Prenatal screening for trisomy 18 with free beta human chorionic gonadotrophin as a marker.

OBJECTIVE--To determine the relation between maternal serum alpha fetoprotein and free beta human chorionic gonadotrophin concentrations in pregnancies complicated by trisomy 18 and establish whether prenatal biochemical screening for this condition could be developed in a way similar to that proposed for trisomy 21. DESIGN--Serum alpha fetoprotein and free beta human chorionic gonadotrophin concentrations in women with singleton pregnancies affected by cytogenetically confirmed trisomy 18, uncomplicated by neural tube defect or ventral wall defect, were identified from prospective trisomy 21 screening programmes. Additionally, stored maternal serum from similar pregnancies was analysed retrospectively. Analyte concentrations from singleton unaffected pregnancies were identified from a prospective screening programme as controls. Statistical parameters of the affected and unaffected populations were compiled. SETTING--Biochemical screening laboratories in Britain and the United States. SUBJECTS--52 women with singleton pregnancies complicated by trisomy 18; control population of 6661 women with unaffected singleton pregnancies. MAIN OUTCOME MEASURES--Median values of each analyte and their distribution in the affected and unaffected populations; detection rate of trisomy 18 and the false positive rate. RESULTS--Maternal serum alpha fetoprotein and free beta human chorionic gonadotrophin concentrations were significantly lower in pregnancies complicated by trisomy 18 (median values 0.71 and 0.37 respectively). By using a multivariate risk algorithm incorporating maternal age risk of trisomy 18 and the concentration of the two biochemical markers it was predicted that 50% of trisomy 18 cases (unaffected by neural tube defect or ventral wall defect) could be detected with a 1% false positive rate. CONCLUSION--Second trimester biochemical screening for trisomy 18 could be a valuable addition to trisomy 21 screening programmes.     

Contribution of ultrasonographic examination to the prenatal detection of trisomy 21: experience from 19 European registers

The objective of this study was to evaluate the contribution of ultrasound scanning to the prenatal detection of trisomy 21 in a large unselected European population. Data from 19 congenital malformation registers in 11 European countries were included. The prenatal ultrasound screening programs in the countries ranged from no routine screening to three ultrasound investigations per patient. Routine serum screening was offered in four of the 11 countries and routine screening on the basis of maternal age amniocentesis in all. The results show that overall 53% of cases of trisomy 21 were detected prenatally with a range from 3% in Lithuania to 88% in Paris. Ninety-eight percent of women whose babies were diagnosed before 24 weeks gestation chose to terminate the pregnancy. Centres/countries that offer serum screening do not have a significantly higher detection rate of trisomy 21 when compared to those that offer maternal age amniocentesis and anomaly scanning only. Fifty percent of trisomy 21 cases were born to women aged 35 years or more. In conclusions, second trimester ultrasound plays an important role in the prenatal diagnosis of trisomy 21. Of those cases prenatally diagnosed, 64% of cases in women <35 years and 36% of those in women >or=35 years were detected because of an ultrasound finding. Ultrasound soft markers accounted for 84% of the scan diagnoses. There is evidence of increasing maternal age across Europe with 50% of cases of trisomy 21 born to women aged 35 years or more.     

Fetal nuchal translucency thickness

In the early 1990s Nicolaides introduced screening for trisomy 21 by fetal nuchal translucency thickness measurement with ultrasound between 11-13(+6) weeks. Already in 1866 L. Down noted that common features of patients with trisomy 21 are a skin being too large for the body and a flat face with a small nose. While detection rates for trisomy 21, given an invasive testing rate of 5%, were only 30% for screening by maternal age and 65% for screening by maternal serum triple test, the detection rate for screening by nuchal translucency combined with maternal age was 75% and this could be increased to 90% in combination with maternal serum screening (serum B-human chorionic gonadotropin and pregnancy-associated plasma protein-A) at 11-13(+6) weeks. The additional soft markers in the first trimester are the fetal nasal bone, the Doppler velocity waveform in the ductus venosus and tricuspid regurgitation and these markers can be used to further increase the detection rate of trisomy 21. In addition increased nuchal translucency thickness can also identify other chromosomal defects (mainly trisomy 13 and 18 and monosomy X) and major congenital malformations (mainly cardiac defects) and genetic syndromes.     

