Dystonia: opportunities to gain insights into underlying pathophysiological mechanisms

Dystonia is one of the most common movement disorders, a core component of the isolated and combined dystonias as well as contributing to the motor phenotype of several neurodegenerative movement disorders, such as Parkinson’s disease and Huntington’s disease. In spite of this, the pathophysiological mechanisms underlying dystonia remain poorly understood with the current thinking centered on a circuit-based disorder, with altered synaptic plasticity impacting higher neuronal circuits and networks. In this review, we discuss three publications with distinct approaches in attempting to elucidate these mechanisms. These articles also highlight how the combination of gene discovery, cellular assays, and systems-based analysis can each contribute to building an understanding of complex disorders

Idiopathic rapid eye movement sleep behaviour disorder: a potential gateway to the development of disease-modifying treatments in neurodegenerative disorders

Idiopathic rapid eye movement (REM) sleep behavioural disorder (RBD) is classified as one of the REM parasomnias with clinical characteristics including unpleasant dreams, acting out of dreams, and loss of the typical muscle atonia during the REM phase of sleep. Other associated clinical features include olfactory loss, dysautonomia, colour vision impairment and subtle Parkinsonian signs. RBD has been shown to predict development of an alpha-synucleinopathy in 20–45 % of patients within 5 years, and up to 92 % within 14 years post-diagnosis. Hence, this disorder provides a potential opportunity for understanding the prodromal stages of the synucleinopathies and exploring efficacy of potential neuroprotective agents

Benign Hereditary Chorea: An Update

Benign hereditary chorea (BHC) is a childhood-onset, hyperkinetic movement disorder normally with little progression of motor symptoms into adult life. The disorder is caused by mutations to the NKX2.1 (TITF1) gene and also forms part of the “brain–lung–thyroid syndrome”, in which additional developmental abnormalities of lung and thyroid tissue are observed. In this review, we summarize the main clinical findings in “classical” BHC syndrome and discuss more recently reported atypical features, including non-choreiform movement phenotypes. We highlight additional non-motor characteristics such as cognitive impairment and psychiatric symptoms, while discussing the evidence for BHC as a developmental disorder involving impaired neural migration and other multisystem developmental abnormalities. Finally, we will discuss the efficacy of available therapies in both affected pediatric and adult cohorts. Delineation of the BHC disease spectrum will no doubt expand our understanding of this disorder, facilitating better targeting of genetic testing and establish a framework for future clinical trials

Clinical and genetic investigation of the epsilon-sarcoglycan complex in neurologic and psychiatric disease

Myoclonus Dystonia Syndrome is a childhood onset hyperkinetic movement disorder characterised by alcohol responsive upper body myoclonus and dystonia. A proportion of cases are due to mutations in the maternally imprinted SGCE gene, which encodes the transmembrane epsilon-sarcoglycan protein. Previous studies suggest an increased rate of psychiatric disorders in those with SGCE mutations. This study aimed to establish a cohort of myoclonus dystonia syndrome patients, identify the rate and type of SGCE mutations, determine differences in motor characteristics between mutation positive and negative cases and whether psychiatric disorders form part of the disease phenotype. Eighty-nine probands with clinically suspected MDS were recruited. Information regarding onset and distribution of motor symptoms was collected via systematic questionnaires and video taped examination. SGCE was analysed using direct sequencing and for copy number variants. Psychiatric symptoms were assessed using systematic and standardised questionnaires and compared to a disability-matched, alcohol responsive tremor control group. Nineteen (21%) probands had an SGCE mutation. All had evidence of upper body predominant myoclonus and dystonia during their disease course. Five had contiguous gene deletions ranging from 0.7 to 2.3Mb in size with distinctive clinical features. Recruitment of family members increased the affected SGCE mutation positive group to 27 of whom 21 (77%) had psychiatric symptoms. Obsessive-Compulsive Disorder was eight times more likely (p<0.001) in mutation positive cases, compulsivity being the predominant feature (p<0.001). Generalized Anxiety Disorder (p=0.003) and alcohol dependence (p=0.02) were five times more likely in cases than tremor controls. Overall, SGCE mutations are associated with a narrow clinical and specific psychiatric phenotype. The presence of myoclonus, dystonia, age at onset ≤10 years and a positive family history of the disorder are the strongest predictors of an SGCE mutation. SGCE mutations are likely to have a pleiotropic effect in causing both motor and specific psychiatric symptoms

