Mechanisms Of Dystonia Research Articles

Chapter 13 - Plasticity, genetics and epigenetics in dystonia: An update

Dystonia represents a group of movement disorders characterized by involuntary muscle contractions that result in abnormal posture and twisting movements. In the last 20 years several animal models have been generated, greatly improving our knowledge of the neural and molecular mechanism underlying this pathological condition, but the pathophysiology remains still poorly understood. In this review we will discuss recent genetic factors related to dystonia and the current understanding of synaptic plasticity alterations reported by both clinical and experimental research. We will also present recent evidence involving epigenetics mechanisms in dystonia.

Emerging and converging molecular mechanisms in dystonia.

Dystonia is a clinically, genetically, and biologically heterogeneous hyperkinetic movement disorder caused by the dysfunctional activity of neural circuits involved in motor control. Our understanding of the molecular mechanisms underlying dystonia pathogenesis has tremendously grown thanks to the accelerated discovery of genes associated with monogenic dystonias (DYT-genes). Genetic discoveries, together with the development of a growing number of cellular and animal models of genetic defects responsible for dystonia, are allowing the identification of several areas of functional convergence among the protein products of multiple DYT-genes. Furthermore, unexpected functional links are being discovered in the downstream pathogenic molecular mechanisms of DYT-genes that were thought to be unrelated based on their primary molecular functions. Examples of these advances are the recognition that multiple DYT-genes are involved in (1) endoplasmic reticulum function and regulation of the integrated stress response (ISR) through Eukaryotic initiation factor 2 alpha signaling; (2) gene transcription modulation during neurodevelopment; (3) pre-and post-synaptic nigrostriatal dopaminergic signaling; and (4) presynaptic neurotransmitter vesicle release. More recently, genetic defects in the endo-lysosomal and autophagy pathways have also been implicated in the molecular pathophysiology of dystonia, suggesting the existence of mechanistic overlap with other movement disorders, such as Parkinson's disease. Importantly, the recognition that multiple DYT-genes coalesce in shared biological pathways is a crucial advance in our understanding of dystonias and will aid in the development of more effective therapeutic strategies by targeting these convergent molecular pathways.

Bilateral polymicrogyria associated with dystonia: A new neurogenetic syndrome?

The clinical presentation of bilateral perisylvian polymicrogyria (PMG) is highly variable, including oromotor dysfunction, epilepsy, intellectual disability, and pyramidal signs. Extrapyramidal features are extremely rare. We present four apparently unrelated patients with a unique association of PMG with dystonia. The clinical, genetic, and radiologic features are described and possible mechanisms of dystonia are discussed. All patients were female and two were born to consanguineous families. All presented with early childhood onset dystonia. Other neurologic symptoms and signs classically seen in bilateral perisylvian PMG were observed, including oromotor dysfunction and speech abnormalities ranging from dysarthria to anarthria (4/4), pyramidal signs (3/4), hypotonia (3/4), postnatal microcephaly (1/4), and seizures (1/4). Neuroimaging showed a unique pattern of bilateral PMG with an infolded cortex originating primarily from the perisylvian region in three out of four patients. Whole exome sequencing was performed in two out of four patients and did not reveal pathogenic variants in known genes for cortical malformations or movement disorders. The dystonia seen in our patients is not described in bilateral PMG and suggests an underlying mechanism of impaired connectivity within the motor network or compromised cortical inhibition. The association of bilateral PMG with dystonia in our patients may represent a new neurogenetic disorder.

What can kinematic studies tell us about the mechanisms of dystonia?

Clinical movement disorders are classified by an algorithm implemented by a practising movement disorder specialist based on information extracted during the history and clinical examination of a patient. Most simply, dystonia, is a classifier which is reached when a predominant abnormality of posture is noted. In this chapter we summarize studies that have used a variety of techniques to probe beyond the clinical examination and study kinematic features experimentally. We also outline our experimental work in DYT1 dystonia, a group of patients that share a genetically homogenous etiology and can be considered a prototypical dystonic disorder. Our results build on previous studies, confirming that motor variability on a trial-by-trial basis is selectively increased and provide evidence that increases in variability are negatively related to forms of motor learning essential for healthy motor control. Potential neural correlates of increased motor variability are discussed and the implications such work has for the rehabilitation of patients with dystonia are also highlighted.

Dystonia: hopes for a better diagnosis and a treatment with long-lasting effect

Dystonias represent a group of heterogeneous neurological conditions characterized by sustained simultaneous co-contraction of agonist and antagonist muscles in one or more sites of the body. The resultant repetitive movements and abnormal postures can affect gait and execution of voluntary movements. The pathophysiological mechanisms of dystonia remain to be fully elucidated. Not long ago, dystonia was commonly considered a manifestation of psychiatric disturbances and it has taken more than 40 years to recognize that dystonic movements originate from dysfunction within the basal ganglia circuitry. Findings from neuroimaging studies and physiological investigations clearly indicate that dystonia is associated with reduced inhibitory basal ganglia output, failure of cortical inhibition, abnormal sensorimotor integration, and maladaptive plasticity (Hallett, 2006). Over the last 20 years, many imaging studies using 18F-FDG PET, H2[15O] PET and functional MRI have been performed in patients with different types of dystonia and have revealed widespread changes in cortical and subcortical activity, both at rest and during execution of motor tasks (van Eimeren et al ., 2006; Neychev et al ., 2011). Patients with primary dystonia caused by mutations in the DYT1 and DYT6 genes and asymptomatic gene carriers of these mutations, show an abnormal resting metabolic brain network, consisting of hypermetabolism of the basal ganglia, supplementary motor area and the cerebellum (Trost et al ., 2002). Activation studies …

Current Concepts on the Mechanisms of Dystonia and the Beneficial Effects of Deep Brain Stimulation

