal oedema in the presence of distended jugular lymphatic sacs, detected by the hyaluronan receptor LYVE-1. The delayed organization and connection of these lymphatic sacs to the venous circulation might explain the transient nature of NT. Disturbance in timing of endothelial differentiation might be a common denominator in the origin of NT, linking cardiovascular and haemodynamic abnormalities.

Somatostatin expression in trisomy 16 mouse neuronal cultures has been studied to investigate the effects of the presence of an extra copy of the pre-pro-somatostatin (ppSS) gene on mouse chromosome 16. The immunoreactivity for somatostatin (SS) was considered in mixed cultures of neurons and glia cells and in neuron-enriched cultures as well as that for neuropeptide Y, glutamic acid decarboxylase, and gamma-enolase immunoreactivity the genes of which are not present on mouse chromosome 16. ppSS and pre-pro-neuropeptide Y (ppNPY) mRNA expression was evaluated and SS immunoreactivity in neurons analyzed by a morphometrical study. The extra copy of the ppSS gene resulted in a significantly increased level of the transcript in trisomic cultures, whereas the expression of the other neuropeptides did not differ. The absence of glial cells in these cultures reduced the number of SS-positive neurons making their number comparable in the trisomic and control cultures. Thus, in spite of higher expression of the ppSS mRNA in trisomic cultures, the determination of this peptidergic phenotype was influenced by the presence of neuroglial cells.

Luteal phase inadequacy was diagnosed and under treatment in a patient with recurrent fetal wastage when a fourth abortion occurred. Karyotypic analysis of the products of conception revealed trisomy 16. Chromosomal abnormalities may explain subsequent abortions in patients with luteal inadequacy.

▼The mouse chromosome 16 (MMU16) contains a large region of conserved sinteny with human chromosome 21 (HSA21). Mice that are trisomic for MMU16 have been used as model for Down syndrome (DS). However, as they do not survive the perinatal period, a new model has been developed, Ts65Dn, which has segmental trisomy 16. This mouse carries an extra chromosome that contains the distal end of MMU16, which is the portion homologous to HSA21 (Ref. 1). A total of 18 loci have been mapped in Ts65Dn with a gene order consistent with their HSA21 counterparts (Ref. 2). The conserved region spans from App to Mx1. Here we report on a rapid and very simple method to type the progeny of Ts65Dn mice based on fluorescence in situ hybridization (FISH) in imprints of several fresh or frozen tissues. The only method to distinguish the Ts65Dn progeny from the non-trisomic counterparts has been, up to now, to perform a karyotype to identify the presence or absence of the marker chromosome (Ref. 3). An alternative way of doing this typing is to perform FISH on metaphases or interphase nuclei using mouse probes from the trisomic region. The main inconveniences of this protocol are that blood has to be drawn from live animals, a culture has to be set up and mice can only be typed after 5–6 weeks of age. We have developed a new protocol based on FISH in interphase nuclei from imprints of a vast number of tissues, even frozen tissues (Figure 1). We have succeeded in typing the Ts65Dn progeny by FISH analysis in imprints of brain, lung, liver, spleen, kidney and tail. Our protocol has also been successfully applied to the typing of mouse

Survival and development in utero involve the intimate interaction of mother, placenta, and embryo or fetus. However, when chromosomal aneuploidy occurs in the placenta and/or embryo or fetus, intrauterine growth retardation and fetal death are frequent outcomes of the pregnancy. Placental insufficiency may play a role in these events. Specifically, insufficiency of the fetal circulation in a hypoplastic placenta may result in underperfusion of the fetus. To examine this, we have studied the development of the placenta in trisomy 16 (Ts16) mice. Ts16 mice were selected because homology has been demonstrated between portions of mouse chromosome 16 and human chromosome 21, specifically that portion of HSA 21 implicated to cause Down Syndrome (DS) when present in triplicate. We examined 5 micron plastic section serial reconstructions of the placentas of Ts16 fetuses and their normal littermates from days 10 through 18 gestation. Morphometrically, the surface area ratio of fetal vasculature to that of the maternal sinuses was much less in the Ts16 fetus than its normal littermate but the ultrastructural characteristics of the placental barrier in the Ts16 fetus and its normal littermate were indistinguishable. The hypoplastic fetal vascular in the placenta could well lead to the underperfusion of the fetus, thus contributing to the aneuploid syndrome.

Murine Trisomy 16 (Ts16) has been proposed as an animal model for Down Syndrome. We examined serial histologic reconstructions of Ts16 fetuses from day 14 through 18 gestation. We found that 94% (N=52) of Ts16 mice had cardiovascular malformations. Endocardial cushion defects were most common (62%) and were associated frequently with conotruncal abnormalities (DORV, 36%; overriding aorta, 35%; PTA, 6%; TGA, 2%) We found thymic hypoplasia in > 90% of Ts16 mice. Consistent with previous observations (Oster-Granite et al., Ped. Res. 17: 300A (1983)), we found facial, basiocciput, and audiovestibular (otic) abnormalities. In reconstructions of the temporal bones, no specimen showed more than 1.5 turns of the cochlea by day 13 (N=2.5). Kirby et al (Science 220: 1059-1061 (1983); Science 223: 498-500 (1984) demonstrated in chick-quail chimeras the cephalic neural crest contribution to thymus development and to aorticopulmonary septation. The combination of cardiac defects, thymic hypoplasia, auditory, and craniofacial malformations we have observed in the Ts16 mouse is consistent with a generalized rhombencephalic neural crest deficiency. This deficiency may be due to failure of cell proliferation or migration, to excessive cell death, or to abnormal cell-cell interactions.

Studies of the neuroanatomic features of murine trisomy 16 (Ts16), an animal model for human trisomy 21 (Ts 21, Down Syndrome), have focussed upon the structural and ultrastructural characteristics of germinative cells within the hippocampal formation. We prepared 5 micron plastic section serial reconstructions of the hippocampal formation of Ts16 and normal littermates from days 12 through 18 gestation.

Mouse fetuses with trisomy 16, an animal model for human trisomy 21 (Down syndrome), have severe defects in several hematopoietic stem cell populations and a marked reduction in thymocyte number. To determine whether there are other defects in the development of the trisomic thymus, the ontogeny of the cell surface antigenic determinants, Thy-1, Ly-1, CD3, CD4, CD8, and TCR v beta, was investigated. The trisomy 16 thymocytes were able to express all of determinants either during fetal life (days 14 to 19 of gestation) or in cultures of intact thymus lobes. However, in all instances (except for Thy-1, which already had a high proportion of expressing thymocytes by day 14), there was a delay in the time at which the determinants were first expressed, as manifested by reduced numbers of positively staining cells. Furthermore, there was also a delay in the rate at which the positively staining cells attained maximal Ag densities. Overall, there was an approximate 2 day lag in development of the fetal trisomic thymocytes. This lag permitted the identification of a large population of CD4-8+ cells prior to the appearance of CD4+8+ thymocytes. These findings are consistent with the identification of CD4-8+ as an intermediate stage between CD4-8- and CD4+8+ in fetal thymocyte ontogeny.