Complex mosaic blastocysts after preimplantation genetic testing: prevalence and outcomes after re-biopsy and re-vitrification.

RESEARCH QUESTION: What is the incidence of complex mosaic in preimplantation genetic testing (PGT) blastocysts and can it be managed in clinical practice? DESIGN: A retrospective study of PGT cycles conducted between January 2018 and October 2019 at a single centre. Biopsies of blastocysts were collected and analysed by next-generation sequencing (NGS). Complex mosaic blastocysts were defined as those with three or more mosaic chromosomes. The cryopreserved complex mosaic blastocysts underwent a second round of biopsy, NGS analysis and vitrification. The euploid blastocysts identified by the re-biopsy were warmed again for embryo transfer. The main outcomes included the prevalence of the complex mosaic and the ongoing pregnancy rate. RESULTS: The prevalence of the complex mosaic was 2.4% (437/17,979). The prevalence of the complex mosaic was not associated with maternal age and morphological quality. A total of 89 complex mosaic blastocysts underwent re-biopsy and 96.6% (86/89) survived the first warming. For the re-biopsy samples, 61.6% (53/86) were euploid. The poor-quality blastocysts had higher rates of aneuploidy compared with good-quality blastocysts. The survival rate for blastocysts undergoing the second warming was 100% (18/18) and resulted in an ongoing pregnancy rate of 38.9% (7/18) as well as the birth of six healthy infants. CONCLUSION: Re-biopsy may rescue blastocysts with development potential for transfer and improve the cumulative pregnancy rate per stimulation cycle in patients containing complex mosaic blastocysts.

Whether to transfer mosaic embryos: a cytogenetic view of true mosaicism by amniocentesis.

RESEARCH QUESTION: Preimplantation genetic testing for aneuploidies has increasingly been employed for embryo selection, resulting in a recent surge in mosaic embryos. According to the cytogenetic results, which types of mosaic embryo survive early pregnancy, progress to the second trimester and finally result in a live birth? DESIGN: This study evaluated 30,587 pregnant women undergoing amniocentesis from January 2004 to March 2020 at the cytogenic centre of Kaohsiung Chang Gung Memorial Hospital. Samples from amniocentesis were cultured using the in-situ method. The types and distribution of level III chromosomal mosaicism (two or more cells with the same abnormality in two or more colonies and both culture dishes, clinically referred to as 'true mosaicism') were retrospectively reviewed. RESULTS: Among the 30,587 women, 78 cases (0.26%) of level III chromosomal mosaicism were identified. The types of chromosomal mosaicism were classified as sex chromosome mosaicism (SCM), autosomal chromosome mosaicism (ACM) and marker chromosome mosaicism (MCM), with SCM, ACM and MCM accounting for 58.97%, 32.05% and 8.97% of cases, respectively. The most common mosaic cell lines were monosomy X and trisomy 21. The most common mosaic cell line progressing to live birth was monosomy X. CONCLUSIONS: Mosaic monosomy X and trisomy 21 are the most common cell lines of true mosaicism determined by amniocentesis. Monosomy X mosaicism is the most common cell line in live births. For women considering the transfer of these types of mosaic embryo in a circumstance where euploid embryos are unavailable, clinicians should provide careful prenatal counselling, detailed ultrasonography and amniocentesis.

Prevalence, types and possible factors influencing mosaicism in IVF blastocysts: results from a single setting.

