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.
Dystonia is a neurological condition characterized by abnormal involuntary movements or postures owing to sustained or intermittent muscle contractions. Dystonia can be the manifesting neurological ...sign of many disorders, either in isolation (isolated dystonia) or with additional signs (combined dystonia). The main focus of this Primer is forms of isolated dystonia of idiopathic or genetic aetiology. These disorders differ in manifestations and severity but can affect all age groups and lead to substantial disability and impaired quality of life. The discovery of genes underlying the mendelian forms of isolated or combined dystonia has led to a better understanding of its pathophysiology. In some of the most common genetic dystonias, such as those caused by TOR1A, THAP1, GCH1 and KMT2B mutations, and idiopathic dystonia, these mechanisms include abnormalities in transcriptional regulation, striatal dopaminergic signalling and synaptic plasticity and a loss of inhibition at neuronal circuits. The diagnosis of dystonia is largely based on clinical signs, and the diagnosis and aetiological definition of this disorder remain a challenge. Effective symptomatic treatments with pharmacological therapy (anticholinergics), intramuscular botulinum toxin injection and deep brain stimulation are available; however, future research will hopefully lead to reliable biomarkers, better treatments and cure of this disorder.
VPS13 protein family members VPS13A through VPS13C have been associated with various recessive movement disorders. We describe the first disease association of rare recessive VPS13D variants ...including frameshift, missense, and partial duplication mutations with a novel complex, hyperkinetic neurological disorder. The clinical features include developmental delay, a childhood onset movement disorder (chorea, dystonia, or tremor), and progressive spastic ataxia or paraparesis. Characteristic brain magnetic resonance imaging shows basal ganglia or diffuse white matter T2 hyperintensities as seen in Leigh syndrome and choreoacanthocytosis. Muscle biopsy in 1 case showed mitochondrial aggregates and lipidosis, suggesting mitochondrial dysfunction. These findings underline the importance of the VPS13 complex in neurological diseases and a possible role in mitochondrial function. Ann Neurol 2018;83:1089–1095
Chorea presenting in childhood and adulthood encompasses several neurological disorders, both degenerative and nonprogressive, often with a genetic basis. In this review, we discuss how modern ...genomic technologies are expanding our knowledge of monogenic choreic syndromes and advancing our insight into the molecular mechanisms responsible for chorea.
A genome-wide association study in Huntington's disease identified genetic disease modifiers involved in controlling DNA repair mechanisms and stability of the HTT trinucleotide repeat expansion. Chorea is the cardinal feature of newly recognized genetic entities, ADCY5 and PDE10A-related choreas, with onset in infancy and childhood. A phenotypic overlap between chorea, ataxia, epilepsy, and neurodevelopmental disorders is becoming increasingly evident.
The differential diagnosis of genetic conditions presenting with chorea has considerably widened, permitting a molecular diagnosis and an improved prognostic definition in an expanding number of cases. The identification of Huntington's disease genetic modifiers and new chorea-causing gene mutations has allowed the initial recognition of converging molecular pathways underlying medium spiny neurons degeneration and dysregulation of normal development and activity of basal ganglia circuits. Signalling downstream of dopamine receptors and control of cAMP levels represent a very promising target for the development of new aetiology-based treatments for chorea and other hyperkinetic disorders.
Chorea is a hyperkinetic movement disorder resulting from dysfunction of striatal medium spiny neurons (MSNs), which form the main output projections from the basal ganglia. Here, we used whole-exome ...sequencing to unravel the underlying genetic cause in three unrelated individuals with a very similar and unique clinical presentation of childhood-onset chorea and characteristic brain MRI showing symmetrical bilateral striatal lesions. All individuals were identified to carry a de novo heterozygous mutation in PDE10A (c.898T>C p.Phe300Leu in two individuals and c.1000T>C p.Phe334Leu in one individual), encoding a phosphodiesterase highly and selectively present in MSNs. PDE10A contributes to the regulation of the intracellular levels of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Both substitutions affect highly conserved amino acids located in the regulatory GAF-B domain, which, by binding to cAMP, stimulates the activity of the PDE10A catalytic domain. In silico modeling showed that the altered residues are located deep in the binding pocket, where they are likely to alter cAMP binding properties. In vitro functional studies showed that neither substitution affects the basal PDE10A activity, but they severely disrupt the stimulatory effect mediated by cAMP binding to the GAF-B domain. The identification of PDE10A mutations as a cause of chorea further motivates the study of cAMP signaling in MSNs and highlights the crucial role of striatal cAMP signaling in the regulation of basal ganglia circuitry. Pharmacological modulation of this pathway could offer promising etiologically targeted treatments for chorea and other hyperkinetic movement disorders.
Purpose of Review
Hyperkinetic movement disorders can manifest alone or as part of complex phenotypes. In the era of next-generation sequencing (NGS), the list of monogenic complex movement disorders ...is rapidly growing. This review will explore the main features of these newly identified conditions.
Recent Findings
Mutations in
ADCY5
and
PDE10A
have been identified as important causes of childhood-onset dyskinesias and
KMT2B
mutations as one of the most frequent causes of complex dystonia in children. The delineation of the phenotypic spectrum associated with mutations in
ATP1A3
,
FOXG1
,
GNAO1
,
GRIN1
,
FRRS1L
, and
TBC1D24
is revealing an expanding genetic overlap between epileptic encephalopathies, developmental delay/intellectual disability, and hyperkinetic movement disorders,.
Summary
Thanks to NGS, the etiology of several complex hyperkinetic movement disorders has been elucidated. Importantly, NGS is changing the way clinicians diagnose these complex conditions. Shared molecular pathways, involved in early stages of brain development and normal synaptic transmission, underlie basal ganglia dysfunction, epilepsy, and other neurodevelopmental disorders.
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