Two-dimensional gel analysis of proteins from human trisomy 21 fetal liver tissue after DEAE-Sepharose chromatography

Summary Isoelectrofocusing two-dimensional polyacrylamide gel electrophoresis (IEF-2D-PAGE) offers the opportunity to detect typical alterations in the protein pattern from directly prepared liver tissue of fetuses with trisomy 21 and normal controls. The fractionation of the cell lysate by differential centrifugation into various subcellular components (nuclei, membranes, polyribosomes, cytoplasmic proteins) and fractionation of the proteins through DEAE-Sepharose chromatography allows detection of protein differences. In the 19th week of pregnancy it is possible to establish only three differences in the protein patterns between liver tissue from trisomy 21-fetuses and normal controls. All three proteins are synthesized in euploid controls at a higher level than in trisomy 21-liver tissue and are supposed to be consequences of primary gene dosage effects. The molecular mass of the individual proteins ranges from 14 kdaltons to 31 kdaltons. The data reported here raise the question whether some of the differences found by others represent different gene expression of cells under tissue culture conditions and/or of cells derived from different tissues, or developmental stages.     

Parental origin of the extra chromosome in prenatally diagnosed fetal trisomy 21

Trisomy 21 (Down syndrome) is one of the most common chromosomal abnormalities. Of cases of free trisomy 21 causing Down syndrome, about 95% result from nondisjunction during meiosis, and about 5% are due to mitotic errors in somatic cells. Previous studies using DNA polymorphisms of chromosome 21 showed that paternal origin of trisomy 21 occurred in only 6.7% of cases. However, these studies were conducted in liveborn trisomy 21-affected infants, and the possible impact of fetal death was not taken into account. Using nine distinct DNA polymorphisms, we tested 110 families with a prenatally diagnosed trisomy 21 fetus. Of the 102 informative cases, parental origin was maternal in 91 cases (89.2%) and paternal in 11 (10.8%). This percentage differs significantly from the 7.0% observed in previous studies (P<0.001). In order to test the influence of genomic parental imprinting, we determined the origin of the extra chromosome 21 in relation to different factors: advanced maternal age, maternal serum human chorionic gonadotropin (hormone of placental origin), severity of the disease, gestational age at diagnosis and fetal gender. We found that the increased frequency of paternal origin of nondisjunction in trisomy 21-affected fetuses cannot obviously be explained by factors leading to selective loss of paternal origin fetuses.     

A maternal serum screen for trisomy 18: an extension of maternal serum screening for Down syndrome.

The feasibility of extending second-trimester maternal blood screening for Down syndrome so as to include screening for trisomy 18 was examined using stored maternal serum samples collected for neural tube-defect screening. There were 12 samples from trisomy 18 pregnancies and 390 controls. The median maternal serum concentration of alpha-fetoprotein, free alpha-subunit human chorionic gonadotrophin, free beta-subunit human chorionic gonadotrophin, intact human chorionic gonadotrophin, total estriol, unconjugated estriol, estradiol, human placental lactogen, and progesterone were lowered in those pregnancies affected by trisomy 18 when compared with unaffected pregnancies matched for racial origin, maternal age, gestational age, and sample-storage duration. At an estimated odds risk of 1:400, 83.3% of affected pregnancies were detected using an algorithm which combines the maternal age-related risk with the maternal serum concentrations of unconjugated estriol, free alpha-subunit human chorionic gonadotrophin, free beta-subunit human chorionic gonadotrophin, estradiol, and human placental lactogen. The associated false-positive rate was 2.6%. At high risk odds of 1:10, the detection rate was 58.3%, with an associated false-positive rate of 0.3%. beta-Subunit human chorionic gonadotrophin and unconjugated estriol were the most powerful discriminators. It is possible to incorporate into existing Down syndrome screening programs an algorithm for detecting trisomy 18 with high sensitivity and specificity.     

