Episodic Ataxia Type 1: Natural History and Effect on Quality of Life.

Episodic ataxia type 1 (EA1) is a rare autosomal potassium channelopathy, due to mutations in KCNA1. Patients have childhood onset of intermittent attacks of ataxia, dizziness or imbalance. In order to quantify the natural history of EA1, its effect on quality of life and in preparation for future clinical trials, we set up an international multi-centre study of EA1. We recruited thirty-three participants with EA1: twenty-three completed 1-year follow-up and eighteen completed 2-year follow-up. There was very little accumulation of disability or impairment over the course of the 2 years of the study. The outcome measures of ataxia (SARA and functional rating of ataxia) and the activities of daily living scale were largely stable over time. Self-reported health-related quality of life (SF-36) scores were lower across all domains than controls, in keeping with a chronic condition. Physical subdomain scores appeared to deteriorate over time, which seems to be driven by the female participants in the study. This is an interesting finding and warrants further study. Attacks of EA1 reported by participants in real time via an interactive voice response system showed that symptoms were not stereotyped; however, attack duration and frequency was stable between individuals. This large prospective study is the first ever completed in subjects with EA1. We document the natural history of the disorder over 2 years. These data will enable the development of outcome measures for clinical trials of treatment.

Mutations of EXOSC3/Rrp40p associated with neurological diseases impact ribosomal RNA processing functions of the exosome in S. cerevisiae.

The RNA exosome is a conserved multiprotein complex that achieves a large number of processive and degradative functions in eukaryotic cells. Recently, mutations have been mapped to the gene encoding one of the subunits of the exosome, EXOSC3 (yeast Rrp40p), which results in pontocerebellar hypoplasia with motor neuron degeneration in human patients. However, the molecular impact of these mutations in the pathology of these diseases is not well understood. To investigate the molecular consequences of mutations in EXOSC3 that lead to neurological diseases, we analyzed the effect of three of the mutations that affect conserved residues of EXOSC3/Rrp40p (G31A, G191C, and W238R; G8A, G148C, and W195R, respectively, in human and yeast) in S. cerevisiae We show that the severity of the phenotypes of these mutations in yeast correlate with that of the disease in human patients, with the W195R mutant showing the strongest growth and RNA processing phenotypes. Furthermore, we show that these mutations affect more severely pre-ribosomal RNA processing functions of the exosome rather than other nuclear processing or surveillance functions. These results suggest that delayed or defective pre-rRNA processing might be the primary defect responsible for the pathologies detected in patients with mutations affecting EXOSC3 function in residues conserved throughout eukaryotes.

Late-onset episodic ataxia associated with SLC1A3 mutation.

Episodic ataxia type 6 (EA6) is caused by mutations in SLC1A3 that encodes excitatory amino acid transporter 1 (EAAT1), a glial glutamate transporter. EAAT1 regulates the extent and durations of glutamate-mediated signal by the clearance of glutamate after synaptic release. In addition, EAAT1 also has an anion channel activity that prevents additional glutamate release. We identified a missense mutation in SLC1A3 in a family with EA. The proband exhibited typical EA2-like symptoms such as recurrent ataxia, slurred speech with a duration of several hours, interictal nystagmus and response to acetazolamide, but had late-onset age of sixth decade. Whole-exome sequencing detected a heterozygous c.1177G>A mutation in SLC1A3. This mutation predicted a substitution of isoleucine for a highly conserved valine residue in the seventh transmembrane domain of EAAT1. The mutation was not present in 100 controls, a large panel of in-house genome data and various mutation databases. Most functional prediction scores revealed to be deleterious. Same heterozygous mutation was identified in one clinically affected family member and two asymptomatic members. Our data expand the mutation spectrum of SLC1A3 and the clinical phenotype of EA6.

Loss of function of SLC25A46 causes lethal congenital pontocerebellar hypoplasia.

