Alterations of the fetal extracellular matrix in the nuchal oedema of Down's syndrome

A Chinese multicenter retrospective study of isolated increased nuchal translucency associated chromosome anomaly and prenatal diagnostic suggestions

Extensive researches involving fetuses with multiple ultrasound anomalies have been conducted over the years, but only few were focused on the isolated increased nuchal translucency (NT). On top of that, these limited number of researches were all designed as single-arm studies and the control group was missing. In this study, we conducted a multicenter, retrospective study using amniotic fluid samples collected from 1197 pregnant women having fetuses with isolated increased NT (INT group) or normal NT values (NNT group). Copy number variation sequencing (CNV-seq) was performed to determine their chromosome status and pathogenic variations were validated using SNP array. Overall, 59 chromosome aneuploidies, 34 pathogenic CNVs and 23 copy number variants of unknown significance (VOUS CNVs) were discovered. the INT group had a significantly higher proportion of aneuploidy (19.44%) and pathogenic CNV (8.33%) than the control group (3.49% and 2.30% respectively), and 88.89% of the pathogenic CNVs were related to heart defects. Additionally, more male fetuses were presented in the INT group (68.51%), but they did not have a higher risk (Relative Risk = 1.03) of carrying pathogenic chromosome variations than female fetuses. Our results demonstrated that fetuses with isolated increased NT had a distinct pattern of chromosome abnormality and majority of detected pathogenic CNVs could be linked to the congenital heart disease. Furthermore, because a considerable proportion of pathogenic CNVs were detected, we strongly recommend to perform a joint test of karyotyping and CNV analysis in prenatal diagnosis for fetuses with isolated increased NT in order to decrease the incident of missed diagnosis.

Minor collagens of the skin with not so minor functions

The structure and function of the skin relies on the complex expression pattern and organisation of extracellular matrix macromolecules, of which collagens are a principal component. The fibrillar collagens, types I and III, constitute over 90% of the collagen content within the skin and are the major determinants of the strength and stiffness of the tissue. However, the minor collagens also play a crucial regulatory role in a variety of processes, including cell anchorage, matrix assembly, and growth factor signalling. In this article, we review the expression patterns, key functions and involvement in disease pathogenesis of the minor collagens found in the skin. While it is clear that the minor collagens are important mediators of normal tissue function, homeostasis and repair, further insight into the molecular level structure and activity of these proteins is required for translation into clinical therapies.

Role of collagen type IV in the pathogenesis of increased prenasal thickness in Down syndrome fetuses: sonographic and immunohistological findings

OBJECTIVE

The present study aims to compare the presence and localization of collagen type IV in the prenasal tissue of fetuses with and without Down syndrome (DS).

METHODS

Products of conception were obtained from mid-gestation uterine evacuations of 14 DS fetuses and 15 unaffected controls. Microdissection of the prenasal area and an analysis of the prenasal tissue specimens were performed by a single pathologist, blinded to the karyotype results. Immunohistological presence and localization of type IV collagen were analyzed in the basement membrane (BM), blood vessels, and stroma of the tissues.

RESULTS

There were no statistically significant differences in the presence and localization of antibodies for collagen IV in the blood vessels and stroma between the two groups. However, the presence and localization of type IV collagen in the BM of the prenasal skin were significantly higher in DS specimens compared to the control group (P=0.023). When combining both groups altogether, a significant correlation was found between the increased prenasal thickness (PT) and the high presence and location of collagen type IV, irrespective of the karyotype results (Spearman's correlation; R=0.459; P=0.012).

CONCLUSION

Using the immunohistochemistry technique, we were able to confirm the overexpression of collagen type IV in the BM of the prenasal area. This may explain the sonographic finding of increased PT seen mainly in DS fetuses.