Biochemical screening of fetal aneuploidies and neural tube defects by "double-test" in Croatia: a 10 years' experience

The aim of the study is to investigate the efficiency of the second-trimester biochemical screening, with maternal serum alpha-fetoprotein (MS-AFP) and free beta-subunit of human chorionic gonadotropin (free beta-hCG), during the ten-year period. The study included 11,292 of pregnant women between the 15th and 18th gestational week, who underwent screening from November 1996 to December 2006. The risk for trisomy 21 and trisomy 18 were calculated by computer software, based on a model which generated the final risk for fetal aneuploidies from the pregnant woman's a priori age risk and the likelihood ratio of the distribution of the biochemical markers, according to the second-trimester gestation. With the cut-off value of the final risk > or = 1:250, the detection rate for trisomy 21 was 75% (21/28). In women less than or equal to 35, the detection was 57.1% (8/14) and 92.9% (13/14) in those over 35 years, respectively. The detection rate of trisomy 18 was 50% (2/4). The results confirmed that the implementation of double-test, as non-invasive screening for fetal aneuploidies, should be accepted as a complementary method of antenatal care.     

Familial Down's syndrome.

A family is reported in which the same mother conceived two children with trisomy 21. The pregnancy with the second affected child was interrupted after diagnostic amniocentesis. Maternal chromosome analysis was normal. This family and those previously reported suggest that there is an increased recurrence risk of trisomy 21 after the birth of an affected individual, possibly caused by a genetic tendency for non-disjunction. After the birth of a child with Down's syndrome, amniocentesis and chromosome analysis of cultured amniotic fluid cells is indicated in each further pregnancy, irrespective of maternal age.     

First trimester screening for trisomy 21 in gestational week 8-10 by ADAM12-S as a maternal serum marker

Background  

A disintegrin and metalloprotease 12 (ADAM12-S) has previously been reported to be significantly reduced in maternal serum from women with fetal aneuploidy early in the first trimester and to significantly improve the quality of risk assessment for fetal trisomy 21 in prenatal screening. The aim of this study was to determine whether ADAM12-S is a useful serum marker for fetal trisomy 21 using the mixture model.     

Maternal balanced translocation (4;21) leading to an offspring with partial duplication of 4q and 21q without phenotypic manifestations of Down syndrome

We describe an 8-years old female with supernumerary chromosome der(21)t(4;21)(q25;q22) resulting in partial trisomy 4q25-qter and partial trisomy 21(pter-q22). The extra material was originated from a reciprocal balanced translocation carrier mother (4q;21q). Karyotyping was confirmed by FISH using whole chromosome painting probes for 4 and 21q and using 21q22.13-q22.2 specific probe to rule out trisomy of Down syndrome critical region. Phenotypic and cytogenetic findings were compared with previously published cases of partial trisomy 4q and 21q. Our patient had the major criteria of distal trisomy 4q namely severe psychomotor retardation, growth retardation, microcephaly, hearing impairment, specific facies (broad nasal root, hypertelorism, ptosis, narrow palpebral fissures, long eye lashes, long philtrum, carp like mouth and malformed ears) and thumbs and minor feet anomalies. In spite of detection of most of the 3 copies of chromosome 21, specific features of Down syndrome (DS) were lacked in this patient, except for notable bilateral symmetrical calcification of basal ganglia. This report represents further delineation of the phenotype-genotype correlation of trisomy 4q syndrome. It also supports that DS phenotype is closely linked to 21q22. Nevertheless, presence of basal ganglia calcification in this patient may point out to a more proximal region contributing in its development in DS, or that genes outside the critical region may influence or control manifestations of DS features.     

Maternal serum cell-free fetal DNA levels are increased in cases of trisomy 13 but not trisomy 18

Cell-free fetal DNA in the maternal circulation is a potential noninvasive marker for fetal aneuploidies. In previous studies with Y DNA as a fetal-specific marker, levels of circulating fetal DNA were shown to be elevated in women carrying trisomy 21 fetuses. The goal of this study was to determine whether cell-free fetal DNA levels in the serum of pregnant women carrying fetuses with trisomies 13 or 18 are also elevated. Archived maternal serum samples from five cases of male trisomy 13 and five cases of male trisomy 18 were studied. Each case was matched for fetal gender, gestational age, and duration of freezer storage to four or five control serum samples presumed to be euploid after newborn medical record review. Real-time quantitative polymerase chain reaction amplification of DYS1 was performed to measure the amount of male fetal DNA present. Unadjusted median serum fetal DNA concentrations were 97.5 GE/ml (genomic equivalents per milliliter; 29.2-187.0) for the trisomy 13 cases, 31.5 GE/ml (18.6-77.6) for the trisomy 18 cases, and 40.3 GE/ml (3.7-127.4) for the controls. Fetal DNA levels in trisomy 13 cases were significantly elevated ( P=0.016) by analysis of variance of the ranks of values within each matched set. In contrast, fetal DNA levels in trisomy 18 cases were no different from the controls ( P=0.244). Second trimester maternal serum analytes currently used in screening do not identify fetuses at high risk for trisomy 13. Fetal DNA may facilitate noninvasive screening for trisomy 13 provided that a gender-independent fetal DNA marker can be developed.     

