Phenotypic features of Huntington's disease-like 2

Recent advances in non-Huntington's disease choreas

INTRODUCTION

Chorea is primarily due to an imbalance of basal ganglia output pathways, often due to dysfunction or degeneration of the caudate nucleus and putamen, and can be due to many causes.

METHODS

We reviewed the recent literature to identify newly-recognized causes of chorea, including auto-immune, metabolic, and genetic. We also focused upon developments in mechanisms relating to underlying pathophysiology of certain genetic choreas and advances in therapeutics.

RESULTS

Novel autoantibodies continue to be identified as causes of chorea. Both COVID-19 infection and vaccination are reported to result rarely in chorea, although in some cases causality is not clearly established. Advances in genetic testing continue to find more causes of chorea, and to expand the phenotype of known genetic disorders. Deep brain stimulation can be successful in certain circumstances.

CONCLUSION

Our understanding of mechanisms underlying this movement disorder continues to advance, however much remains to be elucidated.

Huntington disease-like 2: insight into neurodegeneration from an African disease

Huntington disease (HD)-like 2 (HDL2) is a rare genetic disease caused by an expanded trinucleotide repeat in the JPH3 gene (encoding junctophilin 3) that shows remarkable clinical similarity to HD. To date, HDL2 has been reported only in patients with definite or probable African ancestry. A single haplotype background is shared by patients with HDL2 from different populations, supporting a common African origin for the expansion mutation. Nevertheless, outside South Africa, reports of patients with HDL2 in Africa are scarce, probably owing to limited clinical services across the continent. Systematic comparisons of HDL2 and HD have revealed closely overlapping motor, cognitive and psychiatric features and similar patterns of cerebral and striatal atrophy. The pathogenesis of HDL2 remains unclear but it is proposed to occur through several mechanisms, including loss of protein function and RNA and/or protein toxicity. This Review summarizes our current knowledge of this African-specific HD phenocopy and highlights key areas of overlap between HDL2 and HD. Given the aforementioned similarities in clinical phenotype and pathology, an improved understanding of HDL2 could provide novel insights into HD and other neurodegenerative and/or trinucleotide repeat expansion disorders.

Movement Disorders and Hematologic Diseases

BACKGROUND

Movement disorders can be associated with or caused by hematological abnormalities. The objective of this review is to highlight features that will aid in the clinician's recognition and treatment of these disorders.

METHODS

MESH terms relevant to movement disorders and hematologic diseases were searched to identify conditions included in this narrative, educational review.

RESULTS

Several conditions were identified, and they were organized by hematologic categories to include red blood cell abnormalities, white blood cell abnormalities, disorders of clotting and bleeding, hematologic malignancies, and others.

CONCLUSIONS

This review will increase providers' understanding of disorders that include movement disorders and hematologic abnormalities. Basic hematologic laboratories can aid in assessment of these disorders, to include complete blood count/hemogram and peripheral blood smear. Recognition is key, especially in the setting of underlying malignancy, vitamin deficiency, or other disorder in which treatment is available.

The Neuropsychiatry of Huntington Disease-Like 2: A Comparison with Huntington's Disease

BACKGROUND

Huntington Disease-Like 2 (HDL2) is a rare autosomal dominant disorder caused by an abnormal CAG/CTG triplet repeat expansion on chromosome 16q24. The symptoms of progressive decline in motor, cognitive and psychiatric functioning are similar to those of Huntington's disease (HD). The psychiatric features of the HDL2 have been poorly characterized.

OBJECTIVE

To describe the neuropsychiatric features of HDL2 and compare them with those of HD.

METHODS

A blinded cross-sectional design was used to compare the behavioural component of the Unified Huntington's Disease Rating Scale (UHDRS) in participants with HDL2 (n = 15) and HD (n = 13) with African ancestry.

RESULTS

HDL2 patients presented with psychiatric symptoms involving mood disturbances and behavioural changes that were not significantly different from those in the HD group. Duration of disease and motor performance correlated (p < 0.001) with the Functional Capacity score and the Independence score of the UHDRS. HD patients reported movement dysfunction as the first symptom more frequently than HDL2 Patients (p < 0.001).