The application of lesioning procedures in the basal ganglia and, more recently, of deep brain stimulation (DBS) has revolutionalized dystonia treatment. However, our understanding of the mechanism of action of DBS is only minimal. This is largely due to a rudimentary understanding of dystonia pathophysiology itself, which in turn reflects an insufficient understanding of the functional significance of the cortico-striato-pallido-thalamocortical loops. The initial dystonia pathophysiology concept was one of changes in oscillation rate. Soon, it was realized that not only rate but also the pattern of basal ganglia activity is crucial in the etiology of the disease. The observations of altered somatosensory responsiveness and cortical neuroplasticity, along with the vast array of clinical phenotypes, imply the need for a wholistic neuronal pathophysiology model; one in which an underlying defect of basal ganglia function results in increased cortical excitability, misprocessing of sensory feedback, aberrant cortical plasticity, and ultimately clinical dystonia. This unified dystonia pathophysiology model, although simplistic, may provide the scaffold on which all incoming research and clinical data becomes united in a meaningful and practical way. In light of this model, the dramatic response of some forms of dystonia to pallidal stimulation, the time latency for the beneficial effect and even the presence of non-responders may be explained. Additionally, it may help in developing a rationale for more efficacious DBS programming, better selection of the timing of surgery, and more successful identification of those candidates that are most likely to respond to DBS.

Advances in Our Understanding of Dystonia - Pathophysiology and Treatment Options

Although the pathophysiology of dystonia remains incompletely understood, advances in two major areas of research over the past two decades have led to important insights into the mechanisms of dystonia. First, with the identification of dystonia genes, investigations using cellular and animal models of dystonia have become possible. Second, advances in functional neuroimaging have led to the possibility of identification of distinct functional, anatomical and neurochemical abnormalities in dystonia patients. Dystonia is currently conceptualised as a neurofunctional disorder characterised by alterations at various levels and multiple points along the sensorimotor circuit. There are multiple causes of these disruptions, and lesions along different points in interconnected pathways can yield similar motor dysfunction. The existence of dystonia endophenotypes in genetic forms of dystonia suggests that it may be a ‘second hit’ disorder, in which genetically predisposed brains can be thrown into an unbalanced dystonic state by environmental or genetic factors. Ultimately, a more complete understanding of the pathophysiology of dystonia should lead to better, more rational, targeted therapies.

Advances in Our Understanding of Dystonia—Pathophysiology and Treatment Options

Although the pathophysiology of dystonia remains incompletely understood, advances in two major areas of research over the past two decades have led to important insights into the mechanisms of dystonia. First, with the identification of dystonia genes, investigations using cellular and animal models of dystonia have become possible. Second, advances in functional neuroimaging have led to the possibility of identification of distinct functional, anatomic, and neurochemical abnormalities in dystonia patients. Dystonia is currently conceptualized as a neurofunctional disorder characterized by alterations at various levels and multiple points along the sensorimotor circuit. There are multiple causes of these disruptions, and lesions along different points in interconnected pathways can yield similar motor dysfunction. The existence of dystonia endophenotypes in genetic forms of dystonia suggests that it may be a ‘second hit’ disorder, in which genetically predisposed brains can be thrown into an unbalanced dystonic state by environmental or genetic factors. Ultimately, a more complete understanding of the pathophysiology of dystonia should lead to better, more rational, targeted therapies.

Clinical improvement of secondary focal limb dystonia in neurodegenerative disease following a five-day lidocaine infusion: A case report

Dystonia associated with neurodegenerative disease has minimal effective treatment options and can be devastating to a patient's ability to perform tasks of daily living. We present a case of a 55 year-old man who had progressive symptoms of an atypical asymmetric parkinsonian neurodegenerative disease. This patient presented with a dystonic left upper extremity that was refractory to treatment. In an attempt to treat worsening pain associated with the dystonia, he was given a five-day lidocaine infusion for associated pain and within 24 h had improvement in mobility of his dystonic extremity. Dystonia was measured by the Burke–Fahn–Marsden (BFM) dystonia rating and disability scales on hospital day five and at an eight week follow up visit. These scores were compared with scores derived from his previous pre-treatment neurologic examination. The BFM dystonia scale score was initially 16 and improved to 12 on both immediate post-treatment and eight-week follow-up. The BFM disability score improved from 16 to 6 post treatment and to 8 on follow-up appointment. Most importantly, the patient could feed and dress himself for the first time in several years. No adverse events of treatment were encountered. Treatment effect lasted three months with a slow return to baseline motor function. This case report raises interesting questions regarding the mechanism of dystonia in neurodegenerative disease and suggests the afferent sensory system as a potential target for therapeutics.

Dystonia and parkinsonism

Parkinsonism and dystonia may coexist in a number of neurodegenerative, genetic, toxic, and metabolic disorders and as a result of structural lesions in the basal ganglia. Parkinson's disease (PD) and the ‘Parkinson-plus’ syndromes (PPS) account for the majority of patients with the parkinsonism–dystonia combination. Dystonia, particularly when it involves the foot, may be the presenting sign of PD or PPS and these disorders should be suspected when adults present with isolated foot dystonia. Young age, female gender, and long disease duration are risk factors for PD-related dystonia, but dystonia in patients with PD is usually related to levodopa therapy. The mechanism of dystonia in PD is not well understood and the management is often challenging because levodopa and other dopaminergic agents may either improve or worsen dystonia. Other therapeutic strategies include oral medications (baclofen, anticholinergics and benzodiazepines), local injections of botulinum toxin, intrathecal baclofen, and surgical lesions or high frequency stimulation of the thalamus, globus pallidus, or subthalamus.

SS-8-7 Afferent mechanisms in dystonia

SS-8-7 Afferent mechanisms in dystonia