Relationships between Muscle Architecture of Rectus Femoris and Functional Parameters of Knee Motion in Adults with Down Syndrome

This study was designed to measure in vivo muscle architecture of the rectus femoris in adults with Down syndrome, testing possible relationships with functional parameters of the knee motion. Ten adults with Down syndrome and ten typically developed participated in the study. Pennation angle and thickness of the rectus femoris and subcutaneous layer of the thigh were measured via ultrasound imaging. Knee kinematics and electromyographic activity of the rectus femoris were recorded during free leg dropping. Muscle thickness was reduced and subcutaneous layer was thicker in persons with Down syndrome with respect to typically developed adults, but there were no differences in the pennation angle. The area of the rectus femoris EMG activity during the leg flexion was greater in Down syndrome with respect to typically developed adults. The leg movement velocity was lower in Down people than in controls, but the knee excursion was similar between the groups. Functional parameters correlated with pennation angle in the persons with Down syndrome and with muscle thickness in typically developed persons. The description of muscle architecture and the relationships between morphological and functional parameters may provide insights on the limits and the opportunities to overcome the inherent biomechanical instability in Down syndrome.

Angiogenic Gene Expression in Down Syndrome Fetal Hearts

INTRODUCTION

Forty percent of Down syndrome (DS) fetuses have congenital heart defects (CHD). An abnormal angiogenic environment has been described in euploid fetuses with CHD. However, the underlying pathophysiologic pathway that contributes to CHD in DS remains unknown. The objective was to compare the expression of angiogenic factors and chronic hypoxia genes in heart tissue from DS and euploid fetuses with and without CHD.

METHODS

The gene expression profile was determined by real-time PCR quantification in heart tissue from 33 fetuses with DS, 23 euploid fetuses with CHD and 23 control fetuses.

RESULTS

Angiogenic factors mRNA expression was significantly increased in the DS group compared to the controls (soluble fms-like tyrosine kinase-1, 81%, p = 0.007; vascular endothelial growth factor A, 57%, p = 0.006, and placental growth factor, 32%, p = 0.0227). Significant increases in the transcript level of hypoxia-inducible factor-2α and heme oxygenase 1 were also observed in the DS group compared to the controls. The expression of angiogenic factors was similar in DS fetuses and CHD euploid fetuses with CHD.

CONCLUSION

Abnormal angiogenesis was detected in the hearts of DS fetuses with and without CHD. Our results suggest that DS determines an intrinsically angiogenic impairment that may be present in the fetal heart.

Further insights into diastolic dysfunction in first-trimester trisomy-21 fetuses

OBJECTIVE

To assess fetal cardiac function in first-trimester trisomy-21 fetuses as compared with fetuses with other aneuploidies, euploid fetuses with cardiac defects or isolated increased nuchal translucency (NT) and controls.

METHODS

During a 2.5-year period, NT, ductus venosus (DV) blood flow, diastolic filling time, early filling time, tricuspid flow, tricuspid and mitral valve E/A velocity ratios, left ventricle shortening fraction, left myocardial performance index and fetal heart rate were assessed in fetuses with a crown-rump length between 45 and 84 mm undergoing chorionic villus sampling at our center. Cardiac parameters among study groups were compared with the use of 95% CIs.

RESULTS

The study population comprised 28 fetuses with trisomy 21, 25 with other aneuploidies, 94 euploid fetuses with abnormal findings (27 with cardiac defects, 31 with other structural anomalies and 36 with isolated increased NT) and 271 controls. Trisomy-21 fetuses showed signs of diastolic dysfunction such as increased DV pulsatility index and E/A ratios together with a higher prevalence of tricuspid regurgitation. However, no differences were found in euploid fetuses with cardiac defects or isolated increased NT.

CONCLUSIONS

No signs of cardiac dysfunction were observed in euploid fetuses with increased NT or cardiac defects, while in trisomy-21 fetuses signs of diastolic dysfunction could be potentially attributed to volume overload.

