Nasal bone in prenatal trisomy 21 screening

Single nucleotide polymorphism array (SNP-array) analysis for fetuses with abnormal nasal bone

PURPOSE

This study aims to evaluate the prevalence of submicroscopic chromosomal abnormalities found on single nucleotide polymorphism array (SNP array) in pregnancies with either an absent or hypoplastic nasal bone.

METHODS

This retrospective study included 333 fetuses with either nasal bone hypoplasia or absence identified on prenatal ultrasound. SNP array analysis and conventional karyotyping were performed in all the subjects. The prevalence of chromosomal abnormalities was adjusted for maternal age and other ultrasound findings. Fetuses with either an isolated nasal bone absence or hypoplasia, those that had additional soft ultrasound markers, and those where structural defects were found on ultrasound were divided into three groups: A, B, and C, respectively.

RESULTS

Among the total cohort of 333 fetuses, 76 (22.8%) had chromosomal abnormalities, including 47 cases of trisomy 21, 4 cases of trisomy 18, 5 cases of sex chromosome aneuploidy, and 20 cases of copy number variations of which 12 were pathogenic or likely pathogenic. The prevalence of chromosomal abnormalities in group A (n = 164), B (n = 79), and C (n = 90) was 8.5%, 29.1% and 43.3%, respectively. The incremental yields by SNP-array compared with karyotyping in group A, B, and C were 3.0%, 2.5% and 10.7%, respectively (p > 0.05). Compared to karyotype analysis, SNP array detected an additional 2 (1.2%), 1 (1.3%), and 5 (5.6%) pathogenic or likely pathogenic CNVs in groups A, B, and C, respectively. In the 333 fetuses, the prevalence of chromosomal abnormalities in women with advanced maternal age (AMA) was significantly higher than that in non-AMA women, (47.8% vs. 16.5%, p < 0.05).

CONCLUSION

In addition to Down's syndrome, many other chromosomal abnormalities are present in fetuses with abnormal nasal bone. SNP array can improve the prevalence of chromosomal abnormalities associated with nasal bone abnormalities, especially in pregnancies with non-isolated nasal bone abnormalities and advanced maternal age.

Untangle the mystery behind DS-associated AD - Is APP the main protagonist?

Amyloid precursor protein profusion in Trisomy 21, also called Down Syndrome (DS), is rooted in the genetic determination of Alzheimer's disease (AD). With the recent development in patient care, the life expectancy of DS patients has gradually increased, leading to the high prospect of AD development, consequently leading to the development of plaques of amyloid proteins and neurofibrillary tangles made of tau by the fourth decade of the patient leading to dementia. The altered gene expression resulted in cellular dysfunction due to impairment of autophagy, mitochondrial and lysosomal dysfunction, and copy number variation controlled by the additional genes in Trisomy 21. The cognitive impairment and mechanistic insights underlying DS-AD conditions have been reviewed in this article. Some recent findings regarding biomarkers and therapeutics of DS-AD conditions were highlighted in this review.

Nasal bone in fetal aneuploidy risk assessment: are they independent markers in the first and second trimesters?

OBJECTIVES

In the mid-trimester ultrasound, nasal bone (NB) length can be used to correct the a priori risk for trisomy 21. Our study aims to evaluate if there is a correlation between an absent NB in the first trimester and a hypoplastic NB in the second trimester.

METHODS

Our two year retrospective analysis of data derived from routine clinical practice. Single euploid fetuses were included. The NB was assessed in both trimesters according to international guidelines and transformed into categorical variables. Logistic regression was performed in order to accomplish our main objective.

RESULTS

From the 759 normal pregnancies included, 45 (5.93%) had abnormal NB in the first trimester and 23 (3%) in the second trimester. Eleven cases (47.8%) of the abnormal NB in the second trimester were abnormal in the 11-14 weeks scan. After the diagnosis of an absent NB in the first trimester the odds ratio (OR) for a hypoplastic NB in the second trimester is 18.926 (7.791-45.977; p-value <0.01).

CONCLUSIONS

Our data suggest a strong association between the NB in the first and in the second trimester in normal euploid fetuses. This is important information to consider when counseling patients on the basis of this ultrasound marker.

First trimester genetic sonogram for screening fetal Down syndrome: A population-based study

OBJECTIVE

To evaluate the performance of first trimester sonomarkers in the detection of fetal Down syndrome among Thai pregnant women.

MATERIALS AND METHODS

Pregnant women at 11-13⁺⁶ weeks' gestation underwent ultrasound examination for assessment of nuchal translucency (NT), nasal bone (NB), tricuspid regurgitation (TR), and abnormal ductus venosus (aDV) Doppler waveforms. The women were followed up for final outcomes. Fetal abnormalities other than trisomy 21 were excluded. The performances of each sonomarker and their combinations in predicting fetal Down syndrome were calculated.

