The term autosomal reciprocal translocation (ART) is applied to chromosomal rearrangement involving the exchange of chromatin fragments between non-homologous chromosomes. Universal characteristics of ARTs include quadrivalent asymmetry, the presence of terminal breakpoints, and the length of translocated (TS) and centric segments (CS). In addition, participation in a translocation of chromosome 9 and acrocentric autosomes are known to affect pathological meiotic segregation mode^{[ 1 , 2 , 3 , 4 ]}.

Here, we describe a rare case of a family in which both parents carry independently acquired ARTs. We performed chromosome segregation analysis in both the sperm and blastomeres depending on the universal characteristics of the ARTs. These data were then evaluated and discussed in the context of their applicability for genetic counseling and the prediction of reproductive outcomes in such couples based on both translocation feature and the carrier’s gender.

A non-consanguineous couple with a 2-year history of infertility, asthenozoospermia in the male, obesity in the female, and without other phenotypic features was referred to the International Centre for Reproductive Medicine for the first time in 2014, when the female was 28 and the male was 36 years of age. Karyotype analysis of each spouse revealed that both present with unique ARTs: 46,XY,t(3;6)(p22.2;p21.2) and 46,XX,t(2;17)(p16.1;p12) ( Fig. 1A and B ).

Couple then underwent 7 years (2014–2020) of treatment including 6 cycles of in vitro fertilization or intra-cytoplasmic sperm injection and 3 balanced embryo transfers following PGT-SR evaluation by fluorescent in situ hybridization or array comparative genomic hybridization (aCGH), resulting in a single pregnancy and the birth of a healthy son. Both spouses refused prenatal karyotyping and karyotype analysis of their son after birth revealed his inheritance of the maternal translocation: 46,XY,t(2;17)(p16.1;p12)mat ( Fig. 1C ).

Estimation of the length of both the TS and CS, the sum of these lengths, and their ratio allows us to predict that the most likely pathological segregation mode for both translocations is adjacent-1 ( Supplementary Table 1 ; http://links.lww.com/RDM/A8).

The female t(2;17) contributes to the formation of a severe asymmetric quadrivalent, while translocation in the male t(3;6) to a mild asymmetric quadrivalent. Both translocations have no terminal breakpoints ( Supplementary Table 2 ; http://links.lww.com/RDM/A8).

Our evaluations identified an alternate mode of segregation in 41.7% of the embryos regardless of translocation. Adjacent-1 was the predominant pathological mode of segregation in both translocations (33.3% in female and 29.2% in male), followed by 3:1 (12.5%) and adjacent-2 (4.2%) in the female, and adjacent-2 (12.5%) and 3:1 (8.3%) in the male. In addition, we could not define the segregation type in 2 embryos when evaluating the male translocation and two embryos in the female translocation ( "other" type of segregation; 8.3% in both) owing to inconsistencies in the number of fluorescent signals or chromosome content specific to a particular segregation mode. Examples of the PGT-SR results are shown in Figure 1 .

The most common segregation mode in the sperm was alternate (40.6%). The prevalent pathological segregation type was adjacent-1 (35.3%). Segregation of 3:1 and adjacent-2 were detected in 18.8% and 5.3% of the sperm nuclei, respectively.

ART carriers are at an increased risk of infertility, recurrent miscarriage, and chromosomally abnormal offspring due to pathological chromosome segregation during gametogenesis. Effective genetic counseling combines empirical data and segregation analysis to determine the probability of having an offspring with an unbalanced karyotype or experiencing a miscarriage. However, the empirical data describing the risks for families in which both partners are ART carriers is extremely limited. This is further complicated by the fact that ARTs are not recurrent, making the application of broader empirical data difficult. In addition, comprehensive segregation analysis requires the investigation of extended pedigrees which must include various family members with known karyotypes, making these evaluations largely impractical. However, the use of universal ART characteristics (length of TS and CS, quadrivalent asymmetry, presence of terminal breakpoints) can provide additional insight into these translocations and may be useful in genetic counseling and more broadly applied.

