Pitfalls of X-chromosome inactivation testing in females with Fabry disease

Am J Med Genet A. 2022 Jul;188(7):1979-1989. doi: 10.1002/ajmg.a.62728.

PMID: 35338595

Martin Řeboun, Jakub Sikora, Martin Magner

Highlights: In this study, it is aimed to determine pitfalls of XCI testing in a cohort of 35 female Fabry disease (FD) patients.

Abstract

Background: A lysosomal storage disorder called Fabry disease (FD) is caused by mutations in the GLA gene, which codes for alpha-galactosidase A (AGAL). It is yet unknown how X-chromosome inactivation (XCI) affects the phenotype of female FD patients.

Objective and methods: In this study, a cohort of 35 female FD patients was used to identify the pitfalls of XCI testing. Two methylation-based and two allele-specific expression tests were used to evaluate XCI.

Results: Although there was considerable variation amongst the four assays, the results correlated. Three patients had crossing-over that was discovered by GLA transcript analysis, and three of the four studied null alleles showed signs of mRNA instability. Reduced mRNA stability or the kind of mutation had no effect on the correlation between AGAL activity and the XCI pattern. Consequently, in patients with unstable GLA alleles, AGAL activity may aid in the detection of crossing-over. In six cases, tissue-specific XCI patterns and aging-related alterations were noted.

Conclusion: To avoid misinterpretation of XCI results in female FD patients we demonstrate that (i) the use of multiple XCI assays together produces more accurate results and reduces potential biases; (ii) the correlation of XCI to GLA expression and AGAL activity facilitates the identification of cross-over events; and (iii) age- and tissue-related XCI specificities of XCI patterning should be considered.

Keywords: Fabry disease heterozygotes, GLA transcript expression, X chromosome inactivation assay, alpha-galactosidase A activity