Maternal serum placental growth factor at 11-13 weeks' gestation and fetal cardiac defects

OBJECTIVE

To investigate the relationship between fetal heart defects and maternal serum placental growth factor (PlGF), a marker of placental angiogenesis.

METHODS

Maternal serum PlGF, pregnancy-associated plasma protein-A (PAPP-A) and uterine artery pulsatility index (UtA-PI) at 11-13 weeks' gestation were compared in 68 cases of isolated fetal major heart defects and 340 normal controls. Variables were converted into multiples of the median (MoM) after adjustment for gestational age, maternal age, racial origin, weight, parity and method of conception, and then compared between groups. The cardiac defects included 11 cases of obstruction of the left ventricular outflow tract (LVOT), 25 conotruncal abnormalities and 32 valve defects.

RESULTS

The median PlGF-MoM in the heart defect group was lower than in controls (0.80 (interquartile range (IQR), 0.57-1.08) vs 1.00 (IQR, 0.79-1.32); P < 0.0001). Low PlGF levels were observed in the presence of conotruncal and valve defects but not in the presence of LVOT defects. There was no significant difference between the group with fetal heart defects and controls in PAPP-A-MoM (0.95 (IQR, 0.68-1.28) vs 1.01 (IQR, 0.70-1.39); P = 0.292) or UtA-PI-MoM (1.01 (IQR, 0.84-1.28) vs 0.99 (IQR, 0.80-1.20); P = 0.396).

CONCLUSION

In pregnancies with isolated fetal heart defects there is evidence of impaired placental angiogenesis in the absence of impaired placental perfusion and function.

Male-to-female gender ratio in fetuses with increased nuchal translucency

OBJECTIVE

To describe gender distribution in fetuses with increased nuchal translucency (NT) measurements.

METHODS

All fetuses with mild (2.5-2.9 mm) and moderate (3.0-3.5 mm) NT enlargement at 12.0-12.6 weeks gestation were studied. The Z test for proportions was used to compare the gender distribution of this study group to that of all babies born at Roosevelt Hospital in 2008, and to compare the gender distributions of the subgroups.

RESULTS

5109 patients received screening at 12.0-12.6 weeks gestation. 44 fetuses had mild and 28 had moderate enlargement, with a male-to-female ratio of 3.8:1.0, much higher than the 1.06:1.0 ratio among total births at Roosevelt Hospital in 2008 (p < 0.0001). Male-to-female ratio was 7.8:1.0 in fetuses with mild and 1.8:1.0 with moderate NT enlargement (p = 0.03). Among fetuses with mild NT enlargement, 3 males had aneuploidy; among those with moderate enlargement, 6 fetuses had aneuploidy, 3 males and 3 females. Seven pregnancies with aneuploidy were voluntarily terminated. All pregnancies carried to term were healthy.

CONCLUSIONS

More males than females had mild NT enlargement on first-trimester screening, but unless aneuploidy was detected they had normal birth outcomes. A slightly larger NT may be normal in males, while indicating possible fetal abnormalities in females.

The anatomy of fetal peripheral lymphatic vessels in the head-and-neck region: an immunohistochemical study

Using D2-40 immunohistochemistry, we assessed the distribution of peripheral lymphatic vessels (LVs) in the head-and-neck region of four midterm fetuses without nuchal edema, two of 10 weeks and two of 15 weeks' gestation. We observed abundant LVs in the subcutaneous layer, especially in and along the facial muscles. In the occipital region, only a few LVs were identified perforating the back muscles. The parotid and thyroid glands were surrounded by LVs, but the sublingual and submandibular glands were not. The numbers of submucosal LVs increased from 10 to 15 weeks' gestation in all of the nasal, oral, pharyngeal, and laryngeal cavities, but not in the palate. The laryngeal submucosa had an extremely high density of LVs. In contrast, we found few LVs along bone and cartilage except for those of the mandible as well as along the pharyngotympanic tube, middle ear, tooth germ, and the cranial nerves and ganglia. Some of these results suggested that cerebrospinal fluid outflow to the head LVs commences after 15 weeks' gestation. The subcutaneous LVs of the head appear to grow from the neck side, whereas initial submucosal LVs likely develop in situ because no communication was evident with other sites during early developmental stages. In addition, CD68-positive macrophages did not accompany the developing LVs.