Alternate segregation type is frequent in ART carriers. Its high incidence can be explained, at least in part, in male carriers by the lack of complete maturation of unbalanced gametes due to failure of the spermatozoa to pass the spermatogenesis checkpoints^{[ 1 , 5 ]}. Analysis of chromosome segregation patterns in both the sperm and embryos for male translocation in our case also showed an alternate segregation mode as common.

Alternate segregation is significantly less frequent in ART carriers with severe asymmetric quadrivalents or with terminal breakpoints when compared to those with mild asymmetric quadrivalents or without terminal breakpoints. In contrast, the 3:1 mode is more common in severe asymmetric quadrivalents^{[ 3 , 4 ]}. Here, we noted that the female ART presented with severe quadrivalent asymmetry while the male translocation induced only mild quadrivalent asymmetry, both rearrangements were without terminal breakpoints. The predominant pathological type was found to be adjacent-1 for both translocations when predicted using both the TS and CS lengths. We detected 3:1 segregation in 12.5% of female ART embryos compared to 8.3% in male ART embryos, but the differences were not significant. However, despite the lack of significance, this observation is consistent with our evaluation of severe quadrivalent asymmetry in the female ART inducting pathological meiotic disjunctions.

The inheritance of a maternal translocation by a son requires investigation of the possible effect of this translocation on his reproductive potential not only due to the formation of the severe asymmetric quadrivalent but also to the localization of breakpoints. One of the breakpoints is located in 17p12 fragile site, but it is known that homozygosity at the 17p12 does not affect reproductive function^{[ 6 ]}. However, an investigation of the frequency and origin of segmental aneuploidy in human oocytes and pre-implantation embryos revealed that some chromosome breakpoints tend to occur within known fragile sites^{[ 7 ]}. Even though most segmental aneuploidies are of mitotic origin, it is not known as to how the initial presence of a breakpoint in any of the fragile sites in a translocation carrier influences the processes of double-stranded breakage and reunion during crossing-over in spermatogenesis, in which, unlike oogenesis, there is an inefficient repair of DNA damage^{[ 8 ]}.

As for the second breakpoint in the female translocation, there is no evidence that any of the genes located in the 2p16.1 region affect fertility. Furthermore, it is known that the FSHR gene does not affect sperm count^{[ 9 ]}. CCDC85A has been associated with female fertility in some studies, but the effect on the male reproductive system has not been evaluated^{[ 10 ]}.

In addition, polymorphisms and copy number variation of the EFEMP1 gene, located at 2p16.1, have been associated with abdominal obesity^{[ 11 ]}, which may explain the presence of obesity in the female partner.

PGT-SR is a necessary and urgent measure for most families in which both spouses are ART carriers, as this technique can help them have a healthy baby^{[ 12 , 13 , 14 ]}. The lack of empirical data, as well as the complexity of segregation analysis, require additional tools for risk assessment in families with double translocations. Estimations of the theoretically predicted type of pathological chromosome segregation, the presence of terminal breakpoints, the asymmetry degree and segregation mode in the sperm are all likely to be useful during genetic counseling. To the best of our knowledge, this is the first study to describe the universal characteristics of ARTs in a family with 2 different translocations. Even though these parameters are informative for families with one ART, it is still premature to draw any conclusions around their application in double translocation families. Thus far, the available data suggests that it may be possible to advise these families on the use of a sperm or egg donor in the case of severe quadrivalent asymmetry, advanced maternal age and multiple unsuccessful attempts to obtain embryos with a balanced karyotype. At the same time, considering the frequency of alternate segregation and the limited empirical data available regarding such exceptionally rare cases, it is necessary to precisely assess the risks for each individual family to support their pursuit of a healthy offspring without the use of donor gametes, as in this case.