RESEARCH QUESTION: Are intrinsic or extrinsic factors associated with embryo mosaicism prevalence in IVF cycles? DESIGN: Retrospective cohort study of preimplantation genetic testing for aneuploidy (PGT-A) cycles carried out at a university-affiliated IVF clinic between October 2017 and October 2019. Trophectoderm biopsies were analysed by next generation sequencing. Mosaicism prevalence, type of anomaly and the chromosomes involved were analysed. Intrinsic and extrinsic factors potentially inducing mosaicism were studied: maternal and paternal age, antral follicle count, cumulus-oocyte complexes retrieved, female body mass index, PGT-A indication, sperm concentration, total dosage of gonadotrophins, embryo quality and day of blastocyst formation, single-step commercial media used and biopsy operator. RESULTS: Overall prevalence of mosaicism in our PGT-A setting was 13.9%. In segmental mosaicism, larger chromosomes tended to be more affected, which was not observed in whole-chromosome mosaicism. Additionally, segmental mosaicism was mostly observed in monosomy (69.6%; P < 0.01) compared with whole-chromosome mosaicism (49.7% monosomies versus 50.3% trisomies; P = 0.83). Although a high inter-patient variability was observed, only paternal age showed a positive association with mosaicism (adjusted OR 1.26, 95% CI 1.02 to 1.54) among the analysed variables. CONCLUSIONS: Our results suggest remarkable differences in the mechanisms generating segmental and whole-chromosome mosaicism, indicating that they may deserve different consideration when studying them and when prioritizing them for transfer. Male factor seems to be associated with mosaicism and may be worthy of specific assessment in future studies.

Impact of mosaicism ratio on positive predictive value of cfDNA screening.

OBJECTIVE: To examine the relationship between the fraction of cell-free DNA (cfDNA) affected by aneuploidy compared to the overall fetal fraction of a prenatal screening specimen and its effect on positive predictive value (PPV). METHOD: CfDNA specimens positive for trisomy 13, 18, and 21 with diagnostic outcomes were analysed over a 22-month period in one clinical laboratory. For each positive specimen, a "mosaicism ratio" (MR) was calculated by dividing the fraction of cfDNA affected by aneuploidy by the overall fetal fraction of the specimen. PPVs were calculated and analyzed based on various MR ranges. RESULTS: Trisomy 13 was the aneuploidy most commonly seen in mosaic form, followed by trisomy 18 and trisomy 21. Significant differences in positive predictive values were noted for all three trisomies between samples with an MR in the "mosaic" versus "non-mosaic" range, as well as between results classified as "low-mosaic" versus "high-mosaic." CONCLUSION: PPVs may be influenced, in part, by the mosaicism ratio associated with a particular result. The data generated from this study may be useful in providing more personalized risk assessments for patients with positive cfDNA screening results.

The outcomes after transfers of embryos with chromosomal mosaicism: a single reproductive medicine center experience at iVF Riga clinic.

Aim: The aim of this study is to summarize the outcomes of transfers of mosaic embryos, which were classified according to guidelines and in strong collaboration of reproductologists, clinical geneticists and patients approved as suitable for transfer. Material and Methods: Retrospective data were collected from 70 patients from a private IVF center to whom embryos with mosaic changes in chromosomal material were transferred from 2015 to 2019. Results and Conclusion: Implantation outcomes and continuing pregnancies showed slight differences, when compared to fully normal embryos. Artifacts have to be differentiated from undeniable aberrations, and correct interpretation of results must be done with following patient counselling and prenatal testing if necessary.

Prevalence of mosaicism in uncultured chorionic villus samples after chromosomal microarray and clinical outcome in pregnancies affected by confined placental mosaicism.

OBJECTIVE: To evaluate the prevalence of mosaicism in chorionic villus sampling (CVS) samples after chromosomal microarray (CMA) and clinical outcome of pregnancies affected by confined placental mosaicism. METHOD: We retrieved all results from CMA, array-based comparative genomic hybridization, on CVS samples from January 2011 to November 2017 from Central and North Denmark Regions. Mosaic results from uncultured chorionic villi, cytotrophoblasts and mesenchymal cells, after CVS and follow-up on amniocytes, fetal tissue, or postnatal blood were studied and matched with clinical data from The Danish Fetal Medicine Database. RESULTS: Prevalence of mosaicism was 93 out of 2,288 (4.1%) CVS samples of which 17 (18.3%) concerned submicroscopic copy number variations (CNVs) <10 Mb. Follow-up analyses were performed in 62 cases. True fetal mosaicism (TFM) was confirmed in 18.4% (7/38) when mosaicism involved whole chromosome aneuploidy and in 25.0% (6/24), when involving a CNV (P = .59). Median birth weight z-score was higher in cases of confined placental mosaicism for a CNV (0.21) than cases involving whole chromosomes (-0.74) (P = .02). CONCLUSION: Prevalence of mosaicism in CVS samples is higher after CMA on uncultured tissue than after conventional karyotyping on cultured tissue. The risk of TFM is equally high in cases of mosaicism for CNVs and whole chromosomes.

