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Basic genetics and patterns of inheritance
Published in Hung N. Winn, Frank A. Chervenak, Roberto Romero, Clinical Maternal-Fetal Medicine Online, 2021
One frequent cause of structural alteration is a translocation. There are two basic types of translocations. A reciprocal translocation occurs when two chromosomes break and the pieces exchange places (Fig. 10). The resulting abnormal chromosomes are called “derivative chromosomes.” If the reciprocal translocation is balanced, the individual is usually normal. Translocations such as these are found in approximately 1 in 500 normal individuals in the general population and are usually never detected. However, if a parent carries a balanced translocation and passes only one of his or her derivative chromosomes to an offspring, along with the other normal chromosomes, the child will have an unbalanced chromosome complement and will likely have multiple problems as a result (Fig. 11). Inheritance of a derivative chromosome in this situation causes a partial duplication (partial trisomy) of one chromosome and a partial deletion (partial monosomy) of another chromosome.
Causes and risk factors
Published in Janetta Bensouilah, Pregnancy Loss, 2021
In 0.3% of cases of spontaneous miscarriage and 3–5% of cases of recurrent miscarriage the cause is parental translocation.8–10 This condition affects one or more rarely both parents, and occurs when a piece of one chromosome breaks off and attaches to another chromosome. In a balanced translocation there is no loss or gain of important genetic material and the person is asymptomatic. However, when they produce eggs or sperm and the cells divide, they only receive half the parental chromosomes. When the individual tries to have children, if fertilisation occurs with one of the abnormal eggs or sperm the embryo will inherit the translocation and either will be a balanced carrier and compatible with normal life, or will be unbalanced and either miscarry or produce abnormalities. Both males and females can be carriers of translocations. There is some evidence that paternal translocations may have less impact on reproductive outcome than those carried by women.2 Even if a couple have had a healthy child, followed by subsequent miscarriages, it is possible that the baby inherited the balanced translocation and therefore survived, but the miscarried babies were chromosomally abnormal. Generally the outlook is positive for balanced translocations, eventually resulting in healthy offspring, and parents with identifiable chromosomal abnormalities should be referred to genetic counsellors for guidance.
Genetics
Published in Rachel U Sidwell, Mike A Thomson, Concise Paediatrics, 2020
Rachel U Sidwell, Mike A Thomson
Here a chromosome 21 is translocated onto another chromosome (14, 15, 21 or 22). This may arise as a new mutation, but in a quarter of these cases one of the parents will have a balanced translocation (see p. 11)
Reproductive outcomes in couples with sporadic miscarriage after embryonic chromosomal microarray analysis
Published in Annals of Medicine, 2023
Zhengyi Xia, Ran Zhou, Yiming Li, Lulu Meng, Mingtao Huang, Jianxin Tan, Fengchang Qiao, Hui Zhu, Ping Hu, Qiaoying Zhu, Zhengfeng Xu, Yan Wang
Embryonic chromosomal abnormalities were the primary cause of SM. The overall prevalence of pathogenic chromosomal abnormalities in miscarriage specimens among SM couples was 60.2%, which is similar to the frequencies of SM (60.6%) and RM (61.2%) previously reported [12]. Consistent with the findings of previous studies, aneuploidy accounted for the largest proportion in SM [13,14]. It is well accepted that large CNVs are causative of miscarriage. We totally detected 35 cases with partial aneuploidy at a prevalence of 3.1%, which is similar to the detection rate identified previously (3.0%) [15]. Terminal deletion accompanied with terminal duplication, which is suggestive of recombinant inversion or unbalanced translocation, was detected in seven (0.6%) cases. Four couples were ultimately identified as balanced translocation carriers by karyotype analysis. These results suggested that segmental chromosomal abnormalities of miscarriages could be caused by parental chromosomal rearrangements, and genetic evaluation of POCs is necessary for these couples to reduce the risk of adverse pregnancy events. Moreover, the detection rate of pathogenic submicroscopic CNVs in SM was 1.1% in this study, which is consistent with the data previously reported (1.1%) [16]. Our findings provide additional evidence that submicroscopic CNVs could be an important cause of miscarriage.
Clinical utility of chromosomal microarray analysis and whole exome sequencing in foetuses with oligohydramnios
Published in Annals of Medicine, 2023
Xiaomei Shi, Hongke Ding, Chen Li, Ling Liu, LiHua Yu, Juan Zhu, Jing Wu
Case 1 harboured a 44.9-Mb duplication in chromosome 10q23.31-q26.3 and a 5.5-Mb deletion in 4p16.3p16.2. The deletion in chromosome 4p16.3p16.2 that was linked to Wolf-Hirschhorn syndrome, a syndrome characterized by typical facial appearance, intellectual disability, developmental delay, seizures, skeletal anomalies, congenital heart defects, and urinary tract malformations [19]. The duplication in chromosome 10q23.31-q26.3 included many OMIM genes associated with typical facial appearance, developmental delay and intellectual disability. This result suggests that one parent may carry a balanced translocation. However, foetus 1 only presented with oligohydramnios. The probable explanation for the paucity of other ultrasound findings is that the gestational age is early and the detection additional anatomic defects in cases of oligohydramnios might be technically challenging. Case 2 had a 3.0-Mb duplication in chromosome 9q34.11q34.13 that contained 21 OMIM genes, which are associated with mild/moderate intellectual disability, dysmorphic features and hypotonia in infancy. As no association between 9q34.11q34.13 microduplication and prenatal sonographic anomalies congenital defects has been reported yet, the association of this variant with oligohydramnios and IUGR in our cohort seems to be merely incidental.
Self-reported effects of perceived social support on marital quality in balanced translocation patients and their spouses undergoing preimplantation genetic testing in China: actor–partner interdependence model
Published in Journal of Obstetrics and Gynaecology, 2022
Fengyi Mo, Xiaorui Hu, Qing Ma, Li Zhang, Lanfeng Xing
Chromosomal abnormalities, one of the most frequent causes of genetic diseases (Mierla et al. 2015), are defined as a genetic disease caused by abnormalities in the number, morphology or structure of chromosomes, often resulting in miscarriage, congenital mental retardation, mental retardation and multiple malformations (Chen et al. 2020). The most frequent chromosomal abnormalities are balanced chromosomal rearrangement, sex chromosomal mosaicism and inversion. The rate of a chromosomal anomaly in the general population is 0.37–1.86%; however, the rate in patients with a history of adverse pregnancy is 3.95–14.3% (Liu et al. 2013). Chromosomal abnormalities cannot be treated medically since they are irreversible (Chen et al. 2020). Balanced translocation is a situation in which both breakage and reconnection of chromosomes occur at abnormal positions, including both Robertsonian and reciprocal translocations. Approximately, 0.5–5% of couples with reproductive problems carry a balanced translocation (Munné et al. 2000; Findikli et al. 2003). However, at present, the specific mechanisms underlying balanced translocation remain unclear (Chen et al. 2020).