Intronic VNTRs downregulate expression of HSF1 and confer genetic risk of essential tremor

Essential tremor (ET) is a highly prevalent movement disorder characterized by high heritability. However, the genetic basis of this disease remains largely unknown. Understanding the genetic causes of ET is crucial for unravelling its pathogenesis and developing targeted therapies. In this study, we aimed to investigate tandem repeats in a Chinese cohort of ET pedigrees. To explore the genetic causes of ET, we enrolled 165 Chinese ET pedigrees and performed whole-exome sequencing as well as long-read sequencing within this cohort. Quantitative real-time PCR and western blot analyses were employed to assess HSF1 expression levels. Transgenic Drosophila model and induced pluripotent stem cells (iPSCs) were constructed to investigate the pathogenic role of HSF1 in ET. Our study identified the expanded variable number of tandem repeats (VNTRs) in intron 10 of HSF1. Long-read sequencing revealed two repeat configurations consisting of CCCCGCNCCGCCT and CCNCGCCT in these VNTR loci. Expanded VNTR alleles were highly enriched in ET-affected individuals, and the length of VNTRs was positively correlated with disease severity. We found the intronic repeat expansions downregulated HSF1 expression in affected individuals, indicating its loss-of-function in ET. Consistently, RNAi knockdown of HSF1 homolog in Drosophila led to leg and head shaking and age-dependent movement deficits, recapitulating the ET phenotype in the fly model. iPSCs derived from the ET-affected individual carrying expanded VNTRs in the HSF1 gene exhibited significantly reduced expression of HSF1 compared to control iPSCs. Bulk RNA-sequencing analysis of these iPSCs revealed that diminished HSF1 expression resulted in the downregulation of genes associated with GABAergic synapse function. In conclusion, our study suggests that impaired GABAergic signalling may play a critical role in the pathogenesis of HSF1-related ET. These findings provide new information on the aetiology of ET and highlight the role of HSF1 in human genetic disorders.