Increased NCAM expression and vascular development in trisomy 16 mouse embryos: relationship with nuchal translucency

Involvement of neurons and retinoic acid in lymphatic development: new insights in increased nuchal translucency

OBJECTIVE

Increased nuchal translucency originates from disturbed lymphatic development. Abnormal neural crest cell (NCC) migration may be involved in lymphatic development. Because both neuronal and lymphatic development share retinoic acid (RA) as a common factor, this study investigated the involvement of NCCs and RA in specific steps in lymphatic endothelial cell (LEC) differentiation and nuchal edema, which is the morphological equivalent of increased nuchal translucency.

METHODS

Mouse embryos in which all NCCs were fluorescently labeled (Wnt1-Cre;Rosa26(eYfp) ), reporter embryos for in vivo RA activity (DR5-luciferase) and embryos with absent (Raldh2(-/-) ) or in utero inhibition of RA signaling (BMS493) were investigated. Immunofluorescence using markers for blood vessels, lymphatic endothelium and neurons was applied. Flow cytometry was performed to measure specific LEC populations.

RESULTS

Cranial nerves were consistently close to the jugular lymph sac (JLS), in which NCCs were identified. In the absence of RA synthesis, enlarged JLS and nuchal edema were observed. Inhibiting RA signaling in utero resulted in a significantly higher amount of precursor-LECs at the expense of mature LECs and caused nuchal edema.

CONCLUSIONS

Neural crest cells are involved in lymphatic development. RA is required for differentiation into mature LECs. Blocking RA signaling in mouse embryos results in abnormal lymphatic development and nuchal edema.

Development of secondary lymphoid organs in relation to lymphatic vasculature

Although the initial event in lymphatic endothelial specification occurs slightly before the initiation of lymph node formation in mice, the development of lymphatic vessels and lymph nodes occurs within the same embryonic time frame. Specification of lymphatic endothelial cells starts around embryonic day 10 (E10), followed by endothelial cell budding and formation of the first lymphatic structures. Through lymphatic endothelial cell sprouting these lymph sacs give rise to the lymphatic vasculature which is complete by E15.5 in mice. It is within this time frame that lymph node formation is initiated and the first structure is secured in place. As lymphatic vessels are crucially involved in the functionality of the lymph nodes, the recent insight that both structures depend on common developmental signals for their initiation provides a molecular mechanism for their coordinated formation. Here, we will describe the common developmental signals needed to properly start the formation of lymphatic vessels and lymph nodes and their interdependence in adult life.

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.

First-trimester measurement of the ductus venosus pulsatility index and the prediction of congenital heart defects

OBJECTIVE

This study was carried out to evaluate the additional predictive value of ductus venosus pulsatility index for veins (DV-PIV) in the identification of congenital heart defects (CHDs) in fetuses with an enlarged nuchal translucency (NT) and a normal karyotype.

METHODS

All chromosomally normal fetuses referred to our Fetal Medicine Unit between September 1996 and December 2008 with known NT, DV-PIV and ductus venosus (DV) a-wave measurements were included. Intrafetus variation in DV-PIV was overcome by averaging three recordings. Follow-up included special focus on CHD. The odds of CHD at any NT and DV-PIV value were evaluated using logistic regression analysis.

RESULTS

Of 792 fetuses included, the NT was enlarged (equal to or above the 95(th) percentile (P95)) in 318 (40.2%). The DV-PIV was abnormal (≥ P95) in 41.8% of the fetuses with an enlarged NT and the a-wave was abnormal (negative or reversed) in 29.9%. CHD was diagnosed in 35 fetuses, 33 of which had an enlarged NT. Amongst the fetuses with an enlarged NT, the sensitivities for CHD of abnormal DV-PIV and DV a-wave were 73% and 55%, with specificities of 62% and 73%, respectively. Logistic regression analysis showed that in this risk group the DV-PIV multiple of the median (MoM) (as a continuous variable) was significantly associated with the risk of CHD (odds ratio = 2.4), independent of the degree of NT enlargement, whereas the DV a-wave did not significantly add to the prediction of CHD.

CONCLUSION

Two-thirds of fetuses with an enlarged NT, a normal karyotype and CHD have an increased DV-PIV. DV-PIV can be used as continuous variable in combination with NT to increase specificity in the identification of CHD and to refine the individual risk assessment.

New insights into the development of lymphoid tissues

Secondary lymphoid organs are important locations for the initiation of adaptive immune responses. They develop before birth, and their formation requires interaction between lymphotoxin-α₁ß₂-expressing lymphoid-tissue inducer cells and lymphotoxin-ß receptor-expressing stromal organizer cells. Here, we discuss new insights into the earliest phases of peripheral lymph node and Peyer's patch formation that occur before lymphotoxin-ß receptor signalling and suggest a role for the developing nervous system. In addition, we discuss the differing requirements for the postnatal formation of mucosa-associated lymphoid tissues and tertiary lymphoid structures that develop at sites of chronic inflammation.

