Isolated Upward Rotation of the Fetal Cerebellar Vermis (Blake's Pouch Cyst) Is a Normal Variant: An Analysis of 111 Cases.

INTRODUCTION: The objective of the study was to provide more detailed data about fetal isolated upward rotation of the cerebellar vermis rotation (Blake's pouch cyst) in particular regarding pregnancy outcome. METHODS: This is a retrospective study of all cases of fetal isolated upward rotation of the cerebellar vermis (URCV) diagnosed in 3 referral centers in Italy from January 2009 to November 2019. Whenever possible, prenatal magnetic resonance imaging (MRI) was performed and a fetal karyotype was obtained. A detailed follow-up was obtained by consultation of medical records, interview with the parents, and the pediatricians. RESULTS: Our study population included 111 patients with a prenatal diagnosis of isolated URCV made at a median gestational age of 21 weeks +3 days (interquartile range (IQR) 21 + 0-22 + 2). The median brain stem-vermis (BV) angle was 27° (IQR 24-29°). In 37.9% of the cases, a regression of the finding with restoration of normal anatomy was noted at a follow-up scan or at postnatal checks. A BV angle of 25° or less predicted regression with a probability in excess of 90%. MRI was performed in utero or at birth in 101 patients and always confirmed sonographic diagnosis. Fetal CGH array and/or karyotype was available in 97 cases and was always normal, but in 1 case. A postnatal follow-up was available in 102 infants (mean 7 months, range 0-10 years of age) and documented a normal neurologic development in all the cases. CONCLUSIONS: Isolated URCV is most likely a normal variant of fetal anatomy without clinical consequences, at least at an early follow-up. A BV angle of 25° or less predicts intrauterine regression of the finding, but the outcome is good in all the cases. When a confident sonographic diagnosis is made, MRI is not mandatory. The risk of a chromosomal anomaly in these cases is probably low.

Risk of Fetal Loss in Pregnancies Undergoing Midtrimester Amniocentesis after Inconclusive Chorionic Villus Sampling.

OBJECTIVE: To estimate the procedure-related risk of miscarriage in pregnancies undergoing amniocentesis (AC) following inconclusive results for a chorionic villus sampling (CVS). METHODS: This was a multicentric retrospective cohort study of patients in which both CVS at 11-13 weeks' gestation and AC at 16-22 weeks were performed between January 1st, 2008, and July 31st, 2017. The primary outcome measure was pregnancy loss prior to 24 weeks gestation; the secondary one was intrauterine demise after 24 weeks. RESULTS: A total of 287 patients underwent transabdominal CVS and AC. Nine patients were lost at follow-up; therefore, the analysis was conducted on a population of 278 patients (275 singletons and 3 dichorionic twin pregnancies). AC was performed because of placental mosaicism (93.6%), failure of direct/semidirect preparation of trophoblastic cells (3.2%), or targeted genetic testing after the diagnosis of an anomaly in the second trimester (3.2%). In continuing pregnancies, there were no fetal losses prior to 24 weeks' gestation. Two intrauterine demises (including 1 fetus with multiple anomalies and growth restriction) in the third trimester were recorded. CONCLUSION: Patients undergoing midtrimester AC because of an inconclusive result of CVS can be reasonably reassured that in general the risk of miscarriage and fetal loss following the procedure is very small.

Interpreting mosaicism in chorionic villi: results of a monocentric series of 1001 mosaics in chorionic villi with follow-up amniocentesis.

OBJECTIVES: Chromosomal mosaicism in chorionic villi (CV) is detected in ~1-2% of cases. When a mosaic in CV is detected during prenatal diagnosis, a confirmatory karyotype should be performed on amniocytes to discriminate between a mosaic confined to the placenta [confined placental mosaicism (CPM)] and one generalized to the fetus [true fetal mosaicism (TFM)]. We determined the likelihood that any mosaic abnormalities identified through CV samples are confirmed in the fetus. METHODS: Over a period of 14 years, the laboratory analyzed both the cytotrophoblast and the mesenchyme of 60 347 CV samples. Cytogenetic results from CV samples showing mosaicism with follow-up amniocentesis were considered. The incidence of CPM and TFM and the risk of confirmation in the amniotic fluid (AF) were calculated. Uniparental disomy (UPD) was tested on ~300 cases at risk due to involvement of an imprinted chromosome. RESULTS: Overall, 1317 mosaic CV cases (2.18%) were detected, of which 1001 were subsequently investigated by amniocentesis. The overall risk of TFM was 13% and UPD incidence was 2.1%. CONCLUSIONS: The very large presented sample set and consistency in cytogenetic methodology, especially the analysis of both placental layers performed on all CV samples will enable genetic counselors to determine the risk of fetal involvement and the clinical relevance of an identified mosaic condition.

The type of feto-placental aneuploidy detected by cfDNA testing may influence the choice of confirmatory diagnostic procedure.