Cardiac function in trisomy 21 fetuses

OBJECTIVES

Trisomy 21 is associated with an increased nuchal translucency thickness (NT), abnormal ductus venosus (DV) flow at 11-14 weeks' gestation and congenital heart defects (CHD), and cardiac dysfunction has been hypothesized as the link between them. We therefore aimed to investigate whether cardiac function is altered in trisomy 21 fetuses.

METHODS

Between December 2003 and June 2009, we performed echocardiography on 46 trisomy 21 fetuses (28 with structurally normal heart and 18 with CHD) and on 191 chromosomally/phenotypically normal fetuses with a confirmed normal heart (87 with normal NT and 104 with NT ≥ 95(th) percentile), between 11 and 35 weeks' gestation. Measurements included: E- and A-wave peak velocity, E/A velocity ratio and E/time velocity integral (TVI) ratio over atrioventricular valves; myocardial performance index (MPI); semilunar valve peak velocity and acceleration time; stroke volume (SV); cardiac output; and DV pulsatility index for veins (PIV) at 11-14 weeks' gestation. Data were categorized into three different age groups for analysis (11 to 13 + 6, 14 to 21 + 6 and 22 to 35 weeks' gestation).

RESULTS

The tricuspid valve (TV) A-wave velocity and aortic valve peak velocity were significantly reduced in trisomy 21 compared with normal fetuses. Other highly significant differences found in trisomy 21 fetuses at 11-14 weeks' were increased TV-E/A ratio and DV-PIV, and decreased pulmonary valve peak velocity. We also observed evidence of left ventricular (LV) systolic dysfunction, reduced SV and increased MPI. After 14 weeks' gestation, the mitral valve A-wave peak velocity and E/TVI ratio were significantly reduced in the trisomy 21 fetuses with normal hearts compared with the controls with increased NT.

CONCLUSIONS

In comparison with controls with normal or increased NT, cardiac function in trisomy 21 fetuses is abnormal irrespective of the presence of CHD. Evidence for cardiac loading (increased preload and afterload) and LV systolic (in the first trimester) and later diastolic dysfunction was observed.

Male gender as a favorable prognostic factor in pregnancies with enlarged nuchal translucency

OBJECTIVE

The aim of this study was to investigate the influence of fetal gender on pregnancy outcome in fetuses with enlarged nuchal translucency (NT).

METHODS

Pregnancy outcomes of all women who underwent an NT measurement at our institution between January 2000 and November 2007 were retrospectively reviewed. Separate analyses were performed for fetuses with normal and with enlarged (>or= 95(th) percentile) NT.

RESULTS

A normal NT was measured in 3637 males (51.4%) and 3435 females (48.6%). Of the fetuses with enlarged NT 365 were males (57.4%) and 271 females (42.6%) (P = 0.001). In this group a normal pregnancy outcome-of those pregnancies for which the outcome was known-was registered for 187/332 (56.3%) of the male fetuses and 98/249 (39.4%) of the female fetuses (P < 0.001; relative risk (RR) for adverse outcome for male gender, 0.72). Eighty percent of the chromosomally normal male fetuses with an enlarged NT had an uneventful pregnancy outcome; this increased to 90% when only the male fetuses with NT measurements >or= 95(th) percentile and < 99(th) percentile and normal karyotype were considered (RR for adverse outcome for male gender, 0.47).