Altered jugular vein and ductus venosus flow velocities in fetuses with increased nuchal translucency and distended jugular lymphatic sacs

OBJECTIVE

We sought to assess blood flow in relation to jugular lymphatic distension in fetuses with increased and normal nuchal translucency (NT).

STUDY DESIGN

In all, 72 fetuses with normal NT and 71 fetuses with NT >95th percentile were evaluated. NT size, jugular lymphatic sacs (JLS), jugular vein and ductus venosus pulsatility index for veins (PIV), and intracardiac velocities were measured.

RESULTS

JLS were visualized in 22/72 fetuses with normal and in 55/71 fetuses with increased NT. Jugular vein and ductus venosus PIV was higher in fetuses with increased NT compared to normal NT (P < .01). Visibility of JLS was associated with a higher ductus venous PIV (P < .05), but not with a higher jugular vein PIV. Larger NT and larger JLS volumes were associated with higher jugular vein and ductus venosus PIV (P < .05).

CONCLUSION

This study shows a relation among increased NT, jugular lymphatic distension, and altered blood flow in jugular vein and ductus venosus.

Abnormal Shh and FOXC2 expression correlates with aberrant lymphatic development in human fetuses with increased nuchal translucency

OBJECTIVE

Previous research in fetuses with increased nuchal translucency (NT) showed abnormal lymphatic endothelial differentiation characteristics, including increased vascular endothelial growth factor (VEGF)-A expression, and aberrant smooth muscle cells (SMCs) surrounding enlarged jugular lymphatic sacs (JLS). We hypothesized that abnormal Sonic hedgehog (Shh) expression would result in altered VEGF-A signaling in the lymphatic endothelial cells of the JLS and that aberrant acquisition of SMCs could be caused by downregulation of forkhead transcription factor FOXC2 and upregulation of platelet-derived growth factor (PDGF)-B in the lymphatic endothelial cells of the JLS.

METHODS

Five trisomy 21 fetuses and four controls were investigated using immunohistochemistry for Shh, VEGF-A, FOXC2 and PDGF-B expression in the lymphatic endothelial cells of the JLS.

RESULTS

An increased Shh, VEGF-A and PDGF-B expression, and decreased FOXC2 expression were shown in the lymphatic endothelial cells of the JLS of the trisomic fetuses.

CONCLUSIONS

Increased Shh and VEGF-A expression is correlated with an aberrant lymphatic endothelial differentiation in trisomy 21 fetuses. The SMCs surrounding the JLS can possibly be explained by an increase of PDGF-B-induced SMC recruitment and/or differentiation. This underscores earlier findings that indicate the loss of lymphatic identity in trisomy 21 fetuses and a shift towards a blood vessel wall phenotype.

The nuchal translucency and the fetal heart: a literature review

In this overview the current knowledge of the relationship between an increased nuchal translucency (NT) measurement and fetal heart structure and function in chromosomally normal fetuses is reviewed. Relevant pathophysiological theories behind the increased NT are discussed. Fetuses with an increased NT have an increased risk for congenital heart disease (CHD) with no particular bias for one form of CHD over another. This risk increases with increasing NT measurement. Although the NT measurement is only a modestly effective screening tool for all CHD when used alone, it may indeed be effective in identifying specific CHD "likely to benefit" from prenatal diagnosis. The combination of an increased NT, tricuspid regurgitation and an abnormal ductus venosus (DV) Doppler flow profile, is a strong marker for CHD. A fetal echocardiogram should be performed at 20 weeks' gestation in fetuses with an NT > or = 95th percentile but < 99th percentile. When the NT measurement is > or = 99th percentile, or when tricuspid regurgitation and/or an abnormal DV flow pattern is found along with the increased NT, an earlier echocardiogram is indicated, followed by a repeat scan at around 20 weeks' gestation. The resultant increased demand for early fetal echocardiography and sonographers with this special expertise needs to be planned and provided for.

Inner Ear Dysplasia is Common in Children With Down Syndrome (trisomy 21)

OBJECTIVES/HYPOTHESIS

Middle and external ear anomalies are well recognized in Down syndrome (DS, trisomy 21). Inner ear anomalies are much less frequently described. This study reviews inner ear morphology on imaging to determine the prevalence of cochlear and vestibular anomalies in children with DS.

STUDY DESIGN

The authors conducted a retrospective review of imaging features of (DS) inner ear structures.

METHODS

Fifty-nine sequential patients with DS with imaging of the inner ear were identified by a radiology report text search program. Quantitative biometric assessment of the inner ear was performed on patients with high-resolution computed tomography or magnetic resonance images of the petrous bone. Petrous imaging was performed for evaluation of inflammatory disease or hearing loss. Spinal imaging, which included petrous views, was performed in most cases to exclude C1 to 2 dislocation, a potential complication of DS. Measurements were compared with normative data.

