Dystonia update

Allan-Herndon-Dudley-Syndrome: Considerations about the Brain Phenotype with Implications for Treatment Strategies

Despite its first description more than 75 years ago, effective treatment for "Allan-Herndon-Dudley-Syndrome (AHDS)", an X-linked thyroid hormone transporter defect, is unavailable. Mutations in the SLC16A2 gene have been discovered to be causative for AHDS in 2004, but a comprehensive understanding of the function of the encoded protein, monocarboxylate transporter 8 (MCT8), is incomplete. Patients with AHDS suffer from neurodevelopmental delay, as well as extrapyramidal (dystonia, chorea, athetosis), pyramidal (spasticity), and cerebellar symptoms (ataxia). This suggests an affection of the pyramidal tracts, basal ganglia, and cerebellum, most likely already during fetal brain development. The function of other brain areas relevant for mood, behavior, and vigilance seems to be intact. An optimal treatment strategy should thus aim to deliver T3 to these relevant structures at the correct time points during development. A potential therapeutic strategy meeting these needs might be the delivery of T3 via a "Trojan horse mechanism" by which T3 is delivered into target cells by a thyroid hormone transporter independent T3 internalization.

Neurodegeneration in an adolescent with Sjogren-Larsson syndrome: a decade-long follow-up case report

BACKGROUND

Sjogren-Larsson syndrome is a hereditary neurocutaneous syndrome that is non-progressive in nature. Although neuroregression has been reported in seizure-prone preschool children requiring anti-epileptic treatment, teenage-onset dystonia precipitating neurodegeneration without any immediate causal events has yet to be reported.

CASE PRESENTATION

We describe a young woman with spastic diplegia and intellectual disability who began to show progressive neurological deterioration from 12 years of age, with the onset of dystonia and tremor. She was initially diagnosed with spastic cerebral palsy and periventricular leukomalacia based on brain magnetic resonance imaging. Follow-up brain imaging from 13 years of age did not reveal apparent changes, though abnormal electroencephalographic findings occurred in parallel with her decline in motor function. By 19 years of age, she had developed dysphagia and became completely dependent on others for most activities of daily living. Ultimately, whole-exome sequencing revealed a heterozygous compound mutation in the ALDH3A2 gene that corresponds to Sjogren-Larsson syndrome: an exon 9 deletion (1291-1292delAA) from the mother and an exon 5 splicing mutation (798 + 1delG) from the father. Neuroregression has been reported in preschool children after seizures requiring treatment, though our patient did not experience any immediate causal events. This report summarizes the clinical, radiologic, and electrophysiological findings observed over a decade concurrent with neurological deterioration after the onset of dystonia and tremor at the age of developmental ceiling in Sjogren-Larsson syndrome.

CONCLUSIONS

In addition to the influence of additive variants or other environmental factors, accumulation of metabolites due to defective fatty aldehyde dehydrogenase is a potential pathomechanism of neurodegeneration in this patient. Neurological deterioration may be a presentation that is unnoticed in Sjogren-Larsson syndrome due to the rarity of the disease. This report highlights a unique clinical feature of Sjogren-Larsson syndrome with progressive neurodegeneration associated with dystonia and tremor.

Therapeutic challenges in dystonia

Because dystonia can vary in clinical presentation and etiology, proper diagnosis and classification of these disorders are important in making therapeutic decisions. In primary dystonia, treatment is generally geared toward alleviating symptoms rather than curing the underlying condition, therefore severity of contractions, pain, and functional and social impact are also factors to consider in determining if and how to initiate therapy. On the other hand, if a secondary cause is identified, then it is often appropriate to direct treatment toward the underlying disorder. Treatment options include physical and occupational therapy, oral medications, botulinum toxin, and surgery. This article briefly reviews the clinical features, pathophysiology, and classification of dystonia before reviewing current therapeutic options.

Familial leukoencephalopathy with slowly progressive dystonia and ataxia

We describe two siblings with childhood onset, slowly progressive generalized dystonia and cerebellar signs. Brain neuroimaging revealed white matter abnormalities compatible with a neuronal degenerative disorder. An extensive evaluation for mitochondrial, metabolic, autoimmune or other known neurodegenerative disorders did not reveal the etiology of the disease. During a three-year follow-up other neurological signs appeared, but progression was very slow. We believe that our patients have a new type of a leukoencephalopathy with slowly progressive dystonia and cerebellar signs.