Prenatal diagnosis of trisomy 21: registration results from a single genetic center

This is a retrospective review of all collected amniotic fluid samples, chorionic villus samples and other fluid-aspirations (hygroma colli fluid/urine from megacystis) over an 11-year period (1996-2006) in a single Genetic Center (University Hospital Gasthuisberg, Leuven), looking at the prenatal diagnosis of trisomy 21. In this study a total of 404 diagnoses of trisomy 21 were made on 29696 samples (1.4%). The prenatal diagnosis of trisomy 21 increased over the years with 0.88% (21/2363) in 1996 and 1.99% (50/2512)in 2006. Also the type of invasive testing changed over the years with an increase of the proportion of trisomy 21- diagnoses by chorionic villussampling from 2001. Looking at the registry for perinatal activities in Flanders for the year 2006 the live birth incidence for trisomy 21 was 1/1782 and this is lower than the often reported incidence oftrisomy 21 at birth of 1/800: it is likely that the use of more sensitive screening methods for the prenatal detection of trisomy 21 and the election of termination for most affected pregnancies affects the birth incidence oftrisomy 21.     

Human microRNA-155 on chromosome 21 differentially interacts with its polymorphic target in the AGTR1 3' untranslated region: a mechanism for functional single-nucleotide polymorphisms related to phenotypes

Animal microRNAs (miRNAs) regulate gene expression through base pairing to their targets within the 3' untranslated region (UTR) of protein-coding genes. Single-nucleotide polymorphisms (SNPs) located within such target sites can affect miRNA regulation. We mapped annotated SNPs onto a collection of experimentally supported human miRNA targets. Of the 143 experimentally supported human target sites, 9 contain 12 SNPs. We further experimentally investigated one of these target sites for hsa-miR-155, within the 3' UTR of the human AGTR1 gene that contains SNP rs5186. Using reporter silencing assays, we show that hsa-miR-155 down-regulates the expression of only the 1166A, and not the 1166C, allele of rs5186. Remarkably, the 1166C allele has been associated with hypertension in many studies. Thus, the 1166C allele may be functionally associated with hypertension by abrogating regulation by hsa-miR-155, thereby elevating AGTR1 levels. Since hsa-miR-155 is on chromosome 21, we hypothesize that the observed lower blood pressure in trisomy 21 is partially caused by the overexpression of hsa-miR-155 leading to allele-specific underexpression of AGTR1. Indeed, we have shown in fibroblasts from monozygotic twins discordant for trisomy 21 that levels of AGTR1 protein are lower in trisomy 21.     

FISH studies of the sperm of fathers of paternally derived cases of trisomy 21: no evidence for an increase in aneuploidy

Paternal nondisjunction accounts for approximately 5% of cases of trisomy 21. To test the hypothesis that, in some such cases, the fathers might be predisposed to meiotic nondisjunction, we utilized fluorescence in situ hybridization (FISH) to screen for aneuploidy in sperm. We analyzed sperm samples from ten males with a trisomy 21 offspring of paternal origin. Among these individuals, the overall frequency of disomy 21 was 0.15%, comparable to estimates of disomy 21 in the general male population. Furthermore, none of the ten fathers of trisomy 21 individuals had significantly elevated levels of disomic sperm. Thus, our results provide no evidence that the occurrence of a trisomy 21 conceptus of paternal origin imparts an increased risk of trisomy in subsequent pregnancies. Received: 9 September 1998 / Accepted: 30 September 1998     

46,XX,t(15;21)/47,XX,15p-,+21 mosaicism in a child with Down's syndrome

We report here the first case of a mosaic Down's syndrome in which both clones are trisomic for chromosome 21, one of them (90%) by a Robertsonian translocation (15;21) appearing de novo, and the other (10%) by an additional chromosome 21. Three hypotheses can explain the appearance of such a mosaic: that of a chimera formed by the fusion of two trisomy 21 zygotes, one of which had a Robertsonian translocation, the other an additional trisomy 21 zygote; that of a fusion between a chromosome 15 and a chromosome 21 in one of the early segmentation blastomeres of a trisomy 21 zygote; the more probable hypothesis of the occurrence of a fission at the break-attachment point of a Robertsonian translocation (15;21) in one of the cells arising from the early postzygotic divisions of a zygote which was a trisomy 21 by Robertsonian translocation (15;21).     