RESULTS

Inner ear dysplasia is much more common in DS than previously reported. Inner ear structures are universally hypoplastic. Vestibular malformations are particularly common and a small bony island of the lateral semicircular canal (<3 mm in diameter) appears highly typical. Additional findings in some patients were persistent lateral semicircular anlage with fusion of the lateral semicircular canal and vestibule into a single cavity, vestibular aqueduct and endolymphatic sac fossa enlargement, cochlear nerve canal hypoplasia, and stenosis or duplication of the internal auditory canal. Stenosis of the external meatus, poor mastoid pneumatization, middle ear and mastoid opacification, and cholesteatoma were common, as expected.

Temporal Relationship Between Increased Nuchal Translucency and Enlarged Jugular Lymphatic Sac

OBJECTIVE

To study the relationship between the volume of the jugular lymphatic sacs and nuchal translucency thickness in fetuses with increased nuchal translucency with advancing gestation.

METHODS

Seventy-four fetuses with a nuchal translucency greater than the 95th percentile were examined weekly between 11 and 17 weeks of gestational age. The fetal neck region was studied by ultrasonography, followed by measurement of nuchal translucency and jugular lymphatic sacs. The measurements were analyzed using multilevel analysis. In case of termination of pregnancy postmortem examination was performed.

RESULTS

In 40 euploid fetuses and 34 aneuploid fetuses, 159 measurements of jugular lymphatic sac volume and nuchal translucency thickness were analyzed. The volume of the jugular lymphatic sacs and gestational age showed a quadratic relation, which differed between euploid and aneuploid fetuses (P < .01). The maximum volumes were larger and present longer in fetuses with aneuploidy than in euploid fetuses (P < .01). In case of a cardiac anomaly, jugular lymphatic sac volume was larger than in cardiac normal fetuses (nonsignificant). Furthermore, the development of jugular lymphatic sac volume and increased nuchal translucency were related, whereby an increase of the nuchal translucency preceded enlargement of the jugular lymphatic sacs (P < .001). In each fetus an increase in jugular lymphatic sac volume was followed by a decrease with advancing gestation. The gestational age at maximum jugular lymphatic sac volume differed between fetuses, indicating a fetus-specific pattern. Nuchal translucency development showed a similar pattern. Postmortem examination confirmed distension of the jugular lymphatic sacs in all cases.

CONCLUSION

Increased nuchal translucency is associated with abnormal lymphatic development, in which nuchal translucency enlargement precedes enlargement of jugular lymphatic sacs on ultrasound examination. Aneuploid fetuses have a more disturbed lymph angiogenesis.

LEVEL OF EVIDENCE

III.

Nuchal edema and venous-lymphatic phenotype disturbance in human fetuses and mouse embryos with aneuploidy

OBJECTIVE

Nuchal edema (NE) is a clinical indicator for aneuploidy, cardiovascular anomalies, and several genetic syndromes. Its etiology, however, is unknown. In the nuchal area, the endothelium of the jugular lymphatic sacs (JLS) develops by budding from the blood vascular endothelium of the cardinal veins. Abnormal distension of the jugular sacs is associated with NE. We hypothesize that a disturbed lymphatic endothelial differentiation and sac formation causes NE. We investigated endothelial differentiation of the jugular lymphatic system in human and mouse species with NE.

METHODS

Aneuploid human fetuses (trisomy 21; trisomy 18) were compared with euploid controls (gestational age 12 to 18 weeks). Trisomy 16 mouse embryos were compared with wild type controls (embryonic day 10 to 18). Trisomy 16 mice are considered an animal model for human trisomy 21. Endothelial differentiation was investigated by immunohistochemistry using lymphatic markers (prox-1, podoplanin, lymphatic vessel endothelial hyaluronan receptor [LYVE]-1) and en blood vessel markers (neuropilin [NP]-1 and ligand vascular endothelial growth factor [VEGF]-A). Smooth muscle actin (SMA) was included as a smooth muscle cell marker.

RESULTS

We report a disturbed venous-lymphatic phenotype in aneuploid human fetuses and mouse embryos with enlarged jugular sacs and NE. Our results show absent or diminished expression of the lymphatic markers Prox-1 and podoplanin in the enlarged jugular sac, while LYVE-1 expression was normal. Additionally, the enlarged JLS showed blood vessel characteristics, including increased NP-1 and VEGF-A expression. The lumen contained blood cells and smooth muscle cells lined the wall.

CONCLUSION

A loss of lymphatic identity seems to be the underlying cause for clinical NE. Also, abnormal endothelial differentiation provides a link to the cardiovascular anomalies associated with NE.