Next-generation sequencing analysis of embryos from mosaic patients undergoing in vitro fertilization and preimplantation genetic testing.

OBJECTIVE: To investigate the effects of parental mosaicism on their preimplantation embryos. DESIGN: Case series. SETTING: An institute for reproductive and stem cell engineering. PATIENT(S): Sixty-eight mosaic couples. INTERVENTION(S): Assisted reproduction with preimplantation genetic testing (PGT). MAIN OUTCOME MEASURE(S): Karyotypes, embryo-related chromosomal abnormalities, and PGT results. RESULT(S): A total of 209 embryos were obtained from 68 mosaic couples, and 153 (73.21%) of 209 of the total embryos were obtained from 55 mosaic couples with abnormal sex chromosome numbers. Of these 153 embryos, 2 (1.31%) had an abnormal copy number of X chromosome, 1 had mosaicism with 46,XN,+X(mosaic, 40%), 1 (0.65%) had an extra Y chromosome, 3 (1.96%) exhibited both X chromosomal and autosomal abnormalities, and 4 (2.61%) exhibited de novo X chromosome structural abnormalities. A total of 56 (26.79%) of 209 embryos were obtained from mosaic couples (n = 13) with abnormal autosomal structures. Notably, of these 56 embryos, 5 (8.93%) had a 16q21-q24.3 copy number abnormality related to the parental karyotype, with a fragile site at 16q22; 5 (7.14%) exhibited 46,XX,dup(8p23.1-8p11.21) and 46,XY,del(8p22-8p11.21), which were related to the parental karyotype; and 10 (17.86%) were de novo chromosome abnormalities. CONCLUSION(S): Our data demonstrate that the risk of embryo-related chromosome abnormalities in mosaic patients with abnormal sex chromosomes is very low. Therefore, PGT may not need to be recommended for mosaic patients with abnormal copy numbers of sex chromosomes, especially for patients with financial difficulties. By contrast, the mosaic patients with structural abnormalities of autosomes may have a relatively high risk of abnormal embryos with an unbalanced segment of the involved chromosomes. Thus, PGT is highly recommended for mosaic patients with autosomal structure abnormalities, especially those with a fragile site at 16q22.

Population-based trends in the prenatal diagnosis of sex chromosome aneuploidy before and after non-invasive prenatal testing.

OBJECTIVE: To assess the impact of non-invasive prenatal testing (NIPT) on trends in the prenatal diagnosis of sex chromosome aneuploidy (SCA) in a population with >73,000 annual births. METHOD: Retrospective population-based cohort study from 1986-2016 of all women undergoing prenatal diagnosis before 25 weeks gestation in the Australian state of Victoria. Statistical significance was tested using the chi-square test for trend or proportions. RESULTS: There were 2,043,345 births and 842 SCA diagnoses from 1986-2016. The percentage of prenatal diagnostic tests leading to a SCA diagnosis increased significantly from 0.95% in 2010 to 2.93% in 2016 (p < 0.001) but due to a concurrent decline in testing, the annual prenatal diagnosis rate of SCA remained stable at 4.4/10,000 births. Among confirmed fetal SCAs the most common indication for testing in 1986 was advanced maternal age (63%); in 2016 it was high risk NIPT (49%). CONCLUSION: SCAs now make up an increasing proportion of prenatal diagnostic results but due to the overall decline in diagnostic testing, the prenatal prevalence as a percentage of births remained steady. The ascertainment of fetal SCA has evolved from an incidental finding after testing for increased risk of trisomy 21, to a diagnosis obtained after suspected SCA on NIPT.

Higher male prevalence of chromosomal mosaicism detected by amniocentesis.