Disturbed mitochondrial fusion and fission have been linked to various neurodegenerative disorders. In siblings from two unrelated families who died soon after birth with a profound neurodevelopmental disorder characterized by pontocerebellar hypoplasia and apnoea, we discovered a missense mutation and an exonic deletion in the SLC25A46 gene encoding a mitochondrial protein recently implicated in optic atrophy spectrum disorder. We performed functional studies that confirmed the mitochondrial localization and pro-fission properties of SLC25A46. Knockdown of slc24a46 expression in zebrafish embryos caused brain malformation, spinal motor neuron loss, and poor motility. At the cellular level, we observed abnormally elongated mitochondria, which was rescued by co-injection of the wild-type but not the mutant slc25a46 mRNA. Conversely, overexpression of the wild-type protein led to mitochondrial fragmentation and disruption of the mitochondrial network. In contrast to mutations causing non-lethal optic atrophy, missense mutations causing lethal congenital pontocerebellar hypoplasia markedly destabilize the protein. Indeed, the clinical severity appears inversely correlated with the relative stability of the mutant protein. This genotype-phenotype correlation underscores the importance of SLC25A46 and fine tuning of mitochondrial fission and fusion in pontocerebellar hypoplasia and central neurodevelopment in addition to optic and peripheral neuropathy across the life span.

Two cases of rheumatoid meningitis.

Central nervous system (CNS) involvement by rheumatoid arthritis (RA) in the form of rheumatoid meningitis (RM) is rare and most commonly occurs in the setting of longstanding severe RA. Due to a wide range of clinical presentations and nonspecific laboratory findings, it presents a diagnostic challenge often requiring brain biopsy. Only a few histopathologically confirmed cases have been described in the literature. Our aim is to describe two cases of RM and review the literature. The first case is of a previously healthy 37-year-old man who presented with severe headaches and focal neurologic deficits. Magnetic resonance imaging demonstrated abnormal leptomeningeal enhancement in the left frontal and parietal sulci. The second case is of a 62-year-old woman with a history of mild chronic joint pain who presented with confusion, personality changes and seizures. Both patients ultimately underwent brain biopsy which demonstrated RM on pathologic examination. Administration of corticosteroids resulted in significant clinical improvement in both cases. To our knowledge, our unusual case of RM in the young man is the fifth reported case of rheumatoid meningitis in a patient with no prior history of RA. Such an atypical presentation makes diagnosis even more difficult and highlights the need for awareness of this entity in the diagnostic consideration of a patient presenting with unexplained neurologic symptoms. Our literature review underscores the clinical and pathologic heterogeneity of CNS involvement in RA.

C-terminal truncations in human 3'-5' DNA exonuclease TREX1 cause autosomal dominant retinal vasculopathy with cerebral leukodystrophy.

Autosomal dominant retinal vasculopathy with cerebral leukodystrophy is a microvascular endotheliopathy with middle-age onset. In nine families, we identified heterozygous C-terminal frameshift mutations in TREX1, which encodes a 3'-5' exonuclease. These truncated proteins retain exonuclease activity but lose normal perinuclear localization. These data have implications for the maintenance of vascular integrity in the degenerative cerebral microangiopathies leading to stroke and dementias.

Episodic ataxia type 1: clinical characterization, quality of life and genotype-phenotype correlation.

Episodic ataxia type 1 is considered a rare neuronal ion channel disorder characterized by brief attacks of unsteadiness and dizziness with persistent myokymia. To characterize the natural history, develop outcome measures for future clinical trials, and correlate genotype with phenotype, we undertook an international, prospective, cross-sectional study. Thirty-nine individuals (51% male) were enrolled: median age 37 years (range 15-65 years). We identified 10 different pathogenic point mutations in KCNA1 that accounted for the genetic basis of 85% of the cohort. Participants with KCNA1 mutations were more likely to have a positive family history. Analysis of the total cohort showed that the first episode of ataxia occurred before age 20 in all but one patient, with an average age of onset of 7.9 years. Physical exertion, emotional stress and environmental temperature were the most common triggers for attacks. Attack frequency ranged from daily to monthly, even with the same KCNA1 genotype. Average attack duration was in the order of minutes. Ten participants (26%) developed permanent cerebellar signs, which were related to disease duration. The average Scale for the Assessment and Rating of Ataxia score (SARA, a standardized measure of cerebellar dysfunction on clinical examination, scores range from 0-40) was an average of 3.15 for all participants (range 0-14), but was only 2 in those with isolated episodic ataxia compared with 7.7 in those with progressive cerebellar ataxia in addition to episodic ataxia. Thirty-seven participants completed the SF-36, a quality of life survey; all eight domain norm-based average scores (mean=50) were below normal with mental health being the lowest (41.3) in those with mutation positive episodic ataxia type 1. Scores on SF-36 correlated negatively with attack frequency. Of the 39 participants in the study, 33 harboured mutations in KCNA1 whereas the remaining six had no mutation identified. Episodic ataxia type 1 phenocopies have not been described previously and we report their clinical features, which appear to be different to those with a KCNA1 mutation. This large prospective study of both genetically confirmed episodic ataxia type 1 and episodic ataxia type 1 phenocopies provides detailed baseline characteristics of these disorders and their impact on participants. We found that attacks had a significant effect on quality of life. Unlike previous studies, we found that a significant number of individuals with genetically confirmed episodic ataxia type 1 (21%) had accumulated persistent cerebellar symptoms and signs. These data will enable the development of outcome measures for clinical trials of treatment.