Trisomy of chromosome No. 10 in mosaic (author's transl)

A case of trisomy of chromosome No. 10 in mosaic is described in a boy who died at the age of 6 months. The frequency of pathological cells is less than 30% (28% from lymphocytes, 20% from fibroblasts); it is possible, anyway, to rule out the hypothesis of a cellular cloning in vitro, since the trisomy 10 was observed in two different cultures, terminated after 48 and 72 hours. The parents' karyotype was normal, except for a litte number (6%) of cells with trisomy 10 from cultured lymphocytes of the mother. The morphological features of the present case are compared with those of the boy described by Higurashi et al. in 1969 (mosaic of trisomy 10, with a higher frequency of pathological cells).     

Maternal serum alpha-fetoprotein screening: report of a Canadian pilot project.

A pilot project of maternal serum alpha-fetoprotein (MSAFP) screening was carried out in Ontario from 1982 to 1985 to examine the feasibility and acceptability of screening a prenatal population for open fetal neural tube defects. A total of 8140 patients at low genetic risk were screened. Patient acceptance was excellent. Blood samples were taken at 16 to 18 weeks'' gestation. If the MSAFP level was elevated, the assay was repeated and an ultrasound examination performed. Amniocentesis was offered to 67 women with unexplained persistently elevated levels. The outcome of pregnancy was known in 7473 patients (91.8%). Seven of nine known open fetal neural tube defects were detected. All were confirmed, and no unaffected fetuses were aborted on the basis of the screening results. The rates of perinatal death (6.7%), intrauterine growth retardation (11.7%) and prematurity (23.3%) were significantly higher among the patients with unexplained elevated MSAFP levels than among those with normal levels (p less than 0.001). Of 20 patients with unexplained low levels, 10 subsequently had spontaneous abortions and 10 gave birth to term appropriate-for-gestational-age infants. Seven of nine patients who gave birth to infants with autosomal trisomy had MSAFP values below the median. The findings indicate that MSAFP screening is feasible, accurate and acceptable in a low-risk area.     

Parental origin of the extra chromosome in Down's syndrome

Summary Chromosome 21 fluorescent heteromorphisms were studied in 42 patients with Down's syndrome, their parents and their siblings. Included in this number are two instances of an aunt and niece affected with trisomy 21, and one of affected siblings. One case has a de novo 21/21 translocation. Blood group, red cell and serum protein markers were also studied for linkage, gene exclusions, associations, and paternity testing. Thirty-one of the trisomy 21 cases were informative for parental origin of the extra chromosome and for stage of meiosis. The non-disjunctional event was of maternal origin in 24; 23 occurred in meiosis I, 1 in meiosis II. Seven were of paternal origin; 5 in meiosis I, and 2 in meiosis II. The translocation case was of paternal origin. A literature search revealed a total of 98 cases informative for the parent of origin of the extra chromosome, of >347 families tested. In addition, 3 de novo translocation cases, of 7 tested, were informative. The data suggest that most cases result from an error in the first meiotic division in the mother, but that a significant proportion are paternal in origin.     

Thyroid function and trisomy 21. TSH increase and rT3 deficiency

An excess of thyrotropin (TSH) with normal levels of tetraiodothyronine (T4) and of 3,5,3'-triiodothyronine (T3) was confirmed in the serum of 78 trisomy 21 children. A severe deficiency of 3,3',5'-triiodo-thyronine (rT3 or reverse T3) was observed and the decrease of the rT3/TSH ratio was highly significant. These new facts suggest that the rT3 deficiency plays a peculiar role in trisomy 21 (maybe through the regulation of one or few steps of monocarbons' metabolism). A systematic control of thyroid function (including the patient's rT3 level) is mandatory for the follow-up of every trisomy 21 patient.