Internet-based cognitive behavioural therapy programme as an intervention for people diagnosed with adult-onset, focal, isolated, idiopathic cervical dystonia: a feasibility study protocol

Background Dystonia is one of the most common forms of movement disorder, caused by the co-contraction of antagonistic muscles, leading to abnormal postures and considerable disability. Non-motor symptoms, notably psychiatric disorders, are well recognised comorbid features of the disorder. However, there is no standardised model for the management of these symptoms in dystonia, with them frequently going undiagnosed and untreated. An internet-based cognitive behavioural therapy programme may provide a future model of care that also maximises available resources. Methods This study represents a two-armed randomised feasibility trail, aiming to recruit a total of 20 participants with a diagnosis of adult-onset primary focal cervical dystonia. Participants will be recruited from the Global Myoclonus Dystonia Registry and Dystonia Non-Motor Symptom Study (conducted at Cardiff University) based on presence of moderate symptoms of anxiety/depression as indicated by standardised questionnaires. All participants will undergo assessment at baseline, 3 and 6 months, with this including questionnaires for assessment of non-motor symptoms and clinical assessment of motor symptom severity. Participants will be randomised to either the control (n = 10) or treatment (n = 10) groups. The treatment group will be asked to complete one session of the online CBT program a week, for 8 weeks. The primary outcome measure will be the engagement of participants with the programme, with secondary outcomes of non-motor and motor symptom scores. Discussion Promising results have been shown using face-to-face cognitive behavioural therapy to reduce levels of anxiety and depression in individuals with a diagnosis of dystonia. However, no studies to date have sought to determine the feasibility of an internet-delivered cognitive behavioural therapy programme. A number of effective internet-based programmes have been developed that combat anxiety and depression in the general population, suggesting the potential for its effectiveness in cervical dystonia patients. Success with this study would significantly impact the clinical care delivery for patients with cervical dystonia, as well as widening potential access to effective treatment

Nitrous oxide misuse and vitamin B12 deficiency

A 36-year-old man presented to hospital with a 5-week history of ascending limb paraesthesiae and balance difficulties. He had no medical or travel history of note, but admitted habitual nitrous oxide (N2O) inhalation. Neurological examination revealed a sensory ataxia with pseudoathetosis in the upper limbs and reduced vibration sensation to the hips bilaterally. Significant investigation results included a low serum vitamin B12 concentration, mild macrocytosis and raised serum homocysteine concentration. T2 MRI of the spinal cord demonstrated increased signal extending from C1 to T11 in keeping with a longitudinal myelitis. The patient was diagnosed with a myeloneuropathy secondary to vitamin B12 deficiency, resulting from heavy N2O inhalation. He was treated with intramuscular vitamin B12 injections and received regular physiotherapy. At discharge, he was able to mobilise short distances with the aid of a zimmer frame, and was independently mobile 8 weeks later

A review of psychiatric co-morbidity described in genetic and immune mediated movement disorders

Psychiatric symptoms are an increasingly recognised feature of movement disorders. Recent identification of causative genes and autoantibodies has allowed detailed analysis of aetiologically homogenous subgroups, thereby enabling determination of the spectrum of psychiatric symptoms in these disorders. This review evaluates the incidence and type of psychiatric symptoms encountered in patients with movement disorders. A broad spectrum of psychiatric symptoms was identified across all subtypes of movement disorder, with depression, generalised anxiety disorder and obsessive-compulsive disorder being most common. Psychosis, schizophrenia and attention deficit hyperactivity disorder were also identified, with the psychiatric symptoms often predating onset of the motor disorder. The high incidence of psychiatric symptoms across such a wide range of movement disorders suggests a degree of common or overlapping pathogenic mechanisms. Our review demonstrates the need for increased clinical awareness of such co-morbidities, which should facilitate early neuropsychiatric intervention and allied specialist treatment for patients