CONCLUSION

In a population of fetuses with enlarged NT there are significantly more males. Male fetuses with enlarged NT and normal chromosomes have an almost two-fold greater chance of a favorable outcome than females. We believe that a minimal degree of NT enlargement in male fetuses without genetic or structural anomalies may be interpreted as a feature of accelerated growth or, alternatively, as a maturational delay of the cardiovascular system more common in males, leading to moderately increased nuchal fluid accumulation.

Faithful tissue-specific expression of the human chromosome 21-linked COL6A1 gene in BAC-transgenic mice

We created transgenic mice with a bacterial artificial chromosome (BAC) containing the human COL6A1 gene. In high-copy and low-copy transgenic lines, we found correct temporal and spatial expression of COL6A1 mRNA, paralleling the expression of the murine Col6a1 gene in a panel of nine adult and four fetal organs. The only exception was the fetal lung, in which the transgene was expressed poorly compared with the endogenous gene. Expression of COL6A1 mRNA from the transgene was copy number-dependent, and the increased gene dosage correlated with increased production of collagen VI alpha 1 in skin and heart, as indicated by Western blotting and immunohistochemistry. COL6A1 maps to Chromosome 21 and this gene has been a candidate for contributing to cardiac defects and skin abnormalities in Down syndrome. The low-copy and high-copy COL6A1 transgenics were born and survived in normal Mendelian proportions, without cardiac malformations or altered skin histology. These data indicate that the major promoter and enhancer sequences regulating COL6A1 expression are present in this 167-kb BAC clone. The lack of a strong cardiac or skin phenotype in the COL6A1 BAC-transgenic mice suggests that the increased expression of this gene does not, by itself, account for these phenotypes in Down syndrome.

Quantitative evaluation of collagen type VI and SOD gene expression in the nuchal skin of human fetuses with trisomy 21

OBJECTIVE

To investigate the involvement of the genes encoding for COL6A1, COLA2 and super-oxide dismutase (SOD) in the mechanism for the retention of subcutaneous fluid in fetuses with trisomy 21.

METHODS

During a 7-month period (November 2004-May 2005), human fetal skin from the nuchal region was obtained from euploid fetuses and from fetuses with trisomy 21 following abortions and terminations of pregnancy. Cell cultures were performed from nuchal skin. Quantification of COL6A1, COL6A2, COL6A3 and SOD mRNAs were performed using real-time quantitative RT-PCR.

RESULTS

Twelve fetuses were studied between 13-15 and 19-20 weeks of gestation including 7 cases of trisomy 21. A significant overexpression of genes of interest was demonstrated in trisomy 21 fetuses when compared with euploid fetuses, in the first and in the second trimester of pregnancy (p < 0.0001).

CONCLUSION

This study demonstrates a homogeneous overexpression of the genes encoding for alpha1 and alpha2 chains of Collagen type VI, and SOD in nuchal skin of human trisomy 21 fetuses. Persistence of this overexpression in the second trimester of pregnancy, despite the absence of an enlarged nuchal translucency (NT), may characterize some compensatory mechanisms.

