Aneuploid rescue precedes X-chromosome inactivation and increases the incidence of its skewness by reducing the size of the embryonic progenitor cell pool

Investigation of the role of X chromosome inactivation and androgen receptor CAG repeat polymorphisms in patients with recurrent pregnancy loss: a prospective case-control study

BACKGROUND

Previous research has revealed that skewed X chromosome inactivation (SXCI) and androgen receptor (AR) CAG polymorphisms are associated with increased risk of recurrent pregnancy loss (RPL); however, the results are conflicting, and the underlying mechanisms remain unclear. This study investigated the role of SXCI and AR CAG polymorphisms in patients with RPL and explored whether the underlying mechanisms were related to the ovarian reserve and preimplantation embryo aneuploidy.

METHODS

This was a prospective case-control study carried out in a tertiary hospital-based reproductive medicine center. An external validation RPL cohort was recruited during the study period. Data on baseline and cycle characteristics were collected. X-chromosome inactivation (XCI) was measured using a human AR assay. AR polymorphisms were assessed using quantitative fluorescent polymerase chain reactions and direct sequencing. Blastocysts of the patients with RPL were tested by single nucleotide polymorphism microarray based preimplantation genetic testing for aneuploidy.

RESULTS

In total, 131 patients with idiopathic RPL and 126 controls were included for the case-control study. Patients with RPL exhibited a significantly more skewed XCI distribution pattern (67.71 ± 10.50 vs. 64.22 ± 10.62, p = 0.011), as well as significantly shorter bi-allelic mean (18.56 ± 1.97 vs. 19.34 ± 2.38, p = 0.005) and X-weighted bi-allelic mean (18.46 ± 2.02 vs. 19.38 ± 2.53, p = 0.001) of AR CAG repeats. Multivariate logistic regression models indicated that CAG repeat < 20, SXCI, and duration of stimulation were independently associated with the risk of RPL. However, SXCI and AR CAG polymorphisms were not associated with ovarian reserve or preimplantation embryo aneuploidy in the RPL group, and the same results were attained in a separate validation cohort of 363 patients with RPL.

CONCLUSION

SXCI and AR CAG polymorphisms are related to RPL; however, these two factors do not lead to RPL by affecting the ovarian reserve or increasing embryo aneuploidy. The roles of SXCI and AR CAG in RPL may involve other mechanisms that require further investigation.

TRIAL REGISTRATION

NCT02504281, https://www.

CLINICALTRIALS

gov (Date of registration, 21/07/2015; date of enrolment of the first subject, 30/07/2015).

Uniparental disomy is a chromosomic disorder in the first place

Background

Uniparental disomy (UPD) is well-known to be closely intermingled with imprinting disorders. Besides, UPD can lead to a disease by ‘activation’ of a recessive gene mutation or due to incomplete (cryptic) trisomic rescue. Corresponding to all common theories how UPD forms, it takes place as a consequence of a “chromosomic problem”, like an aneuploidy or a chromosomal rearrangement. Nonetheless, UPD is rarely considered as a cytogenetic, but most often as a molecular genetic problem.

Results

Here a review on the ~ 4900 published UPD-cases is provided, and even though being biased as discussed in the paper, the following insights have been given from that analysis: (1) the rate of maternal to paternal UPD is 2~3 to 1; (2) at most only ~ 0.03% of the available UPD cases are grasped scientifically, yet; (3) frequencies of single whole-chromosome UPDs are non-random, with UPD(16) and UPD(15) being most frequent in clinically healthy and diseased people, respectively; (4) there is a direct correlation of UPD frequency and known frequent first trimester trisomies, except for chromosomes 1, 5, 11 and 18 (which can be explained); (5) heterodisomy is under- and UPD-mosaicism is over-represented in recent reports; and (6) cytogenetics is not considered enough when a UPD is identified.

Conclusions

As UPD is diagnosed using molecular genetic approaches, and thus by specialists considering chromosomes at best as a whim of nature, most UPD reports lack the chromosomal aspect. Here it is affirmed and substantiated by corresponding data that UPD is a chromosomic disorder in the first place and cytogenetic analyses is indicated in each diagnosed UPD-case.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13039-022-00585-2.

Random X chromosome inactivation in patients with Klinefelter syndrome

Background

X chromosome inactivation (XCI) is an indispensable process in the development of human female embryos. Reportedly, XCI occurs when a blastocyst contains 10–12 embryonic progenitor cells. To date, it remains unclear whether XCI ratios are normally preserved in Klinefelter syndrome (KS) patients with 47,XXY karyotype.

Methods

We examined XCI ratios in 18 KS patients through DNA methylation analysis for the polymorphic trinucleotide locus in the AR gene. The results of the KS patients were compared to previous data from healthy young women.

Results

XCI ratios in KS patients followed a normal distribution. Skewed XCI was observed in two patients, one of whom exhibited extremely skewed XCI. The frequencies of skewed and extremely skewed XCI in the KS cohort were comparable to those in healthy women.

Conclusion

This study confirmed the rarity of skewed XCI in KS patients. These results indicate that the presence of a supernumerary X chromosome during the cleavage and early blastocyst stages does not affect the developmental tempo of embryos. Our data deserve further validation.