OBJECTIVE: To present the calculated frequencies, male to female sex-ratio, and modes of ascertainments in different levels of chromosomal mosaicism (CM) detected at amniocentesis. MATERIALS AND METHODS: This's a 10-years retrospective study between January 2008 and December 2017 and there were 13,752 cases of amniocentesis performed in MacKay Memorial Hospital, Taipei, Taiwan. Eight hundred and thirty four cases of CM were collected in this study. We reviewed their types of chromosomal abnormalities of mosaicism, the modes of ascertainment (including: advanced maternal age, abnormal ultrasound findings, abnormal maternal serum screening result, and other reasons), maternal age, gestational age at amniocentesis, fetal gender, and perinatal findings. After amniocentesis, in situ culture was performed and the results of karyotype with CM were divided in to three levels. RESULTS: In our sample of 13,752 amniocentesis, 834 cases with all levels of CM were collected in this study. Of them, there were 562 cases (4.09%) with level I mosaicism, 207 cases (1.51%) of level II mosaicism, and 65 cases (0.47%) of level III mosaicism (Table 1). In the group of advanced of maternal age (AMA), their calculated frequencies, 4.18% in level I, 1.46% in level II and 0.41% in level III, were very similar to those in total cases (p value = 0.206) without statistical significance. In the group of abnormal ultrasound findings, the calculated frequency was much higher in level III (0.87%), however, there was no statistical significance because of the small numbers of level III. In our cases of amniocentesis, the case numbers of male case (50.20%) is very similar to female (49.80%), and the male to female ratio was 1.01. But, we found more cases of male with CM (444 cases) than female (390 cases). The sex-ratio in different levels' calculated frequencies of CM showed similar in level I, and male prevalence was found in level II and III with statistical significance (p value = 0.022). The male prevalence also revealed in both numerical and structural abnormalities in level II and level III, but no difference in the cases of level I. CONCLUSION: In conclusion, our observation showed a novel finding of higher male prevalence of CM in level II and III, and both in numerical and structural abnormalities. It's consistent with the theory of better survival in male embryo after partial self-correction of initial chromosomal aberrations, male-specific selection against chromosomal abnormalities.

Outdoor air pollution and mosaic loss of chromosome Y in older men from the Cardiovascular Health Study.

BACKGROUND: Mosaic loss of chromosome Y (mLOY) can occur in a fraction of cells as men age, which is potentially linked to increased mortality risk. Smoking is related to mLOY; however, the contribution of air pollution is unclear. OBJECTIVE: We investigated whether exposure to outdoor air pollution, age, and smoking were associated with mLOY. METHODS: We analyzed baseline (1989-1993) blood samples from 933 men ≥65 years of age from the prospective Cardiovascular Health Study. Particulate matter ≤10 µm (PM10), carbon monoxide, nitrogen dioxide, sulfur dioxide, and ozone data were obtained from the U.S. EPA Aerometric Information Retrieval System for the year prior to baseline. Inverse-distance weighted air monitor data were used to estimate each participants' monthly residential exposure. mLOY was detected with standard methods using signal intensity (median log-R ratio (mLRR)) of the male-specific chromosome Y regions from Illumina array data. Linear regression models were used to evaluate relations between mean exposure in the prior year, age, smoking and continuous mLRR. RESULTS: Increased PM10 was associated with mLOY, namely decreased mLRR (p-trend = 0.03). Compared with the lowest tertile (≤28.5 µg/m3), the middle (28.5-31.0 µg/m3; ß = -0.0044, p = 0.09) and highest (≥31 µg/m3; ß = -0.0054, p = 0.04) tertiles had decreased mLRR, adjusted for age, clinic, race/cohort, smoking status and pack-years. Additionally, increasing age (ß = -0.00035, p = 0.06) and smoking pack-years (ß = -0.00011, p = 1.4E-3) were associated with decreased mLRR, adjusted for each other and race/cohort. No significant associations were found for other pollutants. CONCLUSIONS: PM10 may increase leukocyte mLOY, a marker of genomic instability. The sample size was modest and replication is warranted.

Rare X Chromosome Abnormalities in Systemic Lupus Erythematosus and Sjögren's Syndrome.

