Diminishing evidence for torsinA-positive neuronal inclusions in DYT1 dystonia

DYT1 dystonia, an early onset generalized dystonia, also known as Oppenheim’s dystonia, is an inherited isolated dystonia characterized by progressive generalized muscle spasms and sustained postures leading to significant disability [1]. The disease is inherited in an autosomal dominant manner with incomplete penetrance (30–40 %) and typically presents in childhood [2]. Patients harbor a 3-bp (GAG) deletion in the coding region of the TOR1A gene on chromosome 9q34 that encodes the protein torsinA [3]. This deletion corresponds to loss of a single glutamate at amino acid residue 302 or 303 (torsinA ΔE) [4]. The function of wildtype torsinA has been speculative, but relatively recent studies have demonstrated its involvement in protein trafficking, quality control, secretion, and degradation (for review, see Dauer 2014 [5]). The pathogenic mechanism leading to disease as a result of this deletion is thought to likely involve disruption of sensorimotor circuit development and function [6]. Recent evidence also suggests striatal cholinergic dysfunction, or dysregulation, as a potential mechanism underlying the pathophysiology of DYT1 dystonia [7]. Various in vitro and transgenic animal models of DYT1 dystonia have demonstrated altered cell morphology and nuclear changes at the light microscopic level, including torsinA accumulation and torsinA-positive inclusions in the brainstem (see Dauer 2014 [5] and Oleas et al. 2013 [8] for review of cell culture and animal model findings, respectively). Contrary to findings in animal tissues, no consistent or specific histopathologic changes have been noted in postmortem neuropathologic studies of patients with DYT1 dystonia (Table 1). Subcellular changes (e.g., inclusions) in DYT1 brains have been described in a small human postmortem study [9], but their specificity remains controversial. That study reported the presence of perinuclear and intranuclear inclusion bodies and protein accumulation in neurons that were immunoreactive for torsinA and ubiquitin, and co-localized with choline acetyltransferase (ChAT) and a nuclear envelope marker, lamin A/C, in the midbrain and pontine reticular formation (pedunculopontine nucleus (PPN), cuneiform nucleus (CN), and periaqueductal grey (PAG)); these changes were notably absent in controls. A more recent study, however, failed to confirm the presence of immunoreactive inclusions in human DYT1 dystonia brain tissue (using antibodies to ubiquitin and p62) [10]. Additionally, two earlier studies failed to reveal inclusion bodies, aggregates, or aberrant staining for torsinA in DYT1 brains and in other dystonia (non-DYT1) cases [11, 12]. Here, we sought to analyze genetically confirmed DYT1 brain specimens with antibodies to torsinA, ubiquitin protein conjugate (UPC), and ChAT in an attempt to identify the previously reported intracellular immunoreactive protein inclusions/aggregates in the midbrain as well as in other cholinergic nuclei, including the striatum. Our study included six brain samples from DYT1 patients (mean age 83.0 ± 9.1 years; all female), procured from the University of Maryland Brain and Tissue Bank (BTB); demographic and autopsy data from four of our DYT1 subjects matched those reported previously [10] and most likely represent tissue from the same subjects. In our study, three patients were clinically symptomatic and the remaining were nonmanifesting carriers of the DYT1 mutation. Control brain tissue samples from seven subjects without clinical evidence of dystonia or other movement disorders were matched for age and sex (mean age 83.4 ± 8.0 years; all female). Formalin-fixed paraffin-embedded (FFPE) tissue * Correspondence: [email protected] Equal contributors Human Motor Control Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 10 Center Drive, Room 7D42, Bethesda, MD 20892, USA Full list of author information is available at the end of the article