Hyaluronan content of Wharton's jelly in healthy and Down syndrome fetuses

The mechanisms by which the excess genetic material of chromosome 21 results in the dysmorphologic features of Down syndrome (DS) are largely unknown. It has been found that the extracellular matrix of nuchal skin of DS fetuses exhibits an higher content of hyaluronan (HA) compared to that of euploid fetuses. Since HA plays a central role in many morphogenetic processes during embryogenesis, an alteration in its metabolism could be involved in the pathogenesis of several structural defects of DS. The extracellular matrix of umbilical cord (UC) is the mammalian tissue with one of the highest content of HA. Therefore we sought to explore the quantitative HA modifications during gestation, tissue distribution and HA metabolism in euploid and DS UCs. Euploid UCs (n=28) and UCs from DS fetuses (n=13) were obtained after termination of pregnancy, spontaneous abortion, or at delivery. Quantitative and molecular size analysis were performed using HPLC and FPLC. Tissue distribution was visualized by immunohistochemistry. Gene expression for HA synthases (HAS) and hyaluronidases (HYAL) were quantified by real-time PCR techniques and HYAL activity was detected by zymography. In euploid UC only HA of a molecular weight of 1700 kDA was present while in DS UC an additional lower weight HA molecule of 1100 kDA was found. Immunohistochemistry showed a larger amount of Wharton's jelly HA in DS UCs than in euploid UC. Real-time PCR analysis showed that HAS 2 and HYAL 2 were expressed at significant levels in all specimens. A higher expression of HAS 2 and a lower expression of HYAL 2 was found in the Wharton's jelly of DS fetuses compared to that of euploid fetuses at 14 weeks of gestation. On the contrary, at term HYAL 2 expression was higher in DS specimens than in those from euploid fetuses. Zymographic studies showed a similar behavior with a lower HYAL activity at early gestation and a higher HYAL activity at term gestation in DS UCs compared to euploid specimens. Therefore we can conclude that HA is more represented in DS UCs than in euploid UCs. A complex alteration of the HA metabolism characterized by an increased synthesis of lower weight HA molecules is a peculiarity of DS UCs.

Physiopathologie de la nuque épaisse

OBJECTIVES

Increased physiological nuchal translucency (NT) between 10 and 14 weeks of gestation is associated with chromosomal anomalies, mainly trisomy 21, developmental malformations and with normal fetus outcome. The aim of this study is to understand the cellular mechanisms leading to increased NT.

MATERIALS AND METHODS

We examined five nuchal samples, a normal fetus from a fetal loss with a normal NT, a trisomy 21 fetus with an increased NT, two karyotypically normal fetuses with increased NT and a fetus with increased NT associated with an isolated cardiopathy. These morphological data were correlated with data from the literature.

RESULTS

The pathological mechanism of increased NT is a posterior median mesenchymal edema of the fetal neck. It is associated with bilateral distension of jugular lymphatic vessels.

CONCLUSION

Increased NT mechanisms are mainly related to a disturbance of embryonic lymphangiogenesis which might be a common denominator of the alteration of the composition of the extracellular matrix and of the cardiovascular and hemodynamic disorder. Nuchal morphological studies should be systematically performed to understand the mechanisms of increased NT.

Curva de referência para a medida da translucência nucal na população capixaba

OBJETIVO: Estudar o comportamento da medida da translucência nucal (TN) na população capixaba, no período entre a 10ª e a 14ª semanas de gestação. MATERIAIS E MÉTODOS: Estudou-se de forma transversal 853 fetos, consecutivamente, que apresentaram cariótipos ou fenótipos normais. Todos os fetos foram submetidos, durante a ultra-sonografia de rotina, à medida da TN. A análise estatística utilizou o teste "t" de Student e ANOVA. O teste de regressão ajustou o melhor modelo matemático para traduzir o comportamento da TN. RESULTADOS: A idade materna variou de 14 a 49 anos (média de 30,2 anos), sendo que 22,1% encontravam-se com mais de 35 anos. A TN mostrou comportamento crescente com a idade gestacional e o comprimento cabeça-nádegas (CCN). Houve 73 casos (6,46%) de fetos normais com TN maior que 2,5 mm. O melhor modelo matemático encontrado para representar o comportamento da TN foi a regressão linear simples (TN = 0,414 + 0,020 × CCN), que permitiu estabelecer curva de normalidade com os percentis 5, 10, 25, 50, 75, 90 e 95. CONCLUSÃO: A TN apresenta comportamento crescente com o avançar da idade gestacional, no período de 10 a 14 semanas. A população capixaba apresenta medidas de TN semelhantes às demais populações já testadas.