Medical management of myoclonus-dystonia and implications for underlying pathophysiology

Myoclonus-dystonia is an early onset genetic disorder characterised by subcortical myoclonus and less prominent dystonia. Its primary causative gene is the epsilonsarcoglycan gene but the syndrome of “myoclonic dystonia” has been shown to be a heterogeneous group of genetic disorders. The underlying pathophysiology of myoclonus-dystonia is incompletely understood, although it may relate to dysfunction of striatal monoamine neurotransmission or disruption of cerebellothalamic networks (possibly via a GABAergic deficit of Purkinje cells). A broad range of oral medical therapies have been used in the treatment of myoclonus-dystonia with a varying response, and limited data relating to efficacy and tolerability, yet this condition responds dramatically to alcohol. Few well conducted randomized controlled trials have been undertaken leading to an empirical ad hoc approach for many patients. We review the current evidence for pharmacological therapies in myoclonus-dystonia, discuss implications for underlying pathogenesis of the condition and propose a treatment algorithm for these patients

Wearable movement-tracking data identify Parkinson's disease years before clinical diagnosis

Parkinson’s disease is a progressive neurodegenerative movement disorder with a long latent phase and currently no disease-modifying treatments. Reliable predictive biomarkers that could transform efforts to develop neuroprotective treatments remain to be identified. Using UK Biobank, we investigated the predictive value of accelerometry in identifying prodromal Parkinson’s disease in the general population and compared this digital biomarker with models based on genetics, lifestyle, blood biochemistry or prodromal symptoms data. Machine learning models trained using accelerometry data achieved better test performance in distinguishing both clinically diagnosed Parkinson’s disease (n = 153) (area under precision recall curve (AUPRC) 0.14 ± 0.04) and prodromal Parkinson’s disease (n = 113) up to 7 years pre-diagnosis (AUPRC 0.07 ± 0.03) from the general population (n = 33,009) compared with all other modalities tested (genetics: AUPRC = 0.01 ± 0.00, P = 2.2 × 10−3; lifestyle: AUPRC = 0.03 ± 0.04, P = 2.5 × 10−3; blood biochemistry: AUPRC = 0.01 ± 0.00, P = 4.1 × 10−3; prodromal signs: AUPRC = 0.01 ± 0.00, P = 3.6 × 10−3). Accelerometry is a potentially important, low-cost screening tool for determining people at risk of developing Parkinson’s disease and identifying participants for clinical trials of neuroprotective treatments

Sleep disturbance in movement disorders:insights, treatments and challenges

Sleep and circadian rhythm disturbances are central features of many movement disorders, exacerbating motor and non-motor symptoms and impairing quality of life. Understanding these disturbances to sleep is clinically important and may further our understanding of the underlying movement disorder. This review evaluates the current anatomical and neurochemical understanding of normal sleep and the recognised primary sleep disorders. In addition, we undertook a systematic review of the evidence for disruption to sleep across multiple movement disorders. Rapid eye movement sleep behaviour disorder has emerged as the most reliable prodromal biomarker for the alpha synucleinopathies, including Parkinson’s disease and multiple system atrophy, often preceding motor symptom onset by several years. Abnormal sleep has also been described for many other movement disorders, but further evidence is needed to determine whether this is a primary or secondary phenotypic component of the underlying condition. Medication used in the treatment of motor symptoms also affects sleep and can aggravate or cause certain sleep disorders. Within the context of movement disorders, there is also some suggestion of a shared underlying mechanism for motor and sleep pathophysiology, with evidence implicating thalamic and brainstem structures and monoaminergic neurotransmission. This review highlights the need for an understanding of normal and abnormal sleep within the movement disorder clinic, an ability to screen for specific causes of poor sleep and to treat sleep disturbance to improve quality of life. Key sleep disorders also act as important biomarkers and have implications in diagnosis, prognosis and the development of future therapies