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Genetic Counseling in Assisted Reproductive Technology
Published in Carlos Simón, Carmen Rubio, Handbook of Genetic Diagnostic Technologies in Reproductive Medicine, 2022
Sporadic aneuploidy is a random occurrence and refers to aneuploidy that is not inherited. Errors during maternal meiosis are the most frequent cause of sporadic aneuploidy in embryos. Chromosomal rearrangements, such as translocations and inversions, can be passed on from generation to generation in the balanced form and can also result in imbalances, causing developmental abnormalities in offspring. Recurrent aneuploidy of the acrocentric chromosomes can be caused by a Robertsonian translocation carried by one member of the reproductive couple. Recurrent aneuploidy, especially recurrent segmental aneuploidy, can be caused by a balanced reciprocal translocation or inversion in a carrier parent.
Assessment of fetal genetic disorders
Published in Hung N. Winn, Frank A. Chervenak, Roberto Romero, Clinical Maternal-Fetal Medicine Online, 2021
Teresa Martino, J. Pratt Rossiter, Karin J. Blakemore
In recent years, there has been a greater focus on using cell-free fetal DNA or RNA within the maternal plasma or serum for use in prenatal DNA diagnosis. In 1997, Lo et al. demonstrated that cell-free fetal DNA circulates within the plasma and serum of pregnant women (121). Fetal DNA can be detected within the maternal circulation as early as 7 weeks of gestation (122). In 2009, Tobias et al. reported a method of specific magnetic bead-based capture of free fetal DNA from maternal plasma. The team developed a magnetic capture hybridization technique using specific hybridization primers for the extraction of fetal DNA from maternal plasma, which is almost twice as efficient as older methods (123). Both forms of nucleic acids may prove useful for accurate fetal gender determination and fetal RhD blood typing. Their utility for screening and/or detection of fetal aneuploidy remains under active investigation.
Preimplantation Genetic Testing for Aneuploidies: Where We Are and Where We're Going
Published in Darren K. Griffin, Gary L. Harton, Preimplantation Genetic Testing, 2020
Andrea Victor, Cagri Ogur, Alan Thornhill, Darren K. Griffin
Aneuploidy is a disorder of chromosome number. Its classical definition in humans describes any deviation of 23 or its multiples in chromosome count. The most commonly encountered forms of aneuploidy in embryos are trisomies, in which an individual chromosome is present in triplicate, or monosomies, where only one copy is present, resulting in 47 or 45 chromosomes per cell, respectively. Chromosomes can also be present in multiple copies (tetrasomy, pentasomy, polysomy) or none at all (nullisomy), and more than one chromosome can be affected in the karyotype (double aneuploids, complex aneuploids).
Recurrent Medical Termination of Pregnancy, Not Always the Same Pathology
Published in Fetal and Pediatric Pathology, 2021
The recurrence of the same chromosomal abnormality may also require parental karyotype, especially when suspecting parental mosaicism. Depending on the degree and genes involved, the carrier of a somatic or germline mosaicism may be either asymptomatic or present a variety of manifestations of genomic imbalance (growth and developmental delay, congenital malformations, cognitive and neurological impairment), reproductive issues (infertility and recurrent miscarriages), as well as a high risk of affected progeny. Segmental mosaicism is not as frequent as mosaicism for whole chromosomes, with calculated frequencies of 0.02 and 0.005%, for balanced and unbalanced autosome rearrangements, respectively [15,16]. A remarkable feature is a strong female preponderance among carriers of mosaicism for chromosomal structural rearrangements with pericentromeric breaks, indicating female-specific instability in early human embryos [11,15,17]. In our series, there were no recurrences of the same aneuploidy; one case of structural mosaicism and another due to numeric abnormality (trisomy 13) were found, both of them non-recurrent. Our only case of structural mosaicism corresponded to a male genotype.
BACs-on-Beads™ assay for a case of trisomy 22 confined placental mosaicism
Published in Journal of Obstetrics and Gynaecology, 2021
Guoxing Zhong, Hailin He, Zeyan Zhong, Jianhong Chen
If a positive result of the suspected aneuploidy was found with CVS, further testing was required to confirm the diagnosis from amniocentesis (Mardy and Wapner 2016). In this case, we found a 22q11.2 microduplication in CVS. Considering the ultrasound results, AF was further verified, karyotype analysis showed small proportion of trisomy 22 mosaicism (mos 47, XN, +22[2]/46, XN[199]), and the BoBs™ assay was normal. After birth, karyotype of the girl revealed no abnormalities (46 XX), which suggested that mosaicism was limited to the placenta. Finally, we confirmed this through placental testing. A previous case also found a low-level mosaicism of X monosomy (mos 45, X[5]/46, XX[95]) in amniocentesis but normal in the newborn (Serapinas et al. 2016). The advantages provided by CVS was an earlier gestational age diagnosis of abnormalities than an amniocentesis (11–13 versus 15–18 weeks), it remained a preferred test method for many prospective parents who carried known monogenic hereditary diseases (Gu et al. 2018). But CPM occurred in 1–2% of pregnancies assessed by CVS (Bunnell et al. 2017). In our study, the BoBs™ assay for CVS was 22q11.2 microduplication, but the QF-PCR result was normal. A retrospective study indicated that BoBs™ assay was similar to QF-PCR in detecting trisomy 13, trisomy 18, trisomy 21 and sex chromosomal aneuploidies, but it was superior to QF-PCR in detecting major structural abnormalities (53.3 versus 13.3%) and mosaicism (28.6 versus 0%) (Choy et al. 2014).
Fetal screening and whole genome sequencing: where are the limits?
Published in Expert Review of Molecular Diagnostics, 2021
Susan Hancock, Katherine Johansen Taber, James D. Goldberg
Prenatal aneuploidy screening, specifically for Down syndrome, and carrier screening for inherited genetic conditions like cystic fibrosis and hemoglobinopathies, have existed for decades. At first, high risk for aneuploidy was identified using maternal age alone. However, incremental improvements in performance were achieved over time with the addition of maternal serum and ultrasound markers. In general, these traditional modes of aneuploidy screening led to improved sensitivity for Down syndrome, but specificity remained relatively low, with a 5% false-positive rate (FPR) held as the acceptable threshold, resulting in positive predictive values (PPV) of <5% in even the most comprehensive forms of screening. Carrier screening has also improved incrementally, with initial approaches based on reported patient ethnicity alone, such as sickle cell screening by hemoglobin analysis for individuals of African descent. As the deleterious genetic variants for a variety of inherited conditions were characterized, carrier screening recommendations expanded to include more conditions for more ethnicities, but disparities persisted because of low detection rates in some patient populations.