OBJECTIVE: Sjögren's syndrome (SS) and systemic lupus erythematosus (SLE) are related by clinical and serologic manifestations as well as genetic risks. Both diseases are more commonly found in women than in men, at a ratio of ~10 to 1. Common X chromosome aneuploidies, 47,XXY and 47,XXX, are enriched among men and women, respectively, in either disease, suggesting a dose effect on the X chromosome. METHODS: We examined cohorts of SS and SLE patients by constructing intensity plots of X chromosome single-nucleotide polymorphism alleles, along with determining the karyotype of selected patients. RESULTS: Among ~2,500 women with SLE, we found 3 patients with a triple mosaic, consisting of 45,X/46,XX/47,XXX. Among ~2,100 women with SS, 1 patient had 45,X/46,XX/47,XXX, with a triplication of the distal p arm of the X chromosome in the 47,XXX cells. Neither the triple mosaic nor the partial triplication was found among the controls. In another SS cohort, we found a mother/daughter pair with partial triplication of this same region of the X chromosome. The triple mosaic occurs in ~1 in 25,000-50,000 live female births, while partial triplications are even rarer. CONCLUSION: Very rare X chromosome abnormalities are present among patients with either SS or SLE and may inform the location of a gene(s) that mediates an X dose effect, as well as critical cell types in which such an effect is operative.

Association of Parental Age and the Type of Down Syndrome on the Territory of Bosnia and Herzegovina.

BACKGROUND: Advanced paternal and/or maternal age is a classic risk factor for Down syndrome. The aim of the study was to investigate the frequency of Down syndrome types in children and its association with maternal and paternal age in Bosnia and Herzegovina. SUBJECTS AND METHODS: The cross sectional, observational study included 127 children, 49 girls and 78 boys, aged 1-180 months suspected to have Down syndrome, admitted to the Centre for Genetics, Faculty of Medicine University of Sarajevo, for cytogenetic analysis and differential diagnosis of Down syndrome during the period from January 2010 to May 2015. Standard method of 72 hours cultivation of peripheral blood lymphocytes has been applied. The accepted level of statistical significance was p<0.05. STUDY RESULTS: The most common type of Down syndrome was standard trisomy (86.6%), comparing to translocation and mosaicism (7.1%; 6.3%, respectively). The highest frequency of Down syndrome cases was in mother and father's group from 30-39 years old (57; 57 children, respectively) compared to mother and father's groups with younger than 30 (44; 29, respectively) and 40 and older (26; 41, respectively). The significant difference was found in maternal age between translocation and mosaicism groups (p=0.036). Difference between parental years and type of Down syndrome was significant when Standard trisomy 21 and translocation (p=0.045), as well as mosaicism and translocation (p=0.036), were compared. CONCLUSION: The most common type of Down syndrome was standard trisomy 21, with highest occurrence in parents from 30 to 39 years old. Parents were the youngest in translocation group. Obtained results suggest that multidisciplinary approach to identifying the trigger for trisomy appearance and the influence of maternal age is required.

Postnatal Identification of Trisomy 21: An Overview of 7,133 Postnatal Trisomy 21 Cases Identified in a Diagnostic Reference Laboratory in China.

This study describes the cytogenetic characteristics of 7,133 trisomy 21 (Tri21) identified from 247,818 consecutive postnatal cases karyotyped in a single reference laboratory in China for a period of 4 years. The average detection rate of Tri21 is 2.88% ranging from 3.39% in 2011 to 2.52% in 2014. The decreased detection rates over the years might reflect a possible impact of noninvasive prenatal testing applied rapidly in China and elective termination of affected pregnancies. 95.32% of the Tri21 karyotypes are standard Tri21, 4.53% are Robertsonian Tri21, and less than 1% are other Tri21 forms. There are more mosaic Tri21 in older children and adults, consistent with previous observations that clinical features in individuals with mosaic Tri21 are generally milder and easily missed during perinatal period. The male/female (M/F ratio) for the total 7,133 Tri21 cases and for the 6,671 cases with non-mosaic standard Tri21 are 1.50 and 1.53 respectively, significantly higher than the 0.93 for all the 247,818 cases we karyotyped, the 1.30 for the Down syndrome (DS) identified during perinatal period in China, and the 1.20 for the livebirth in Chinese population. In contrast, the mosaic standard Tri21 case has a significantly lower proportion of males when compared with the non-mosaic standard Tri21, indicating different underlying mechanisms leading to their formations. Opposite M/F ratios in different subtypes of ROB Tri21 were observed. A long list of rare or private karyotypes where Tri21 are concurrently present was identified. The large collection of Tri21 cases with a diversity of clinical findings and a wide age range allowed us to determine the frequency of the different karyotypes of Down syndrome in China, given the fact that this kind of national epidemiological data is lacking currently.

