Background: Fabry Disease (FD) is an X-linked lysosomal disease, in which, unlike other X-linked disorders, most female carriers manifest signs or symptoms for unknown reasons. Objectives: Herein, we aimed to test the potential role of X-chromosome inactivation (XCI) in leukocytes as a prognostic biomarker of disease in FD female carriers. Moreover, we explored if levels of X-inactive-specific transcript (Xist), a long non-coding RNA driving XCI, were detectable in the leukocytes of FD female carriers. Methods: We tested the XCI pattern in leukocytes on 33 consecutive females carrying pathogenic GLA variants. Disease severity was defined using the Mainz Severity Score Index (MSSI). Xist levels in leukocytes were assessed by real-time PCR and compared to the levels of 22 controls. Results: XCI was obtained for 31 female patients, finding 16 skewed (51.6%) individuals. Global MSSI did not differ in skewed vs. non-skewed FD carriers. In skewed FD females, the renal function and mean cardiologic MSSI subscore were significantly worse, and systemic arterial hypertension was more frequent. Xist levels detected in leukocytes were similar between female patients and controls, and did not differ by phenotype or XCI status. Conclusions: A skewed XCI pattern in leukocytes may represent a prognostic biomarker of worse renal and cardiac outcomes in female FD carriers.

Role of Circulating X-Chromosome Inactivation and Xist as Biomarkers in Female Carriers of Fabry Disease