Objective: To establish induced pluripotent stem cells (iPSCs) of affected and unaffected Mutation carriers to investigate disease mechanisms of THAP1 in dystonia.

Background: Mutations in the THAP1 (THAP domain containing, apoptosis associated protein 1) gene may cause a form of early-onset, generalized dystonia (DYT-THAP1, also known as DYT6). Of note, some mutation carriers remain unaffected throughout their life (reduced penetrance). THAP1 encodes a transcription factor and it has been suggested that THAP1 regulates its own expression and TOR1A expression. Of note, TOR1A is also mutated in some patients with dystonia (DYT-TOR1A, DYT1). However, little is known about the gene expression in human iPSCs. Therefore, this study aims to investigate the mRNA expression levels of THAP1 and TOR1A in iPSCs of 4 affected and 6 unaffected members from three different families carrying pathogenic THAP1 variants (p.Arg13His, p.Ser21Cys, p.Leu159fs180X).

Methods: Cultured skin fibroblasts were reprogrammed into iPSCs using Sendai virus. Two clones per patient were comprehensively characterized by testing for the mutation using Sanger sequencing, by expression analysis of four pluripotency markers using quantitative PCR and immunocytochemistry, and by their ability to differentiate into all three germ layers. Genomic rearrangements were excluded by single nucleotide polymorphism (SNP) array analysis. Expression of THAP1 and TOR1A was tested by quantitative PCR compared to 10 iPSC controls while ß-Actin served as a reference gene.

Results: We generated 2 iPSC lines each of 10 affected and unaffected members of three families carrying pathogenic THAP1 variants (p.Arg13His [4 lines], p.Ser21Cys [10 lines], p.Leu159fs180X [6 lines]). THAP1 expression was reduced for Arg13His and TOR1A expression in Arg13His and Leu159fs180X mutant cell lines compared to controls.

Conclusions: We report the generation and characterization of 20 lines from 10 human THAP1 iPSC lines as well as alterations in THAP1 and TOR1A expression in these cells. These stem cells can further serve as an ideal model to investigate the mechanism of reduced penetrance by transcriptomic analysis in affected and unaffected THAP1 mutation carriers on the stem cell and differentiated neuron level.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/generation-and-in-depth-characterization-of-induced-pluripotent-stem-cell-ipsc-lines-from-10-affected-and-unaffected-carriers-of-thap1-mutations/