The episodic ataxias.

The primary episodic ataxias (EAs) are a group of autosomal-dominant disorders characterized by transient recurrent incoordination and truncal instability, often triggered by physical exertion or emotional stress and variably associated with progressive baseline ataxia. There are now nine designated subtypes EA1-9 (OMIM) and late onset cerebellar ataxia with episodic features as newly designated SCA27B, based largely on genetic loci. Mutations have been identified in multiple individuals and families in 4 of the 9 EA subtypes, mostly with the onset before adulthood. This chapter focuses on the clinical assessment and management of EA, genetic diagnosis, and neurophysiologic consequences of the causative mutations in the best characterized EA syndromes: EA1 caused by mutations in KCNA1 encoding a neuronal voltage-gated potassium channel, EA2 caused by mutations in CACNA1A encoding a neuronal voltage-gated calcium channel, EA6 caused by mutations in SLC1A3 encoding a glutamate transporter that is also an anion channel, and SCA27B with late onset episodic ataxia caused by an intronic trinucleotide repeat in FGF14 encoding fibroblast growth factor 14 important in regulating the distribution of voltage-gated sodium channels in the cerebellar Purkinje and granule cells. The study of EA has illuminated previously unrecognized but important roles of ion channels and transporters in brain function with shared mechanisms underlying cerebellar ataxia, migraine, and epilepsy.

Mutations in SLC20A2 are a major cause of familial idiopathic basal ganglia calcification.

Familial idiopathic basal ganglia calcification (IBGC) or Fahr's disease is a rare neurodegenerative disorder characterized by calcium deposits in the basal ganglia and other brain regions, which is associated with neuropsychiatric and motor symptoms. Familial IBGC is genetically heterogeneous and typically transmitted in an autosomal dominant fashion. We performed a mutational analysis of SLC20A2, the first gene found to cause IBGC, to assess its genetic contribution to familial IBGC. We recruited 218 subjects from 29 IBGC-affected families of varied ancestry and collected medical history, neurological exam, and head CT scans to characterize each patient's disease status. We screened our patient cohort for mutations in SLC20A2. Twelve novel (nonsense, deletions, missense, and splice site) potentially pathogenic variants, one synonymous variant, and one previously reported mutation were identified in 13 families. Variants predicted to be deleterious cosegregated with disease in five families. Three families showed nonsegregation with clinical disease of such variants, but retrospective review of clinical and neuroimaging data strongly suggested previous misclassification. Overall, mutations in SLC20A2 account for as many as 41% of our familial IBGC cases. Our screen in a large series expands the catalog of SLC20A2 mutations identified to date and demonstrates that mutations in SLC20A2 are a major cause of familial IBGC. Non-perfect segregation patterns of predicted deleterious variants highlight the challenges of phenotypic assessment in this condition with highly variable clinical presentation.

Surveying physical therapists' understanding of benign paroxysmal positional vertigo.

Introduction: Benign paroxysmal positional vertigo (BPPV) is a common condition with disabling symptoms that is diagnosed and effectively treated at the bedside. Our encounter with patients experiencing prolonged BPPV who may not have received appropriate physical therapy prompted us to explore barriers to the diagnosis and treatment for BPPV among physical therapists, which has not been extensively investigated. We hypothesize that a potential barrier may be a lack of understanding of subtle symptoms of BPPV that deviate from the classical presentation. The gold standard for diagnosing definite BPPV is subjective dizziness or vertigo with nystagmus in response to positional testing. There are variants of BPPV including subjective BPPV (subjective dizziness or vertigo without nystagmus) and vestibular agnosia (nystagmus without subjective dizziness or vertigo) that do not meet the diagnostic criteria for definite BPPV but are equally responsive to the same repositioning maneuvers. The purpose of this project was to survey physical therapists for their understanding of BPPV including subjective BPPV and vestibular agnosia. Methods: A panel of experts created a 16-question survey, designed for physical therapists, with three categories: (1), inquiring if they treat persons with BPPV, (2) three clinical vignettes for definite BPPV, subjective BPPV, and BPPV with vestibular agnosia, and (3) demographic information. Data collection occurred at two large physical therapy meetings, one of which was a national professional meeting and the other was a professional continuing medical education course geared towards advancing vestibular rehabilitation skills. Results: There were 426 people who completed the survey, 364 of whom treat BPPV in their practice. In the first clinical vignette created to assess the respondents' understanding of definite BPPV, 229 (62%) of respondents would always assess a patient for BPPV based on complaints of a "room spinning" vertigo from head movement. When asked if the complaint was lingering "lightheadedness or feelings of imbalance" from head movement, only 158 (43%) reported they would perform positional testing to reassess. In the BPPV variant vignettes, 187 (51%) identified the patient with subjective BPPV as having BPPV and 305 (85%) identified the patient with vestibular agnosia as having BPPV. Discussion: The results of this survey demonstrate gaps in knowledge regarding BPPV across practice settings and experience, with opportunities to bridge these gaps to improve treatment for BPPV.

