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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
Although carriers of a balanced chromosomal rearrangement are generally healthy, the rearrangement can cause difficulties conceiving or carrying a child to term. The most common balanced structural rearrangements are translocations, in which segments from two chromosomes dissociate and then rejoin to the reciprocal chromosome, and inversions, where a segment of a single chromosome disassociates but then rejoins in the opposite orientation. Robertsonian translocations are unique types of translocations that involve the acrocentric chromosomes 13, 14, 15, 21, and 22. The chromosomes fuse at the centromere, resulting in a reduction in the total number of chromosomes and the benign loss of the redundant stalks and satellites at the p arm of both chromosomes. A balanced chromosomal rearrangement can lead to difficulty conceiving, spontaneous miscarriage, or the birth of a child with multiple congenital anomalies, depending on the degree of the imbalance. Although balanced in the carrier, structural rearrangements may be unbalanced in the gametes, resulting in developmental abnormalities. In some individuals, the structural rearrangement can impair meiosis and block gametogenesis, especially male spermatogenesis. The disruption of spermatogenesis is variable, even among male relatives carrying the same chromosomal rearrangement. Approximately 1/500 individuals in the general population carry a balanced reciprocal translocation, and approximately 1/1000 individuals carry a balanced Robertsonian translocation. This frequency is likely to be higher in the infertile population.
Prenatal Diagnosis and Screening for Aneuploidy
Published in Vincenzo Berghella, Obstetric Evidence Based Guidelines, 2022
Sarah Harris, Angie Jelin, Neeta Vora
With full trisomy 21, the recurrence risk is empirically 1% or the age-related risk. With Robertsonian translocation, parental chromosomes should be checked, with genetic counseling regarding specific future risks. A Robertsonian translocation between two chromosomes 21, t(21;21) has a 100% risk for trisomy 21 when transmitted by a carrier parent. Also rare is a non-Robertsonian translocation formed by the union of two 21s such that the translocation forms a mirror image of the normal 21. Some literature suggests that in some families where there have been recurrent trisomies, a relationship exists with their MTHFR status. This has not been proven in large studies.
Common Tips on Communication
Published in Justin C Konje, Complete Revision Guide for MRCOG Part 3, 2020
Abnormalities in chromosomes are common and typically occur at the time eggs, and sperms are formed. A typical way in which these occur is through a process called translocation. Translocation Down syndrome, for example, is the only type of Down syndrome that can be passed down from a parent who does not have the features of Down syndrome. If a parent has a balanced translocation, there is up to 15% chance of having another child with Down syndrome. A balanced or chromosomal translocation is a condition in which part of a chromosome has broken off and reattached in another location. This is usually the case for reciprocal (or balanced) translocation, a type of chromosomal translocation that increases the risk of recurrent miscarriages. The other type of translocation is Robertsonian translocation.
Extending Phenotypic Spectrum of 17q22 Microdeletion: Growth Hormone Deficiency
Published in Fetal and Pediatric Pathology, 2021
Ceren Damla Durmaz, Şule Altıner, Elifcan Taşdelen, Halil Gürhan Karabulut, Hatice Ilgın Ruhi
Reciprocal translocation which is one of the structural chromosomal abnormalities occurs approximately in 1 in 500 people [7]. The translocation may have arisen de novo in the person, or it may be inherited. Mostly de novo reciprocal translocations occur in male meiosis. During spermatogenesis, it can be assumed that some cells escape from the mechanism that controls the correct crossing-over, they are exposed to a chaotic fracture, and the broken parts are subjected to exonuclease degradation [8, 9]. Whereas most de novo Robertsonian translocations arise during oogenesis [10]. Cryptic deletions have been reported in approximately 40% of phenotypically abnormal patients with apparently balanced chromosomal abnormalities [8, 11]. Mechanisms of the deletion at the breakpoints are still unclear.
Current updates and future perspectives in the evaluation of azoospermia: A systematic review
Published in Arab Journal of Urology, 2021
Nahid Punjani, Caroline Kang, Dolores J. Lamb, Peter N. Schlegel
In addition to the use of karyotyping to look for abnormalities such as KS, chromosomal translocations may provide further insight into the aetiology of azoospermia. In general, infertile men have a nine-times greater rate of chromosomal translocation (balanced, unbalanced and possible mosaic) compared to the general population [63]. Robertsonian translocations are the most common type of translocation consisting of a specific subgroup of autosomal structural abnormalities that occur between the five acrocentric chromosomes (13, 14, 15, 21, and 22) that are typically associated with oligozoospermia and NOA (although some men have normal semen parameters), which result in unbalanced translocations, mono- or trisomy, uniparental disomy in the offspring, and spontaneous miscarriage [65].
Contemporary genetics-based diagnostics of male infertility
Published in Expert Review of Molecular Diagnostics, 2019
Alberto Ferlin, Savina Dipresa, Andrea Delbarba, Filippo Maffezzoni, Teresa Porcelli, Carlo Cappelli, Carlo Foresta
Chromosomal translocations can affect male fertility and pregnancy outcome [4,10–12,15,37,38] and, in particular, males with reciprocal translocations have a high rate of unbalanced spermatozoa due to meiotic segregation errors [39,40]. Therefore, genetic counseling and analysis of chromosomal constitution in sperm or pre-implantation genetic diagnosis is suggested in order to assess the risk of transmission of unbalanced forms. From a quantitative point of view, translocations may be balanced (no loss of quantity of DNA), or unbalanced (with loss of DNA). Reciprocal translocations involve an exchange of genetic material between two or more chromosomes, they are the most common chromosomal structural anomalies in humans and are 10 times more common among infertile men [4,10–12,15,37,38]. The most frequent translocations in infertile patients are robertsonian translocations or centric fusions [4,10–12,15,37,38]. Robertsonian translocations occur with an incidence of 0.9% of men with severe male factor infertility [35]. These occur among acrocentric chromosomes (chromosomes 13, 14, 15, 21, and 22): the long arms of two chromosomes fuse resulting in loss of genetic material of the chromosomal short arms (final complement of 45 chromosomes). The most common robertsonian translocations detected in infertile men include t(13q;14q) and t(14q;21q). As men with reciprocal translocations, men with robertsonian translocations are generally phenotypically normal, but spermatogenesis might be impaired and a high rate of unbalanced sperm might be found [41].