CONCLUSION

The psychiatric phenotype of HDL2 is similar to that of HD and linked to motor decline and disease duration. Psychiatric symptoms seem more severe for HDL2 patients in the early stages of the disease.

Review of Hereditary and Acquired Rare Choreas

Background:

Movement disorders are often a prominent part of the phenotype of many neurologic rare diseases. In order to promote awareness and diagnosis of these rare diseases, the International Parkinson’s and Movement Disorders Society Rare Movement Disorders Study Group provides updates on rare movement disorders.

Methods:

In this narrative review, we discuss the differential diagnosis of the rare disorders that can cause chorea.

Results:

Although the most common causes of chorea are hereditary, it is critical to identify acquired or symptomatic choreas since these are potentially treatable conditions. Disorders of metabolism and mitochondrial cytopathies can also be associated with chorea.

Discussion:

The present review discusses clues to the diagnosis of chorea of various etiologies. Authors propose algorithms to help the clinician in the diagnosis of these rare disorders.

A comparison between the neurocognitive profile of Huntington Disease-Like 2 and Huntington Disease: Exploring the presence of double dissociations

Huntington Disease Like-2 (HDL2) is a rare autosomal dominant genetic disease caused by a mutation in the JPH3 gene. HDL2 is the Huntington Disease (HD) phenocopy that has the greatest clinical resemblance to HD. Both are characterized by movement, psychiatric and cognitive dysfunction, which progress to dementia. The present study compared the neuropsychological profile of HDL2 with that of HD. Using a Single Case-Control Methodology in Neuropsychology, three HDL2 and seven matched HD patients were assessed with a comprehensive neuropsychological battery and compared to matched control samples, considering age, years of education, type of school (public/government) and language (all bi/multilingual). Potential double dissociations were explored by using Crawford, Garthwaite, and Wood's Inferential Methods for Comparing the Scores of Two Single-Cases in Case-Control Designs. Double dissociation between HDL2 and HD were identified in three tests, namely Letter Number Sequencing, Rey Auditory Learning Test Delayed and Recognition Trials. These dissociations possible are due to methodological limitations.

Huntington's disease in the United States: Variation by demographic and socioeconomic factors

BACKGROUND

Despite extensive research regarding the etiology of Huntington's disease, relatively little is known about the epidemiology of this rare disorder, particularly in the United States where there are no national-scale estimates of the disease.

OBJECTIVES

To provide national-scale estimates of Huntington's disease in a U.S. population and to test whether disease rates are increasing, and whether frequency varies by race, ethnicity, or other factors.

METHODS

Using an insurance database of over 67 million enrollees, we retrospectively identified a cohort of 3,707 individuals diagnosed with Huntington's disease between 2003 and 2016. We estimated annual incidence, annual diagnostic frequency, and tested for trends over time and differences in diagnostic frequency by sociodemographic characteristics.

RESULTS

During the observation period, the age-adjusted cumulative incidence rate was1.22 per 100,000 persons (95% confidence interval: 1.53, 1.65), and age-adjusted diagnostic frequency was 6.52 per 100,000 persons (95% confidence interval: 5.31, 5.66); both rates remained relatively stable over the 14-year period. We identified several previously unreported differences in Huntington's disease frequency by self-reported sex, income, and race/ethnicity. However, racial/ethnic differences were of lower magnitude than have previously been reported in other country-level studies.

CONCLUSIONS

In these large-scale estimates of U.S. Huntington's disease epidemiology, we found stable disease frequency rates that varied by several sociodemographic factors. These findings suggest that disease patterns may be more driven by social or environmental factors than has previously been appreciated. Results further demonstrate the potential utility of administrative Big Data in rare disease epidemiology when other data sources are unavailable. © 2019 International Parkinson and Movement Disorder Society.

Comparison of the Huntington's Disease like 2 and Huntington's Disease Clinical Phenotypes

Background

Huntington's disease like 2 (HDL2) is the most common Huntington's disease (HD) phenocopy in many countries and described as the phenocopy with the greatest resemblance to HD. The current clinical description of HDL2 is based on retrospective data. It is unknown whether HDL2 has clinical features that distinguish it from HD.

Objective

To describe the HDL2 phenotype and compare it to HD systematically.

