Biochemical and Cellular Analysis of Human Variants of the DYT1 Dystonia Protein, TorsinA/TOR1A

Abstract

Early-onset dystonia is associated with the deletion of one of a pair of glutamic acid residues (c.904_906delGAG/c.907_909delGAG; p.Glu302del/Glu303del; ΔE 302/303) near the carboxyl-terminus of torsinA, a member of the AAA+ protein family that localizes to the endoplasmic reticulum (ER) lumen and nuclear envelope (NE). This deletion commonly underlies early-onset DYT1 dystonia. While the role of the disease-causing mutation, torsinAΔE, has been established through genetic association studies, it is much less clear whether other rare human variants of torsinA are pathogenic. Two missense variations have been described in single patients; R288Q (c.863G>A; p.Arg288Gln; R288Q) identified in a patient with onset of severe generalized dystonia and myoclonus since infancy, and F205I (c.613T>A, p.Phe205Ile; F205I) in a psychiatric patient with late-onset focal dystonia. In this study, we have undertaken a series of analyses comparing the biochemical and cellular effects of these rare variants to torsinAΔE and wild-type (wt) torsinA in order to reveal whether there are common dysfunctional features. The results revealed that the variants, R288Q and F205I, are more similar in their properties to torsinAΔE protein than to torsinAwt. These findings provide functional evidence for the potential pathogenic nature of these rare sequence variants in the TOR1A gene, thus implicating these pathologies in the development of dystonia.

A rare variant in TOR1A exon 5 associated with isolated dystonia in southwestern Chinese

“…In addition to c.904_906delGAG, several missense variants (including R288Q [p.Arg288Gln; c.863G>A] and F205I [p.Phe205Ile, c.613T>A]) found in dystonia patients have been published. These 3 types of mutant proteins all show an increased tendency to dimerize as well as impaired processing and altered NE morphology . Another rare variant found in our patients (c.860C>A) is adjacent to R288Q, so if c.860C>A damages the protein, it will likely cause dystonia.…”

The Role of TOR1A Polymorphisms in Dystonia: A Systematic Review and Meta-Analysis

“…TOR1A protein, called TorsinA belongs to the family of the AAA+ ATPases that can be found in the endoplasmic reticulum and nuclear envelope of most cells [8] including cells of the central nervous system [1] and are associated with a variety of cellular activities [9]. The function of TorsinA and how TOR1A gene mutations lead to dystonia is poorly understood.…”

“…The function of TorsinA and how TOR1A gene mutations lead to dystonia is poorly understood. However, it seems that TorsinA is implicated in several molecular and cellular procedures, such as the interactions between cytoskeleton and membrane, important functions of the endoplasmic reticulum (reaction to stress, secretory pathway, protein degradation, neurites’ expansion) and of the nuclear envelope (membrane formation and cell migration) [1, 8]. …”

Mouse model of rare TOR1A variant found in sporadic focal dystonia impairs domains affected in DYT1 dystonia patients and animal models

“…Rare variants in the Tor1a gene, as well as other genes associated with dystonia, have been reported in cases of sporadic dystonias (Calakos et al, 2010; Dobričić et al, 2015; Dufke et al, 2014; Groen et al, 2015; Groen et al, 2014; Hettich et al, 2014; Kock et al, 2006; Kumar et al, 2014; Lohmann et al, 2012; Nibbeling et al, 2015; Saunders-Pullman et al, 2014; Vemula et al, 2014; Vulinovic et al, 2014; Zech et al, 2014; Ziegan et al, 2014), suggesting this as one potential genetic contribution to disease. However, obtaining formal genetic support, as in association studies, is fundamentally challenged when rare genetic events occur in rare disorders.…”

“…In prior work, we found that, similar to ΔE TorsinA, F205I TorsinA protein mislocalizes and forms inclusions when over-expressed in cultured cells, though not to as severe a degree (Calakos et al, 2010). Nery and colleagues further showed that the F205I variant disrupts ER function (Hettich et al, 2014). These observations suggest that the mutation may be pathophysiologically significant.…”