Glycosaminoglycans and proteoglycans in the skin of aneuploid fetuses with increased nuchal translucency

BACKGROUND

First trimester increased fetal nuchal translucency is associated with fetal aneuploidies. One of the mechanisms of pathophysiology could be an abnormal extracellular matrix facilitating the formation of an interstitial edema. A previous study investigating interstitial edema in first trimester fetuses found large amounts of hyaluronan in the skin of fetuses with trisomy 21. The aim of this study was to establish distribution patterns for a number of other glycosaminoglycans-dermatan, heparan and keratan sulphate, chondroitin-6-sulphate and chondroitin-4-sulphate proteoglycan-in the nuchal skin of normal and chromosomally abnormal fetuses at 11-14 weeks. We also investigated whether biglycan (BGN), which is located on chromosome X, is underexpressed in fetuses with Turner syndrome. Decorin (DCN), a similar-sized proteoglycan located on chromosome 12, was taken as a control.

METHODS

We studied the distribution and concentration of various extacellular matrix components using immunohistochemistry, a double staining technique, in-situ hybridization, Northern and Western blot analysis.

RESULTS

Chondroitin-6-sulphate and chondroitin-4-sulphate proteoglycan were increased in Turner syndrome fetuses and BGN seemed to be underexpressed compared with normal controls, while DCN was not. Dermatan, heparan and keratan sulphate showed no significant abnormal distribution in trisomies 21, 18, 13, or in Turner syndrome, compared with normal. Western and immunohistochemical analysis revealed that absence of a second X chromosome, as is the case in Turner syndrome, affects BGN protein pattern.

CONCLUSIONS

An abnormal amount of glycosaminoglycans and proteoglycans presumably contributes to increased nuchal translucency.

Does a ?notched? nuchal translucency indicate Down syndrome fetuses or other adverse pregnancy outcome?

The aim of the present study was to assess the sonographic contour of the increased nuchal translucency (NT) and to correlate this with pregnancy outcome. Fifty sonographic images of fetuses with increased NT [> 95th centile thickness of the normal range for crown-rump length (CRL) between 38 and 84 mm] were retrospectively assessed. In all the cases a complete pregnancy and even infancy follow-up (< 36 months) was available. The NT appearances were subdivided into two forms: a 'notched' or 'uniform' appearance. The images were correlated with karyotype results [trisomy 21 (DS) vs euploid cases] and pregnancy outcome. Complicated outcomes were classified as being either DS fetuses, miscarriage or termination of pregnancy because of structural anomaly. Thus 30/35 (86%) of the euploid fetuses had a 'uniformly' increased NT, whereas 8/13 DS cases (62%) had a 'notched' appearance (Fisher's exact test, p = 0.004). Additionally, 27/29 fetuses (93%) which had an uneventful pregnancy outcome had a 'uniform' increased NT, whereas 12/26 (57%) of the fetuses which had adverse pregnancy outcome had a 'notched' appearance of their NT (Fisher's exact test, p < 0.001). Although it was not possible to correlate the sonographic data with post-evacuation microdissection findings, it is possible that a uniformly shaped, increased NT may be more representative of a developmental delay in a normal fetus. Conversely, a 'notched' nuchal surface may represent abnormal lymphatic or cardiovascular development more commonly seen in DS fetuses.

Pregnancy outcome and infant follow-up of fetuses with abnormally increased first trimester nuchal translucency

The numbers of fetuses with an abnormal increased first trimester nuchal translucency (NT) but a confirmed normal anatomy and karyotyping is relatively small and therefore a challenge for prenatal counselling. The aim of the current study was to assess the long-term pregnancy outcome and infancy prognosis of 78 fetuses with NT > 95th centile of the normal range for crown-rump length (CRL). The most common abnormalities in this group were aneuploidy, which affected 32 of the fetuses followed by four and three cases which were miscarried or had cardiac defects respectively. The remaining euploid fetuses with normal detailed scans were followed throughout their infancy (mean 24 months; range 12-36 months). Post-natally, except for a correctable case of ventricular septal defect and a case of posterior urethral valve, no other abnormalities were detected. After excluding all aneuploid cases and using the maternal age as a second variable, an uncomplicated pregnancy outcome could be anticipated in 17 cases (100%) when the maternal age was <30 years and NT between 95th centile and 5 mm. However, the chance of a normal outcome dropped to 50% in four cases with maternal age > or =30 years and NT > or =5 mm (Fisher's exact test; P: = 0.02). These findings suggest that the long-term prognosis of the euploid fetuses with large NT (<5 mm) is reassuring in younger women.