A C-terminal mutation of ATP1A3 underscores the crucial role of sodium affinity in the pathophysiology of rapid-onset dystonia-parkinsonism.

The Na(+)/K(+)-ATPases are ion pumps of fundamental importance in maintaining the electrochemical gradient essential for neuronal survival and function. Mutations in ATP1A3 encoding the alpha3 isoform cause rapid-onset dystonia-parkinsonism (RDP). We report a de novo ATP1A3 mutation in a patient with typical RDP, consisting of an in-frame insertion of a tyrosine residue at the very C terminus of the Na(+)/K(+)-ATPase alpha3-subunit-the first reported RDP mutation in the C terminus of the protein. Expression studies revealed that there is no defect in the biogenesis or plasma membrane targeting, although cells expressing the mutant protein showed decreased survival in response to ouabain challenge. Functional analysis demonstrated a drastic reduction in Na(+) affinity in the mutant, which can be understood by structural modelling of the E1 and E2 conformations of the wild-type and mutant enzymes on the basis of the strategic location of the C terminus in relation to the third Na(+) binding site. The dramatic clinical presentation, together with the biochemical findings, provides both in vivo and in vitro evidence for a crucial role of the C terminus of the alpha-subunit in the function of the Na(+)/K(+)-ATPase and a key impact of Na(+) affinity in the pathophysiology of RDP.

Novel de novo TREX1 mutation in a patient with retinal vasculopathy with cerebral leukoencephalopathy and systemic manifestations mimicking demyelinating disease.

Retinal vasculopathy with cerebral leukoencephalopathy and systemic manifestations (RVCL-S) is a rare fatal autosomal dominant vasculopathy associated with mutations in the TREX1 gene. Only one de novo case has been reported in the literature. We report the long-term clinical, radiological, and pathological presentation of a patient with a de novo and novel mutation in this gene. Description of the clinical, genetic, imaging and pathologic characteristics is important to better characterize RVCL-S and prevent unnecessary interventions. RVCL-S should be considered in patients with tumefactive brain lesions unresponsive to immunotherapy.

Lesion evolution and neurodegeneration in RVCL-S: A monogenic microvasculopathy.

OBJECTIVE: To characterize lesion evolution and neurodegeneration in retinal vasculopathy with cerebral leukoencephalopathy and systemic manifestations (RVCL-S) using multimodal MRI. METHODS: We prospectively performed MRI and cognitive testing in RVCL-S and healthy control cohorts. Gray and white matter volume and disruption of white matter microstructure were quantified. Asymmetric spin echo acquisition permitted voxel-wise oxygen extraction fraction (OEF) calculation as an in vivo marker of microvascular ischemia. The RVCL-S cohort was included in a longitudinal analysis of lesion subtypes in which hyperintense lesions on fluid-attenuated inversion recovery (FLAIR), T1-postgadolinium, and diffusion-weighted imaging were delineated and quantified volumetrically. RESULTS: Twenty individuals with RVCL-S and 26 controls were enrolled. White matter volume and microstructure declined faster in those with RVCL-S compared to controls. White matter atrophy in RVCL-S was highly linear (ρ = -0.908, p < 0.0001). Normalized OEF was elevated in RVCL-S and increased with disease duration. Multiple cognitive domains, specifically those measuring working memory and processing speed, were impaired in RVCL-S. Lesion volumes, regardless of subtype, progressed/regressed with high variability as a function of age, while FLAIR lesion burden increased near time to death (p < 0.001). CONCLUSION: RVCL-S is a monogenic microvasculopathy affecting predominantly the white matter with regard to atrophy and cognitive impairment. White matter volumes in RVCL-S declined linearly, providing a potential metric against which to test the efficacy of future therapies. Progressive elevation of white matter OEF suggests that microvascular ischemia may underlie neurodegeneration in RVCL-S.