RESULTS

A total of 7820 pregnant women meeting the inclusion criteria were available for analysis, including 20 cases with fetal Down syndrome and 7800 unaffected cases. Of the four sonomarkers, NT, as a single sonomarker, had the highest detection rate (55.0% at a false positive rate of about 5%), whereas the remaining single sonomarkers had low detection rate (15-20%). The combination of all sonomarkers had the highest detection rate of 70% but the false positive rate was as high as 10.8%. The combination of NT and NB had a detection rate of 60% with an acceptable false positive rate of 6.9%, whereas the other combinations yielded relatively high false positive rates.

CONCLUSION

The first trimester genetic sonogram in screening for Down syndrome among Asian women is acceptably effective and may be offered to some selected groups of the population. NT is the best sonomarker with a detection rate of 55% at 5% false positive rate and its combination with NB can improve performance with minimal increase in false positive rate.

Absent fetal nasal bone in the second trimester and risk of abnormal karyotype in a prescreened population of Chinese women

INTRODUCTION

The aim of this study was to evaluate the value of absent fetal nasal bone in the prediction of fetal chromosomal abnormalities, according to whether it was associated with other soft markers or structural abnormalities in a prescreened population of Chinese pregnant women.

MATERIAL AND METHODS

In this retrospective cohort study, women whose fetuses had absent nasal bone detected during the second trimester ultrasound scan were followed. Fetal karyotyping was performed and pregnancy outcomes were recorded. The association between absent fetal nasal bone with abnormal karyotype was evaluated according to whether soft markers or structural abnormalities were also observed.

RESULTS

Fetal nasal bone was assessed in 56 707 singleton pregnancies. After exclusion of unqualified cases, 71 (71/56 707, 0.13%) fetuses were included in the final analyses, of which 16 (16/71, 22.54%) were detected to have chromosomal abnormalities, including 12 cases of trisomy-21, three of trisomy-18, and one of micro-deletion (in 7q). Among the 42 cases with isolated absence of nasal bone, two had trisomy-21 and one had a micro-deletion. Absence of nasal bone in association with other structural abnormalities had a higher rate of abnormal karyotypes compared with isolated absence of nasal bone [83.33% (10/12) vs. 7.14% (3/42), Fisher's exact test χ²  = 25.620, p < 0.001].

CONCLUSION

Absent fetal nasal bone is a highly specific ultrasonographic soft marker that should be included in the routine second trimester ultrasound scan.

Frontal space distance in facial clefts and retrognathia at 11-13 weeks' gestation

OBJECTIVE

To examine the frontal space (FS) distance in first-trimester fetuses with bilateral, unilateral or median cleft lip and palate and in those with retrognathia.

METHODS

This was a retrospective study using stored two-dimensional ultrasound images of fetal profiles that were recorded at the time of the nuchal translucency (NT) scan at three prenatal medical centers. Images of 300 normal fetuses and 53 fetuses with facial defects were obtained. To measure the FS distance, a line was drawn between the anterior edge of the mental protuberance of the mandible and anterior edge of the maxilla (MM line) and extended upwards in front of the forehead. The perpendicular distance (FS distance) between the MM line and the skin at the point of largest excursion of the fetal forehead was measured. In cases in which the MM line was located anteriorly to the forehead, the distance was measured in the same fashion but was multiplied by -1. Two operators measured the FS distance twice, independently of each other. FS distances were transformed into Z-scores based on the linear relationship with crown-rump length (CRL) in normal fetuses. The distribution of FS distances in fetuses with bilateral, unilateral or median cleft lip and palate and those with retrognathia were compared with that in the normal group using Student's t-test.

RESULTS

A search of the centers' databases identified 53 abnormal cases including 20, nine and eight with a bilateral, unilateral and median cleft lip and palate, respectively, and 16 cases of retrognathia. In fetuses with bilateral, unilateral and median clefts and those with retrognathia, median delta NT was 1.00 mm, 0.37 mm, 4.00 mm and 0.26 mm, respectively. Among these affected groups, 12 (60.0%), six (66.7%), two (25.0%) and eight (50.0%) fetuses had an abnormal karyotype. In the normal population, FS distance was dependent on CRL measurement (FS = 6.62 - (0.08 × CRL); r = -0.539; P < 0.0001). In fetuses with a bilateral and median cleft and in those with retrognathia, FS distance was significantly different from that in the normal population (all P < 0.0001), however, the difference was not significant in fetuses with unilateral clefts (P = 0.103). The respective Z-scores of FS distance for fetuses with bilateral, unilateral and median clefts and retrognathia were -9.7 ± 2.0, -3.1 ± 5.1, 8.2 ± 3.4 and -7.3 ± 2.3. Measurements were ≥ 99(th) and ≤ 1(st) centiles in all but one (98.1%) case.