Chromosomal deletions detected at amniocentesis.

OBJECTIVE: The aim of this study is to present the incidence, prenatal and postnatal findings, and modes of ascertainment in chromosomal deletions detected at amniocentesis. MATERIALS AND METHODS: We reviewed all the cases with chromosomal deletions, which were detected by amniocentesis in Mackay Memorial Hospital, Taipei, Taiwan, between January 1987 and December 2012. Data on the locations and types of deletion, reasons for performing amniocentesis, maternal age, gestational age at amniocentesis, fetal karyotypes, inheritance of deletions, and relative prenatal findings were collected. RESULTS: Amniocentesis was performed in 33,305 cases within this period of time. Among these, 31 cases of chromosomal deletions were considered for the study. The mean gestational age at amniocentesis was 21.0 weeks (range from 15 weeks to 32 weeks) and the mean maternal age at amniocentesis was 32.1 years (range from 26 years to 37 years). Nineteen cases (61.3%) manifested fetal structural abnormalities on ultrasound, nine (29.0%) presented no ultrasound abnormalities, and three had an unknown status. The main modes of ascertainment included abnormal ultrasound findings in 10 cases (32.2%), advanced maternal age in 11 cases (35.5%), abnormal maternal serum screening results in six cases (19.6%), and other reasons in four cases (13.0%). Of the 27 cases with known inheritance, the deletion was inherited in two (6.6%) and de novo in 25 (92.6%). Males accounted for 11 (35.5%) and females for 20 (64.5%) cases. Chromosomal deletions are more often to occur in chromosomal 5(4 cases, 12.9%), chromosomal 18 (4 cases, 12.9%), chromosomal 4 (3 cases, 9.7%), chromosomal 7 (3 cases, 9.7%), chromosomal 10 (3 cases, 9.7%), chromosomal 11 (3 cases, 9.7%), and chromosomal 1 (2 cases, 6.5%). There were four cases of chromosomal mosaicism: two involved chromosome 5, one involved chromosome 10, and one involved chromosome 18. Twenty-three cases (74.2%) had terminal deletions and the other eight cases (26.7%) had interstitial-type deletions. CONCLUSION: In summary, we have presented the results of prenatal diagnosis for chromosomal deletions using amniocentesis. Chromosomal deletions are more likely to occur in females and more often in chromosomal 5p and 18q. Prenatal diagnosis at amniocentesis is frequently associated with advanced maternal age, abnormal ultrasound findings, and abnormal maternal serum screening. The frequency of ascertainment in chromosome deletion seems to be directly correlated with advanced maternal age and abnormal ultrasound findings. In cases with terminal deletions, prenatal ultrasound plays a more important role for prenatal diagnosis.

Phenotypic differences in mosaic Klinefelter patients as compared with non-mosaic Klinefelter patients.

