X chromosome abnormal inactivation: a unique factor for women's diseases?

Nance-Horan syndrome pedigree due to a novel microdeletion and skewed X chromosome inactivation

BACKGROUND

Nance-Horan syndrome (NHS) is a rare and often overlooked X-linked dominant disorder characterized by dense congenital cataracts, dental abnormalities, and mental retardation. The majority of NHS variations include frameshift mutations, nonsense mutations, microdeletions, and insertions.

METHODS

Copy number variation sequencing was performed to determine the microdeletion. The expression of NHS was detected by RT-PCR. Four family members were tested for X chromosome inactivation.

RESULTS

In this study, all members were examined for systemic examinations and genetic testing of four members and two affected subjects are observed. We identified a heterozygous microdeletion of -0.52 Mb at Xp22.13 in a female proband presenting NHS phenotypically. The microdeletion contains the REPS2 and NHS genes and was inherited from a phenotypically normal mother. Of interest, the expression NHS of proband was reduced and the skewed X chromosome inactivation rate reached more than 85% compared with her mother and the control. It was concluded that the haploinsufficiency of the NHS gene may account for the majority of clinical symptoms in the affected subjects. The variability among female carriers presumably results from nonrandom X chromosome inactivation.

CONCLUSION

Our findings broaden the spectrum of NHS mutations and provide molecular insight into NHS clinical prenatal genetic diagnosis.

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).

Functional Analysis of Ectodysplasin-A Mutations in X-Linked Nonsyndromic Hypodontia and Possible Involvement of X-Chromosome Inactivation

BACKGROUND

Mutations of the Ectodysplasin-A (EDA) gene are generally associated with syndrome hypohidrotic ectodermal dysplasia or nonsyndromic tooth agenesis. The influence of EDA mutations on dentinogenesis and odontoblast differentiation has not been reported. The aim of this study was to identify genetic clues for the causes of familial nonsyndromic oligodontia and explore the underlying mechanisms involved, while focusing on the role of human dental pulp stem cells (hDPSCs).

MATERIALS AND METHODS

Candidate gene sequences were obtained by PCR amplification and Sanger sequencing. Functional analysis was conducted, and the pathogenesis associated with EDA mutations in hDPSCs was investigated to explore the impact of the identified mutation on the phenotype. Capillary electrophoresis (CE) was used to detect X-chromosome inactivation (XCI) in the blood of female carriers.

RESULTS

In this study, we identified an EDA mutation in a Chinese family: the missense mutation c.1013C>T (Thr338Met). Transfection of hDPSCs with a mutant EDA lentivirus decreased the expression of EDA and dentin sialophosphoprotein (DSPP) compared with transfection of control EDA lentivirus. Mechanistically, mutant EDA inhibited the activation of the NF-κB pathway. The CE results showed that symptomatic female carriers had a skewed XCI with a preferential inactivation of the X chromosome that carried the normal allele.

CONCLUSIONS

In summary, we demonstrated that EDA mutations result in nonsyndromic tooth agenesis in heterozygous females and that, mechanistically, EDA regulates odontogenesis through the NF-κB signalling pathway in hDPSCs. Due to the large heterogeneity of tooth agenesis, this study provided a genetic basis for individuals who exhibit similar clinical phenotypes.

X chromosome-linked long noncoding RNA lnc-XLEC1 regulates c-Myc-dependent cell growth by collaborating with MBP-1 in endometrial cancer

LncRNAs (long noncoding RNAs) are noncoding transcripts that are more than 200 nt long and have been described as the largest subclass in the noncoding transcriptome in humans. Although studies of lncRNAs in cancer have been continuing for a long time, no much has been known about X chromosome-linked lncRNAs. Here, by using RNA-seq we report the identification of a new X chromosome-linked lncRNA (lnc-XLEC1) that is aberrantly downregulated during the development of endometrial carcinoma (EC). The overexpression of lnc-XLEC1 reduces the migration and proliferation of EC cells. Flow cytometry analysis indicated that lnc-XLEC1 overexpression resulted in a substantial accumulation of EC cells in the G1 phase. In addition, lnc-XLEC1 had inhibitive effects that may result from its collaboration with MBP-1 during the suppression of the c-Myc expression and the negative regulating of the Cdk/Rb/E2F pathway. The anti-tumor effects of lnc-XLEC1 on EC progression suggest that lnc-XLEC1 has some potential value in anti-carcinoma therapies and deserves further investigation. Our study reported for the first time that the lnc-XLEC1 might be related to the incidence and prognosis of EC. Moreover, we discovered that this process might be related to somatic X dosage compensation and skewed X chromosome inactivation (SXCI).