CONCLUSION

The FS distance appears to be a helpful tool in the detection of facial clefts at 11-13 weeks' gestation. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

Prefrontal space ratio in second- and third-trimester screening for trisomy 21

OBJECTIVE

To evaluate the prefrontal space ratio (PFSR) in second- and third-trimester euploid fetuses and fetuses with trisomy 21.

METHODS

This was a retrospective study utilizing stored mid-sagittal two-dimensional images of second- and third-trimester fetal faces that were recorded during prenatal ultrasound examinations at the Department of Prenatal Medicine at the University of Tuebingen, Germany and at a private center for prenatal medicine in Nuremberg, Germany. For the normal range, 279 euploid pregnancies between 15 and 40 weeks' gestation were included. The results were compared with 91 cases with trisomy 21 between 15 and 40 weeks. For the ratio measurement, a line was drawn between the leading edge of the mandible and the maxilla (MM line) and extended in front of the forehead. The ratio of the distance between the leading edge of the skull and the leading edge of the skin (d1) to the distance between the skin and the point where the MM line was intercepted (d2) was calculated. The PFSR was determined by dividing d2 by d1.

RESULTS

In the euploid and trisomy 21 groups, the median gestational age at the time of ultrasound examination was 21.1 (range, 15.0-40.0) and 21.4 (range, 15.0-40.3) weeks, respectively. Multiple regression analysis showed that PFSR was independent of maternal and gestational age. In the euploid group, the mean PFSR was 0.97 ± 0.29. In fetuses with trisomy 21, the mean PFSR was 0.2 ± 0.38 (P < 0.0001). The PFSR was below the 5(th) centile in 14 (5.0%) euploid fetuses and in 72 (79.1%) fetuses with trisomy 21.

CONCLUSION

The PFSR is a simple and effective marker in second- and third-trimester screening for trisomy 21.

Neurobiological elements of cognitive dysfunction in down syndrome: exploring the role of APP

Down syndrome (DS) is the most common cause of cognitive dysfunction in children. Additionally, most adults with DS will eventually show both clinical and neuropathologic hallmarks of Alzheimer's disease (AD). The hippocampal formation constitutes the primary target for degeneration in both AD and DS. Over the past few years, we have studied the molecular mechanisms behind degeneration of this region and its major inputs in mouse models of DS. Our investigation has suggested that the loss of hippocampal inputs, particularly cholinergic and noradrenergic terminals, leads to de-afferentation of this region in the Ts65Dn mouse model of DS. Interestingly, we were able to link the overexpression of amyloid precursor protein (App) gene to degeneration of cholinergic and noradrenergic neurons in DS mouse models. We examined the underlying mechanisms of degeneration of multiple systems with extensive projections to the hippocampus in DS and its mouse models and the role of App overexpression in neurodegeneration. Understanding mechanisms behind hippocampal dysfunction has helped us to test several therapeutic strategies successfully in mouse models of DS. Here we review these strategies and mechanisms and discuss ways to translate our findings into possible interventions in humans.

Assessment of the ductus venosus, tricuspid blood flow and the nasal bone in second-trimester screening for trisomy 21

OBJECTIVE

To examine the prevalence of reversed a-wave in the ductus venosus, tricuspid regurgitation and absent nasal bone, in a second-trimester population undergoing amniocentesis, after exclusion of major fetal defects and to estimate the performance in screening for trisomy 21 based on maternal age and these markers in a general population.

METHODS

This was a retrospective study involving pregnancies undergoing amniocentesis due to increased risk for trisomy 21, mainly because of advanced maternal age. Before the invasive procedure, an ultrasound examination was carried out to exclude major fetal defects and to examine the ductus venosus, tricuspid blood flow and the presence of the fetal nasal bone. Modeling techniques were used based on 20 000 euploid pregnancies and 20 000 pregnancies with trisomy 21 to assess the screening performance in a general population.

RESULTS

The study population consisted of 3613 euploid pregnancies and 35 cases with trisomy 21. In the euploid group, reversed flow in the ductus venosus, tricuspid regurgitation and an absent nasal bone was observed in 1.7%, 1.5% and 0.1% of cases, respectively. In the trisomic group, these markers were found in 14.3%, 11.4% and 14.3% of cases, respectively. For a 5% false-positive rate, the detection rate in screening for trisomy 21, based on maternal age and either ductus venosus, tricuspid blood flow or nasal bone would be 33.8%, 32.4% or 31.4%, respectively. Screening by maternal age alone would detect 29.0% of the fetuses with trisomy 21. Receiver-operating characteristics curve analysis showed a slight but significant improvement in screening performance for trisomy 21 based on the inclusion of these markers.

CONCLUSION

Second-trimester ultrasound screening for trisomy 21 based on maternal age with additional assessment of the ductus venosus, tricuspid blood flow and the fetal nasal bone in otherwise normal-appearing fetuses is only marginally better than is screening by maternal age alone.