OBJECTIVE: To determine whether men with Klinefelter syndrome (KS) have the same phenotype as men with mosaic KS. DESIGN: Subject identification via prospectively collected database. SETTING: Male infertility specialty clinic. PATIENT(S): Men undergoing a fertility evaluation from 2005 to 2012 at a single male infertility specialty clinic and having a karyotype demonstrating KS (mosaic or non-mosaic). INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Testicular size, and semen and hormone parameters, genetic evaluation, and signs of testosterone (T) deficiency using validated questionnaires. RESULT(S): Of 86 men identified with KS, 6 (6.7%) were mosaic KS, and 80 (93.3%) were non-mosaic KS. Men with mosaic KS had lower baseline luteinizing hormone (LH) levels (10.31 IU/L ± 5.52 vs. 19.89 IU/L ± 6.93), lower estradiol levels (58.71 ± 31.10 pmol/L vs. 108.57 ± 43.45 pmol/L), larger mean testicular volumes (11 ± 7.3 mL vs. 6.35 ± 3.69 mL), and a higher mean total sperm count (4.43 ± 9.86 M/mL vs. 0.18 ± 1.17 M/mL). A higher proportion of men with mosaic KS had sperm in the ejaculate: 3 (50%) of 6 versus 3 (3.75%) of 80. The Sexual Health Inventory for Men (SHIM) and Androgen Deficiency in the Aging Male (ADAM) questionnaire scores were not different between groups. CONCLUSION(S): Men with mosaic KS seem to be more well androgenized than their non-mosaic KS counterparts, both with respect to hormones and sperm in the ejaculate.

De novo small supernumerary marker chromosomes detected on 143,000 consecutive prenatal diagnoses: chromosomal distribution, frequencies, and characterization combining molecular cytogenetics approaches.

OBJECTIVE: The risk of clinical consequences in prenatal cases with de novo small supernumerary marker chromosomes (sSMC), often in mosaic conditions, is not easy to predict, which results in difficulties in genetic counseling. METHOD: In this study, we evaluated the frequency, the chromosomal origin, and the clinical indication of 104 de novo sSMC detected in a monocenter survey on the basis of 143,000 consecutive prenatal diagnoses, and we assessed the reliability of molecular cytogenetics technologies for sSMC characterization. RESULTS: We detected a de novo sSMC frequency of 0.072%. Its incidence in advanced maternal age group is statistically different from that found in maternal anxiety indication (<35 years old). A higher prevalence of mosaicism in chorionic villi sampling (CVS) than in amniotic fluids was also revealed related to confined placental mosaicisms. The risk of confirmation in amniotic fluids of mosaics previously revealed at CVS was 33.3%. No uniparental disomy conditions were found when imprinted chromosomes were involved in the occurrence of de novo sSMC. The majority of de novo sSMC were acrocentric derived-chromosomes, and a neocentromere formation was observed in one pregnancy. CONCLUSION: Our data support that array comparative genomic hybridization has improved sSMC characterization and demonstrate its utility in supporting genetic counseling. We propose a workflow for de novo sSMC characterization.

Mosaicos cromosómicos en vellosidad corial / Chromosomal mosaicism in chorionic villi

Introducción. El estudio de vellosidades coriales comprende realizar 2 cultivos celulares que pueden no tener resultados coincidentes. Estas discrepancias pueden ser debidas a mosaicos citogenéticos de origen in vivo o in vitro. En este trabajo nos planteamos analizar los cariotipos en mosaicos, ligado con los rendimientos de los cultivos celulares y los resultados citogenéticos. Material y métodos. Se han analizado 2.360 muestras prenatales y 510 de vellosidades de abortos. Con las muestras prenatales se efectúan rutinariamente 2 cultivos celulares, cultivo corto y cultivo largo, y para los abortos además se han estudiado muestras de restos fetales. Resultados. El porcentaje de muestras con resultado citogenético para el grupo prenatal fue del 99,9% y para el grupo de abortos del 87,1%. El porcentaje de anomalías cromosómicas en el grupo prenatal fue del 10,6% siendo las aneuploidías comunes (trisomías 13, 18, y 21) las más frecuentes, y para el grupo de abortos fue del 55,1% siendo las aneuploidías no-comunes las más frecuentes. El porcentaje de cariotipos en mosaico para el grupo prenatal fue del 3,1% y para el grupo de abortos del 6,8%. El mosaico confinado a la placenta tipo ii fue el más frecuente. Conclusiones. Para el estudio de los mosaicos en vellosidades coriales la mejor estrategia es realizar los 2 cultivos paralelos en muestras prenatales y los 3 cultivos en muestras de abortos. Teniendo en cuenta el riesgo que asume la pareja ante una prueba invasiva, es nuestro deber dar el resultado citogenético más completo posible(AU)