OBJECTIVES: Cell-free DNA (cfDNA) screening can provide false positive/negative results because the fetal fraction originates primarily from trophoblast. Consequently, invasive diagnostic testing is recommended to confirm a high-risk result. Currently, there is debate about the most appropriate invasive method. We sought to estimate the frequency in which a chorionic villus sampling (CVS) performed after a high-risk cfDNA result would require a follow-up amniocentesis due to placental mosaicism. METHODS: Analyses of the frequencies of the different types of mosaicism involving cytotrophoblasts, for trisomies 21 (T21), 18 (T18), 13 (T13) and monosomy X (MX) among 52,673 CVS karyotypes obtained from cytotrophoblast, mesenchyme and confirmatory amniocentesis. RESULTS: After a high-risk cfDNA result for T21, 18, 13 and MX, the likelihood of finding CVS mosaicism and need for amniocentesis is, respectively, 2%, 4%, 22% and 59%. When mosaicism is detected by CVS, the likelihood of fetal confirmation by amniocentesis is, respectively, 44%, 14%, 4% and 26%. CONCLUSIONS: In cases of high-risk cfDNA results for T21/T18, CVS (combining cytotrophoblast and mesenchyme analysis) can be considered, but with the caveat of 2-4% risk of an inconclusive result requiring further testing. In high-risk results for MX/T13, amniocentesis would appear to be the most appropriate follow-up diagnostic test, especially in the absence of sonographic findings.

Cytogenetic follow-up of chromosomal mosaicism detected in first-trimester prenatal diagnosis.

OBJECTIVE: To contribute to the risk assessment of true fetal mosaicism after detection of a mosaic chromosomal anomaly in chorionic villus samples (CVS) in order to enable more effective counseling and pregnancy management. METHODS: We retrospectively reviewed 7112 consecutive CVS analyzed on both direct preparations and cultured cells. In 135 out of the 177 cases of mosaicism, we performed cytogenetic follow-up and determined the frequency of confined placental mosaicism (CPM) and true fetal mosaicism according to type and distribution of the cytogenetic abnormality. RESULTS: True fetal mosaicism was detected in 38 out of 135 cases (28.15%), confirming the higher incidence of CPM (71.85%). Confirmation rate of CV mosaicism depends on the combination of placental cell lineages affected, chromosome involved and mosaic versus non-mosaic chromosomal anomaly. The overall probability of fetal involvement significantly rises with involvement of mesenchymal cells: 5.88% abnormal cytotrophoblast, 20.96% abnormal mesenchyme and 58.97% anomalies in both tissues. CONCLUSION: Most of the mosaic findings at CVS are unreliable indicators of the fetal karyotype. Our study contributes to large series with cytogenetic information from the different tissues along the cytotrophoblast-extraembrional mesoderm-fetus axis in order to infer clinical relevance of the findings and to enable more effective genetic counseling.

Structural chromosomal abnormalities detected during CVS analysis and their role in the prenatal ascertainment of cryptic subtelomeric rearrangements.

Mosaic structural chromosomal abnormalities observed along the trophoblast-mesenchyme-fetal axis, although rare, pose a difficult problem for their prognostic interpretation in prenatal diagnosis. Additional issues are raised by the presence of mosaic imbalances of the same chromosome showing different sizes in the different tissues, that is, deletions and duplications in the cytotrophoblast and mesenchyme of chorionic villi (CV). Some of these cytogenetic rearrangements originate from the post-zygotic breakage of a dicentric chromosome or of the product of its first anaphasic breakage. Selection of the most viable cell line may result in confined placental mosaicism of the most severe imbalance, favoring the presence of the cell lines with the mildest duplications or deletions in the fetal tissues. We document three cases of ambiguous results in CV analysis due to the presence of different cell lines involving structural rearrangements of the same chromosome which were represented differently in the trophoblast and the mesenchyme. Observation by conventional karyotype of a grossly rearranged chromosome in one of the CV preparations (direct or culture) was crucial to call attention to the involved chromosomal region in other tissues (villi or amniotic fluid), allowing the prenatal diagnosis through molecular cytogenetic methods of subtelomeric rearrangements [del(7)(q36qter); del(11)(q25qter); del(20)(p13pter)]. This would have surely been undiagnosed with the routine banding technique. In conclusion, the possibility to diagnose complex abnormalities leading to cryptic subtelomeric rearrangements, together with a better knowledge of the initial/intermediate products leading to the final abnormal cryptic deletion should be added to the advantages of the CV sampling technique.

Persistence of a monosomic cell line in a fetus with mosaic trisomy 8.

We report on a fetus presenting with an increased nuchal translucency, in which chorionic villus sampling led to the diagnosis of mosaic trisomy 8. Ultrasound scan performed at 15(+6) weeks revealed bilateral cleft lip and palate, flat facial profile, and arrhinia. Pregnancy was terminated at 16(+6); postmortem examination showed additional findings including hypospadias, bilateral renal dysplasia, and focal portal fibrosis of the liver. In order to confirm the presence of trisomy 8, FISH analysis was performed in abnormal renal and hepatic tissue, which, unexpectedly, showed a higher fraction of cells with only one fluorescent probe signal (43% and 23%, respectively), if compared with normal fetal liver and kidney (3-10%). This finding is consistent with the survival in this fetus of a monosomic cell line after mitotic non-disjunction, which is in contrast with what is generally thought about mosaic trisomy genesis. We hypothesize that the possible persistence of the monosomic cell line, in addition to the variable distribution of aneuploid cells in the body tissues, could explain the high heterogeneity of mosaic trisomy 8 phenotype.

