Abstract
PurposeThe purpose of this study was to compare meiotic segregation in sperm cells from two carriers with t(4;8)(p16;p23.1) reciprocal chromosome translocations (RCTs), differing in localization of the breakpoint positions at the 4p subband—namely, 4p16.3 (carrier 1) and 4p16.1 (carrier 2)—and to compare data of the pedigree analyses performed by direct method.MethodsThree-color fluorescent in situ hybridization (FISH) on sperm cells and FISH mapping for the evaluation of the breakpoint positions, data from pedigrees, and direct segregation analysis of the pedigrees were performed.ResultsSimilar proportions of normal/balanced and unbalanced sperm cells were found in both carriers. The most common was an alternate type of segregation (about 52 % and about 48 %, respectively). Unbalanced adjacent I and adjacent II karyotypes were found in similar proportions about 15 %. The direct segregation analysis (following Stengel-Rutkowski) of the pedigree of carriers of t(4;8)(p16.1;p23.1) was performed and results were compared with the data of the pedigree segregation analysis obtained earlier through the indirect method. The probability of live-born progeny with unbalanced karyotype for carriers of t(4;8)(p16.1;p23.1) was moderately high at 18.8 %—comparable to the value obtained using the indirect method for the same carriership, which was 12 %. This was, however, markedly lower than the value of 41.2 % obtained through the pedigree segregation indirect analysis estimated for carriers of t(4;8)(p16.3;p23.1), perhaps due to the unique composition of genes present within the 4p16.1–4p 16.3 region.ConclusionsRevealed differences in pedigree segregation analysis did not correspond to the very similar profile of meiotic segregation patterns presented by carrier 1 and carrier 2. Most probably, such discordances may be due to differences in embryo survival rates arising from different genetic backgrounds.
Highlights
Carriership of a reciprocal chromosome translocation (RCT) is one of the underlying conditions resulting inJ Assist Reprod Genet (2016) 33:189–197 live-born offspring with chromosomal imbalances and may lead to unfavorable pregnancy outcomes such as miscarriages, stillbirths, and early newborn deaths
Revealed differences in pedigree segregation analysis did not correspond to the very similar profile of meiotic segregation patterns presented by carrier 1 and carrier 2
Clinical effects vary due to the different forms of the unbalanced gametes produced during the meiotic segregation of chromosomes involved in RCT
Summary
Carriership of a reciprocal chromosome translocation (RCT) is one of the underlying conditions resulting inJ Assist Reprod Genet (2016) 33:189–197 live-born offspring with chromosomal imbalances and may lead to unfavorable pregnancy outcomes such as miscarriages, stillbirths, and early newborn deaths. Knowledge of the meiotic patterns of segregation of RCT carriers, as compared to empirical data on segregation from pedigree analysis, may be useful in illustrating the natural selection of children due to various chromosomal imbalances in different prenatal and postnatal periods of development. Such results may prove valuable for genetic counseling of RCT carrier families [2,3,4]. The t(4;8)(p16;p23) translocations in humans are not unique, since they arise independently in unrelated individuals This is due to the repetitive sequences (LTR) of the olfactory receptor (OR) gene clusters at 4p16.1 and 4p16.3 and at 8p23.1. These repetitive sequences likely facilitate recurrent nonallelic homologous recombinations (NAHR) between both nonhomological chromosomes [11,12,13,14]
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