Introduction. The study of chorionic villus samples comprises performing two cell cultures that may not have matching results. These discrepancies may be due to cytogenetic mosaics of in vivo or in vitro origin. This study included analysing the karyotypes in mosaics, associated with the cell culture and cytogenetic results. Material and methods. Prospective study based on the analysis of 2,360 chorionic villus samples and 510 spontaneous abortion samples. Two cultures were routinely performed on the prenatal samples (short and long), as well as on the abortion samples. Results. The success rate was 99.9% in the prenatal group, and 87.1% in the abortion group. The percentage of chromosomal anomalies in the prenatal group was 10.6%, with the common aneuploidies (trisomy 13, 18, and 21) being the most frequent. In the abortions group there 55.1% anomalies, with uncommon aneuploidy the most frequent. The percentage of mosaicism in the prenatal group was 3.1%, and it was 6.8% in the abortion group. The confined placental mosaicism type ii was the most frequent. Conclusions. For the study of the mosaicism in chorionic villi samples the best strategy is to perform 2 prenatal samples cultures in parallel, and 3 abortion samples cultures. Given the risk to the mother and child using this invasive test, it is our duty to give the most comprehensive cytogenetic results achievable(AU)

Diagnóstico prenatal de disomía uniparental / Prenatal diagnostic testing for uniparental disomy

La presencia en un paciente de un fenotipo clínico característico es la indicación usual para el estudio posnatal de posible disomía uniparental (DUP). En diagnóstico prenatal la situación es más compleja, ya que la información clínica es mucho más limitada, y los estudios de DUP se plantean únicamente en determinadas situaciones de riesgo, relacionadas con la presencia de alteraciones cromosómicas numéricas o estructurales en el conjunto feto/placenta o en los progenitores, o con la detección ecográfica de algún tipo de anomalías del desarrollo fetal o de malformaciones fetales. El objetivo del presente trabajo es presentar la experiencia de nuestro centro en diagnóstico prenatal de DUP. Métodos. Desde 1998 se han realizado en nuestro centro 165 estudios prenatales de DUP de los cromosomas 6 (n = 1), 7 (n = 24), 11 (n = 4), 14 (n = 81) y 15 (n = 55) correspondientes a 154 gestaciones; en 11 de ellas se han estudiado 2 cromosomas a la vez. El estudio molecular se ha realizado mediante el análisis de segregación de marcadores microsatélites polimórficos distribuidos a lo largo del cromosoma implicado. Resultados. Se han detectado 2 casos de DUP materna, uno del cromosoma 7 y otro del 15, ambos debidos a mosaicos confinados a placenta de la trisomía correspondiente. Se ha valorado la tasa de detección de DUP con respecto al tipo de indicación. Conclusiones. Aunque la DUP es un fenómeno poco frecuente, la gravedad de sus consecuencias clínicas hace absolutamente recomendable su estudio prenatal en las situaciones de riesgo definidas por las normativas internacionales(AU)

Introduction. The usual indication for postnatal uniparental disomy (UPD) testing is a characteristic clinical phenotype present in a patient. The situation in prenatal diagnosis is more complex because the clinical information is much more limited, and the UPD tests are only considered in certain risk situations related to the presence of numerical or structural chromosomal abnormalities in the foetal/placental unit and/or in the parents, or with the ultrasound detection of foetal developmental anomalies or foetal malformations. The objective of this study is to present the experience of our centre in UPD prenatal testing. Methods. A total of 165 UPD prenatal analyses were performed out in our centre since 1998, involving chromosomes 6 (n = 1), 7 (n = 24), 11 (n = 4), 14 (n = 81), and 15 (n = 55), corresponding to 154 gestations; 2 chromosomes have been studied at the same time in 11 of them. Molecular studies were carried out by segregation analysis of polymorphic microsatellite markers distributed along the involved chromosomes. Results. Two maternal UPD cases of chromosomes 7 and 15 were detected, both of them due to confined placental mosaicism of the corresponding trisomy. The detection rate was evaluated with regard to the different indications. Conclusions. Although UPD is a rare phenomenon, the severity of its clinical consequences makes its prenatal study absolutely advisable in the risk situations defined in the international guidelines(AU)