Microstructural white matter changes in primary torsion dystonia

Primary torsion dystonia (PTD) has been conceptualized as a disorder of the basal ganglia. However, recent data suggest a widespread pathology involving motor control pathways. In this report, we explored whether PTD is associated with abnormal anatomical connectivity within motor control pathways. We used diffusion tensor magnetic resonance imaging (DT-MRI) to assess the microstructure of white matter. We found that fractional anisotropy, a measure of axonal integrity and coherence, was significantly reduced in PTD patients in the pontine brainstem in the vicinity of the left superior cerebellar peduncle and bilaterally in the white matter of the sensorimotor region. Our data thus support the possibility of a disturbance in cerebello-thalamo-cortical pathways as a cause of the clinical manifestations of PTD.

Dystonia

Dystonia is a disorder of involuntary sustained muscle contractions. It is commonly classified by age of onset, distribution of involved body regions, and etiology. The pathophysiolgy of this condition is complex and imperfectly understood. This article reviews the epidemiology, genetics, clinical features, and approach to diagnosis and treatment of dystonia.

Symptomatic segmental dystonia from a cavernous angioma in the centrum semiovale

We describe a 68 year-old Chinese man who presented with segmental dystonia involving the neck and right upper limb, which was exacerbated with action. EEG and MRI of the cervical spine were unremarkable, but MRI of the brain revealed a small cavernous angioma measuring one centimeter in diameter in the left centrum semiovale. The dystonia was ameliorated but not abolished with trihexyphenidyl. Arteriovenous malformations have been described to cause movement disorders, but dystonia has not previously been reported in association with cavernous angiomas. A search of the literature revealed one report of a patient with chorea arising from a cavernous angioma. This interesting case illustrates how an uncomplicated cavernous angioma can rarely cause segmental dystonia and highlights the importance of neuroimaging in patients with late-onset movement disorders.

The gene for paroxysmal non-kinesigenic dyskinesia encodes an enzyme in a stress response pathway

Paroxysmal non-kinesigenic dyskinesia (PNKD) is characterized by spontaneous hyperkinetic attacks that are precipitated by alcohol, coffee, stress and fatigue. We report mutations in the myofibrillogenesis regulator 1 (MR-1) gene causing PNKD in 50 individuals from eight families. The mutations cause changes (Ala to Val) in the N-terminal region of two MR-1 isoforms. The MR-1L isoform is specifically expressed in brain and is localized to the cell membrane while the MR-1S isoform is ubiquitously expressed and shows diffuse cytoplasmic and nuclear localization. Bioinformatic analysis reveals that the MR-1 gene is homologous to the hydroxyacylglutathione hydrolase (HAGH) gene. HAGH functions in a pathway to detoxify methylglyoxal, a compound present in coffee and alcoholic beverages and produced as a by-product of oxidative stress. Our results suggest a mechanism whereby alcohol, coffee and stress may act as precipitants of attacks in PNKD. Stress response pathways will be important areas for elucidation of episodic disease genetics where stress is a common precipitant of many common disorders like epilepsy, migraine and cardiac arrhythmias.

Mouvements anormaux de l’enfant : nouveautés thérapeutiques

Abnormal movements are not uncommon in childhood. Due to the severity of the abnormal movements or to the functional disability, a medical treatment is often required; the wide range of available pharmacological molecules and the absence of therapeutic consensus highlight the limited efficacy of the medical treatment on dystonic or athetoid movements, or severe tic disorders. The recent identification of the enzymatic defect implicated in metabolic diseases led to the development of specific treatment for newly recognized disorders, with more or less interesting results (creatine ou biotine supplementation). Recent progress in functional neurosurgery opened new fields in the treatment of movement disorders. Intrathecal baclofen was proved effective in the treatment of secondary dystonia, especially in patients with cerebral palsy. Deep brain stimulation is now an established therapy for patients with a generalized dystonic syndrome. Given the successful results of pallidal stimulation in dystonia, the indication of this procedure has been discussed in other types of abnormal movements.