Germ cell migration and early development of the gonads in the trisomy 16 mouse--an animal model for Down's syndrome

The aneuploid condition of patients with Down's syndrome (trisomy 21) frequently leads to a sub- or infertility of these individuals. Gonads from adults and fetuses with trisomy 21 demonstrated histologically a remarkable reduction in germ cells. Disorders in the germ cell migration, the early development of the gonads as well as meiotic defects are thought to contribute to this pathomorphology. To gain information about premeiotic defects, investigations on the trisomy 16 mouse, an animal model for Down's syndrome, were carried out. By means of morphometric studies a delay in migration and a reduction in primordial germ cells was evaluated in trisomic mice of embryonic day 11 (E11). At day E13 a generalized growth retardation of the developing gonads was obvious in trisomic animals. Additionally performed electron microscopic examinations revealed signs of germ cell demise in trisomy 16 mice. Thus, the mechanisms of a diminished proliferation capacity, impaired migration and premature death of germ cells represent premeiotic disorders that presumably contribute to the pathomorphology observed in the gonads of individuals with Down's syndrome.

The role of the alpha3(VI) chain in collagen VI assembly. Expression of an alpha3(VI) chain lacking N-terminal modules N10-N7 restores collagen VI assembly, secretion, and matrix deposition in an alpha3(VI)-deficient cell line

Collagen VI is a microfibrillar protein found in the extracellular matrix of virtually all connective tissues. Three genetically distinct subunits, the alpha1(VI), alpha2(VI), and alpha3(VI) chains, associate intracellularly to form triple-helical monomers, which then assemble into disulfide-bonded dimers and tetramers before secretion. Although sequence considerations suggest that collagen VI monomers composed of all three chains are the most stable isoform, the precise chain composition of collagen VI remains controversial and alternative assemblies containing only alpha1(VI) and alpha2(VI) chains have also been proposed. To address this question directly and study the role of the alpha3(VI) chain in assembly, we have characterized collagen VI biosynthesis and in vitro matrix formation by a human osteosarcoma cell line (SaOS-2) that is deficient in alpha3(VI) production. Northern analysis showed an abundance of alpha1(VI) and alpha2(VI) mRNAs, but no detectable alpha3(VI) mRNA was apparent in SaOS-2 cells. By day 30 of culture, however, small amounts of alpha3(VI) mRNA were detected, although the level of expression was still much less than alpha1(VI) and alpha2(VI). Collagen VI protein was not detected in SaOS-2 medium or cell layer samples until day 30 of culture, demonstrating that despite the abundant synthesis of alpha1(VI) and alpha2(VI), no stable collagen VI protein was produced without expression of alpha3(VI). The alpha1(VI) and alpha2(VI) chains produced in the absence of alpha3(VI) were non-helical and were largely retained intracellularly and degraded. The critical role of the alpha3(VI) chain in collagen VI assembly was directly demonstrated after stable transfection of SaOS-2 cells with an alpha3(VI) cDNA expression construct that lacked 4 of the 10 N-terminal type A subdomains. The transfected alpha3(VI) N6-C5 chains associated with endogenous alpha1(VI) and alpha2(VI) and formed collagen VI dimers and tetramers, which were secreted and deposited into an extensive network in the extracellular matrix. These data demonstrated that alpha3(VI) is essential for the formation of stable collagen VI molecules and subdomains N10-N7 are not required for molecular assembly.