Association of Extremely Skewed X-chromosome Inactivation with Taiwanese Women Presenting with Recurrent Pregnancy Loss

X-chromosome inactivation (XCI) is a phenomenon that occurs in female mammals. Typically, maternally- and paternally-derived X chromosomes are inactivated at approximately the same frequency. If preferential inactivation occurs, the person is considered to have skewed XCI. Skewed XCI has been reported to occur more frequently in women who experience recurrent pregnancy loss (RPL). In this study, we sought to investigate if there is an association between skewed XCI and unexplained RPL in Taiwanese women. A total of 194 women who had experienced unexplained RPL were recruited into the study. Human androgen receptor or DXS6673E and DX15-134 loci were used in the XCI assay. The results of our study suggested that a cut-off point < 90% may not be justified for skewed XCI. Only extremely skewed (> 95%) XCI is associated with RPL. Extremely skewed XCI occurs in a subset of Taiwanese women with RPL.