General conditions
Twelve BCCR couples diagnosed by karyotype analysis of peripheral blood were recruited including four female BCCR carriersand eight male BCCR carriers. 17 PGT cycles wereperformed. All twelve couples had negative reproductive history.Twelve BCCR couples were divided into three groups such as four couples of three-way rearrangements carriers(group A), three couples of double two-way translocations carriers(group B) and five couples of exceptional CCR carriers(group C)(Table 1).There were no significantly statistical differences among the three groups within the baseline information (Table 2).
Controlled ovarian stimulation(COS)outcome of the PGT cycles for BCCR couples
After undergoing 17 cycles of COS in12 couples, a total of 243 oocytes were retrieved, including 207 mature oocytes (MII), and 181 (87.43%) oocytes were observed as two-pronuclear embryos (2PN) after intracytoplasmic sperm injection (ICSI). Then, 83 embryos were biopsied, including 8 embryos at the cleavage stage and 75 blastocysts. The rates of 2PN in group A, B and C were 69.47%(66/95), 83.33%(45/54) and 74.46%(70/94). And there was no significant differences among the three groups (χ2=3.48, P=0.18, P>0.05). The rates of embryos formation on day3 of three groups were 87.88%(58/66), 97.78%(44/45) and 77.14%(54/70), which was significantly different (χ2=10.05, P=0.01, P<0.05). Further analysis indicated that compared with group B, the rate of embryo formation was statistically significantly lower in group C (χ2=7.69, P=0.01, P<0.02). The rates of high-quality embryos on day3 in three group were 70.68%(41/58), 79.55%(35/44) and 75.93%(41/54) respectively, and there was no significant differences(χ2=1.08, P=0.58, P>0.05).
The rate of blastocyst formation on D5/6 were 51.52%(34/66), 60.00%(27/45) and 38.57%(27/70), which was also no significant differences(χ2=5.38, P=0.07, P>0.05). However, the rates of high-quality blastocysts in three group were 14.71%(5/34), 48.15%(13/27) and 62.96%(17/27), which was significantly different (χ2=15.77, P=0.00, P<0.05). Compared with groups B and C, the rate of high-quality blastocysts in group A was statistically significantly lower (χ2=8.09, P=0, χ2=15.20, P=0, P<0.02)(Table 3).
Embryo identification of the PGT cycles for BCCR couples
Eighty three embryos were biopsied, including 28 blastocysts in group A，8 cleavage embryos and 22 blastocysts in group B and 25 blastocysts in group C. After comprehensive chromosome analysis, the total euploid embryo rate was 9.09% (7/77), the total aneuploidy rate was 90.91% (70/77), and 6 failed to amplify (Table S1).
Among them, the euploid embryo rate was 10.71%(3/28) and the aneupliodyrate was 89.29%(25/28) in group A. The euploid embryo rate was 3.85%(1/26), the aneupliody rate was 96.15%(25/26), and 4 embryos failed to diagnose in group B. The euploid embryo rate was 13.04%(3/23), theaneupliody rate was 86.96%(20/23), and 2 embryos failed to amplify in group C. There were no significant differences among the three groups (Fisher exact probabilities P = 0.55, P> 0.05).
Due to the rarity of BCCR carriers, in order to increase sample size to explore the impact of BCCR on embryonic molccular karyotype, wecollecteddata from PGT for BCCR carriers reported in PubMed up to now. Frumkin T et al. reported a couple in which the husband was a three-way rearrangements carrier with one PGT cycle, who had 2 euploid embryos and 5 abnormal embryos[12]. Chan Tian et al. reported a couple in which the male partner was an exceptional CCR carrier with one PGT cycle, who had no euploid embryos and 2 aneuploid embryos[13]. E. Vanneste et al. reported a couple in which the husband was an exceptional CCRs carrier with two PGT cycles, who had 4 balanced or normal embryos and 12 abnormal embryos[14]. Paul et al. reported 4 couples, including 3 males and 1 female three-way rearrangements carriers with 6 PGT cycles, who had 6 euploid embryos and 31 aneuploid embryos[10]. Hu L et al.reported 7 couples, including 5 couples with three-way rearrangements, who had 3 balanced or normal embryos, 31 abnormal embryos and one embryo of amplification failure, and 1 couple with double two-way translocations, who had no balanced or normal embryos and 12 abnormal embryos[1]. Brunet BCFK et al. reported 3 couples with three-way rearrangements with 4 cycles, who had 3 balanced or normal embryos and 15 abnormal embryos, and 1 double two-way translocations who had no balanced or normal embryos and 2 abnormal embryos in one cycle[11]. Therefore, in summary, the euploid embryo rate and aneuploidy rate were 13.71%(17/124) and 86.29%(107/124) ingroup A. The euploid embryo rate was 2.5%(1/40) and the aneuploidy rate was 97.5%(39/40) in group B. Theeuploid embryo rate was 17.07%(7/41) and the aneuploidy rate was 82.93%(34/41)in group C, respectively. (Fig 1). There was no significant difference in the embryonic molecular karyotypes among the three groups (Fisher exact probabilities P = 0.08, P> 0.05).
Clinical outcome of PGT cycles for BCCR couples
In the 17 PGT cycles, there were 13 cycles in which no euploid embryo could be transplanted and 4 cycles in which euploid embryos were transplanted with frozen-thawed embryo transfer. Two of the 4 cycles was clinically pregnant, and the prenatal diagnosis at 16 weeks of gestation was 46, XN and 46, XN, t(8,13,10)(q21;q31;p15)，(XN means XX or XY).The outcome mentioned that euploid embryos of NGS-PGT for BCCR maybe the balanced translocation carriers.(Fig 2) Fortunately, two boys were born alive and healthy.