Bilateral vestibulopathy: clinical, diagnostic, and genetic considerations.

Bilateral vestibulopathy is a rare, but important cause of imbalance that is underrecognized and not well understood. Clinically heterogeneous, it is variably associated with recurrent vertigo, hearing loss, migraine, peripheral neuropathy, or cerebellar degeneration. In about half of all patients with bilateral vestibulopathy, no cause can be identified. There have been several reports of familial bilateral vestibulopathy, suggesting genetic predisposition. The identification of genetic defects underlying hereditary deafness syndromes has greatly advanced the understanding of the functional components and the development of cochlea. In contrast, the progress in bilateral vestibulopathy has been slow, likely hampered by the difficulty in diagnosis outside of academic centers and a lack of animal models that recapitulate the progressive clinical features that are not apparent from birth. It is reasonable to anticipate that there will be an equally large number of genetic disorders underlying bilateral vestibulopathy as in deafness. Understanding the pathophysiology of bilateral vestibulopathy may suggest possible causes for the gradual decline in vestibular function that occurs with normal aging. Furthermore, the study of bilateral vestibulopathy may shed light on the pathophysiology of more common vestibular syndromes such as benign recurrent vertigo and vestibular migraine.

Functional neuroanatomy of the human premotor oculomotor brainstem nuclei: insights from postmortem and advanced in vivo imaging studies.

Considerable progress has been made recently in the field of the functional neuroanatomy of the primate oculomotor system, which has also improved our understanding of the structure, organization and function of the human oculomotor system. In the present review we provide for the first time an overview of the neuroanatomical basis of eye movement control in humans as revealed by a series of post-mortem studies in which the human premotor oculomotor brainstem nuclei were identified using unconventional 100 µm thick serial tissue sections stained for Nissl substance and lipofuscin pigment (Nissl-pigment stain according to Braak). Data from control brains and from patients suffering from spinocerebellar ataxia type 3, a neurodegenerative disease that severely impairs oculomotor function are discussed and recommendations for the identification of human premotor oculomotor brainstem nuclei in post-mortem studies are given. To visualize premotor brainstem nuclei in living patients, modern brain imaging techniques have been employed, albeit with limited success. Establishing topographic markers of brainstem nuclei may be a necessary next step to further elucidate the functional neuroanatomy of the premotor oculomotor brainstem network in human patients. This will help radiologists to identify these nuclei in living patients and will enable clinicians to monitor the progression of neurological disorders affecting the oculomotor system.

Phenotypic and genetic analysis of a large family with migraine-associated vertigo.

OBJECTIVES: To describe a large multigenerational family with migraine-associated vertigo (MAV) combining a detailed phenotypic and genetic analysis. BACKGROUND: Migraine-associated vertigo is said to be highly prevalent in the general population and, like other migraine syndromes, its etiology is felt to have a strong genetic component. However, so far, there have been no reports of large families with MAV. METHODS: Detailed clinical study was conducted on a large multigenerational family with MAV. Genetic study using identical-by-descent analysis with dense single nucleotide polymorphism (SNP) arrays was performed to examine consistent inheritance pattern among the affecteds. RESULTS: Clinical features of MAV were variable although most had other migraine symptoms with at least some of their attacks. We did not find a region of the genome shared by all eight subjects with MAV indicating a polygenetic inheritance for MAV even in this single large family. CONCLUSIONS: A region on 11q shared by most affected females may contain a susceptibility allele for MAV that is expressed exclusively or predominantly by women.

Progressive cerebellar ataxia with variable episodic symptoms--phenotypic diversity of R1668W CACNA1A mutation.

We describe a family with an R1668W mutation in the CACNA1A gene who presented with a broader clinical spectrum and more variable features than previously reported. The mother had a pure progressive cerebellar ataxia of late onset with downbeat nystagmus, whereas her daughter suffered from episodic ataxia, hemiplegic migraine, and progressive cerebellar ataxia with horizontal gaze-evoked and rebound nystagmus. In both patients, treatment with acetazolamide was ineffective and worsened baseline ataxia, whereas flunarizine ameliorated episodic symptoms. Our report highlights profound phenotypic variability that can be associated with CACNA1A mutations and adds important therapeutic considerations.