Rapid-onset dystonia-parkinsonism with ATP1A3 mutation and left lower limb paroxysmal dystonia

ATP1A3 mutation in rapid-onset dystonia parkinsonism: New data and genotype-phenotype correlation analysis

Background

Rapid-onset dystonia parkinsonism (RDP) is a rare disease caused by ATP1A3 mutation with considerable clinical heterogeneity. Increased knowledge of RDP could be beneficial in its early diagnosis and treatment.

Objective

This study aimed to summarize the gene mutation spectrum of ATP1A3 associated with RDP, and to explore the correlation of ATP1A3 variants with RDP clinical phenotypes.

Methods

In this study, we reported two RDP patients from a family with a novel inherited ATP1A3 variant. Then, we reviewed and analyzed the available literature in English focused on ATP1A3-causative RDP. A total of 35 articles covering 15 families (59 patients) and 36 sporadic RDP cases were included in our analysis.

Results

The variant A813V (2438C>T) in ATP1A3 found in our cases was a novel mutant. Delays in diagnosis were common, with a mean delay time of 14 years. ATP1A3 had distinct RDP-related mutation hotspots, which consisted of exon8, 14, 17, and 18, and the most frequently occurring variants were T613M and I578S. Approximately 74.5% of patients have specific triggers before disease onset, and 82.1% of RDPs have stable symptoms within 1 month. The incidence rates of dystonia and bradykinesia are 100 and 88.1%, respectively. The onset site varied and exhibited a rostrocaudal gradient distribution pattern in 45% of patients with RDP. Approximately 63.6% of patients had mild improvement after receiving comprehensive interventions, especially in gait disturbance amelioration.

Conclusion

In patients with acute and unexplained dystonia or bradykinesia, gene screening on ATP1A3 should be timely performed. When a diagnosis has been made, treatments that may be effective are to be attempted. Our study would be helpful for the early diagnosis and treatment of ATP1T3-related RDP.

Parkinsonism and dystonia: Clinical spectrum and diagnostic clues

The links between the two archetypical basal ganglia disorders, dystonia and parkinsonism, are manifold and stem from clinical observations, imaging studies, animal models and genetics. The combination of both, i.e. the syndrome of dystonia-parkinsonism, is not uncommonly seen in movement disorders clinics and has a myriad of different underlying aetiologies, upon which treatment and prognosis depend. Based on a comprehensive literature review, we delineate the clinical spectrum of disorders presenting with dystonia-parkinsonism. The clinical approach depends primarily on the age at onset, associated neurological or systemic symptoms and neuroimaging. The tempo of disease progression, and the response to L-dopa are further important clues to tailor diagnostic approaches that may encompass dopamine transporter imaging, CSF analysis and, last but not least, genetic testing. Later in life, sporadic neurodegenerative conditions are the most frequent cause, but the younger the patient, the more likely the cause is unravelled by the recent advances of molecular genetics that are focus of this review. Here, knowledge of the associated phenotypic spectrum is key to guide genetic testing and interpretation of test results. This article is part of the Special Issue "Parkinsonism across the spectrum of movement disorders and beyond" edited by Joseph Jankovic, Daniel D. Truong and Matteo Bologna.

Genetic updates on paroxysmal dyskinesias

The paroxysmal dyskinesias are a diverse group of genetic disorders that manifest as episodic movements, with specific triggers, attack frequency, and duration. With recent advances in genetic sequencing, the number of genetic variants associated with paroxysmal dyskinesia has dramatically increased, and it is now evident that there is significant genotype-phenotype overlap, reduced (or incomplete) penetrance, and phenotypic variability. In addition, a variety of genetic conditions can present with paroxysmal dyskinesia as the initial symptom. This review will cover the 34 genes implicated to date and propose a diagnostic workflow featuring judicious use of whole-exome or -genome sequencing. The goal of this review is to provide a common understanding of paroxysmal dyskinesias so basic scientists, geneticists, and clinicians can collaborate effectively to provide diagnoses and treatments for patients.

ATP1A3-Related Disorders: An Ever-Expanding Clinical Spectrum

The Na+/K+ ATPases are Sodium-Potassium exchanging pumps, with a heteromeric α-β-γ protein complex. The α3 isoform is required as a rescue pump, after repeated action potentials, with a distribution predominantly in neurons of the central nervous system. This isoform is encoded by the ATP1A3 gene. Pathogenic variants in this gene have been implicated in several phenotypes in the last decades. Carriers of pathogenic variants in this gene manifest neurological and non-neurological features in many combinations, usually with an acute onset and paroxysmal episodes triggered by fever or other factors. The first three syndromes described were: (1) rapid-onset dystonia parkinsonism; (2) alternating hemiplegia of childhood; and, (3) cerebellar ataxia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS syndrome). Since their original description, an expanding number of cases presenting with atypical and overlapping features have been reported. Because of this, ATP1A3-disorders are now beginning to be viewed as a phenotypic continuum representing discrete expressions along a broadly heterogeneous clinical spectrum.