Attitudes of women of advanced maternal age undergoing invasive prenatal diagnosis and the impact of genetic counselling.

Despite the increasing availability and effectiveness of non-invasive screening for foetal aneuploidies, most women of advanced maternal age (AMA) still opt for invasive tests. A retrospective cross-sectional survey was performed on women of AMA undergoing prenatal invasive procedures, in order to explore their motivations and the outcome of preliminary genetic counselling according to the approach (individual or group) adopted. Of 687 eligible women, 221 (32.2%) participated: 117 had received individual counselling, while 104 had attended group sessions. The two groups did not differ by socio-demographic features. The commonest reported reason to undergo invasive tests was AMA itself (67.4%), while only 10.4% of women mentioned the opportunity of making informed choices. The majority perceived as clear and helpful the information received at counselling, and only 12.7% had doubts left that, however, often concerned non-pertinent issues. The impact of counselling on risk perception and decisions was limited: a minority stated their perceived risk of foetal abnormalities had either increased (6.8%) or reduced (3.6%), and only one eventually declined invasive test. The 52.6% of women expressed a preference toward individual counselling, which also had a stronger impact on perceived risk reduction (P=0.003). Nevertheless, group counselling had a more favourable impact on both clarity of understanding and helpfulness (P=0.0497 and P=0.035, respectively). The idea that AMA represents an absolute indication for invasive tests appears deeply rooted; promotion of non-invasive techniques may require extensive educational efforts targeted to both the general population and health professionals.

Prenatal diagnosis versus first-trimester screening of trisomy 21 among pregnant women aged 35 or more.

OBJECTIVE: To compare the policy of prenatal diagnosis versus first trimester screening of trisomy 21 among pregnant women of advanced age. METHODS: A retrospective study was conducted on patients aged ≥35 divided in two groups: patients who requested first trimester combined test and only in case of screen-positive result underwent invasive testing (group A); patients undergoing chorionic villous sampling or amniocentesis as first investigation (group B). The following outcome variables were compared: antenatal detection of trisomy 21, occurrence of trisomy 21 at birth, miscarriage rate, hospitals' costs. RESULTS: 4527 women were included. Of these, 534 (11.80%) underwent T21 screening whereas 3993 (88.20%) requested primary invasive testing. In group A, 64 combined test were positive (11.99%) and 8 trisomy 21 cases were diagnosed (1.50%); the loss of euploid fetuses after invasive procedure was 4.55% (2/44). No false-negative case was observed. In group B 57 cases of trisomy 21 were diagnosed (1.43%), and pregnancy loss rate of chromosomally normal fetuses was 0.45% (17/3806). The estimated cost was, respectively, 67.720€ for the primary screening versus 1.996.500€ for direct prenatal diagnosis. CONCLUSION: First trimester screening of trisomy 21 is highly accurate and cost saving among women ≥35.

Prenatal phenotype of Williams-Beuren syndrome and of the reciprocal duplication syndrome.

KEY CLINICAL MESSAGE: Copy losses/gains of the Williams-Beuren syndrome (WBS) region cause neurodevelopmental disorders with variable expressivity. The WBS prenatal diagnosis cannot be easily performed by ultrasound because only few phenotypic features can be assessed. Three WBS and the first reciprocal duplication prenatal cases are described with a review of the literature.

Complex rearrangement of the exon 6 genomic region among Opitz G/BBB Syndrome MID1 alterations.

Opitz G/BBB Syndrome (OS) is a multiple congenital anomaly disorder characterized by developmental defects of midline structures. The most relevant clinical signs are ocular hypertelorism, hypospadias, cleft lip and palate, laryngo-tracheo-esophageal abnormalities, imperforate anus, and cardiac defects. Developmental delay, intellectual disability and brain abnormalities are also present. The X-linked form of this disorder is caused by mutations in the MID1 gene coding for a member of the tripartite motif family of E3 ubiquitin ligases. Here, we describe 12 novel patients that carry MID1 mutations emphasizing that laryngo-tracheo-esophageal defects are very common in OS patients and, together with hypertelorism and hypospadias, are the most frequent findings among the full spectrum of OS clinical manifestations. Besides missense and nonsense mutations, small insertions and deletions scattered along the entire length of the gene, we found that a consistent number of MID1 alterations are represented by the deletion of single coding exons. Deep characterization of one of these deletions reveals, for the first time within the MID1 gene, a complex rearrangement composed of two deletions, an inversion and a small insertion that may suggest the involvement of concurrent non-homologous mechanisms in the generation of the observed structural variant.