# Reactivation of Human X-Linked Gene and Stable X-Chromosome Inactivation Observed in Generation and Differentiation of iPSCs from a Female Patient with HNRNPH2 Mutation

## TL;DR

This study shows how X-chromosome inactivation behaves in stem cells from a female patient with an X-linked disorder, offering insights for disease modeling.

## Contribution

The study reveals stable XCI patterns during iPSC reprogramming and differentiation in a patient with an HNRNPH2 mutation.

## Key findings

- 12 iPSC clones showed either mutant or wild-type HNRNPH2 allele expression due to XCR and random XCI.
- XCI patterns remained stable during long-term iPSC propagation and differentiation into germ layers and neural stem cells.
- Findings highlight the importance of clone selection for accurate disease modeling in X-linked disorders.

## Abstract

X chromosome inactivation (XCI) is a fundamental epigenetic process that balances X-linked gene expression between females and males by silencing one X chromosome in female cells. Variability or skewing of XCI can influence the clinical presentation of X-linked disorders. Bain type X-linked intellectual disability syndrome (MRXSB), caused by mutations in the X-linked HNRNPH2 gene, is characterized by intellectual disability, developmental delay, and neurological abnormalities. In female patients, XCI heterogeneity complicates disease modeling and therapeutic development. Induced pluripotent stem cells (iPSCs) offer a unique platform to study patient-specific disease mechanisms, but the dynamics of XCI during iPSC reprogramming, maintenance, and differentiation are not fully understood. In this study, we generated 12 iPSC clones from fibroblasts of a female MRXSB patient heterozygous for the HNRNPH2 c.340C > T mutation. Four clones expressed the mutant HNRNPH2 allele and eight expressed the wild-type allele, indicating X chromosome reactivation (XCR) followed by random XCI during reprogramming. Importantly, these XCI patterns remained stable during long-term iPSC propagation and subsequent differentiation into the three germ layers and neural stem cells. Our findings provide new insights into XCI and XCR dynamics in the context of X-linked neurodevelopmental disorders and emphasize the importance of careful clone selection for accurate disease modeling using iPSC-based approaches.