Methods

A blinded cross-sectional design was used to compare the HDL2 (n = 15) and HD (n = 13) phenotypes. African ancestry participants underwent assessments, including the Unified Huntington's Disease Rating Scale (UHDRS). The UHDRS motor component was video recorded and evaluated by blinded experts and the inter-rater reliability calculated.

Results

Both groups were homogeneous in terms of demographics and disease characteristics. However, HDL2 patients presented three years earlier with more prominent dysarthria and dystonia. Raters could not distinguish between the two diseases with a high level of agreement. No significant differences in the TMS between HDL2 and HD were found. In both disorders, disease duration correlated with motor scores, with the exception of chorea. Psychiatric and cognitive scores were not significantly different between the groups.

Conclusions

The HDL2 phenotype is similar to HD and is initially characterized by dementia, chorea, and oculomotor abnormalities, progressing to a rigid and bradykinetic state, suggesting the UHDRS is useful to monitor disease progression in HDL2. Although HDL2 patients scored higher on some UHDRS domains, this did not differentiate between the two diseases; it may however be emerging evidence of HDL2 having a more severe clinical phenotype.

Emerging differences between Huntington's disease-like 2 and Huntington's disease: A comparison using MRI brain volumetry

Huntington's Disease-Like 2 (HDL2), caused by a CTG/CAG expansion in JPH3 on chromosome 16q24, is the most common Huntington's Disease (HD) phenocopy in populations with African ancestry. Qualitatively, brain MRIs of HDL2 patients have been indistinguishable from HD. To determine brain regions most affected in HDL2 a cross-sectional study using MRI brain volumetry was undertaken to compare the brains of nine HDL2, 11 HD and nine age matched control participants. Participants were ascertained from the region in South Africa with the world's highest HDL2 incidence. The HDL2 and HD patient groups showed no significant differences with respect to mean age at MRI, disease duration, abnormal triplet repeat length, or age at disease onset. Overall, intracerebral volumes were smaller in both affected groups compared to the control group. Comparing the HDL2 and HD groups across multiple covariates, cortical and subcortical volumes were similar with the exception that the HDL2 thalamic volumes were smaller. Consistent with other similarities between the two diseases, these results indicate a pattern of neurodegeneration in HDL2 that is remarkably similar to HD. However smaller thalamic volumes in HDL2 raises intriguing questions into the pathogenesis of both disorders, and how these volumetric differences relate to their respective phenotypes.

A Systematic Review of the Huntington Disease-Like 2 Phenotype

BACKGROUND

Huntington Disease-like 2 (HDL2) is a neurodegenerative disorder similar to Huntington Disease (HD) in its clinical phenotype, genetic characteristics, neuropathology and longitudinal progression. Proposed specific differences include an exclusive African ancestry, lack of eye movement abnormalities, increased Parkinsonism, and acanthocytes in HDL2.

OBJECTIVE

The objective was to determine the similarities and differences between HD and HDL2 by establishing the clinical phenotype of HDL2 with the published cases.

METHODS

A literature review of all clinically described cases of HDL2 until the end of 2016 was performed and a descriptive analysis was carried out.

RESULTS

Sixty-nine new cases were described between 2001 and 2016. All cases had likely African ancestry, and most were found in South Africa and the USA. Many features were found to be similar to HD, including a strong negative correlation between repeat length and age of onset. Chorea was noted in 48/57 cases (84%). Dementia was reported in 74% patients, and Parkinsonism in 37%. Psychiatric features were reported in 44 out of 47 cases. Patients with chorea had lower expanded repeat lengths compared to patients without chorea. Eye movements were described in 19 cases, 8 were abnormal. Acanthocytes were detected in 4 of the 13 patients tested. Nineteen out of 20 MRIs were reported as abnormal with findings similar to HD.

CONCLUSION

This review clarifies some aspects of the HDL2 phenotype and highlights others which require further investigation. Features that are unique to HDL2 have been documented in a minority of subjects and require prospective validation.

Quantitative Proteomic Analysis Reveals Similarities between Huntington's Disease (HD) and Huntington's Disease-Like 2 (HDL2) Human Brains

The pathogenesis of HD and HDL2, similar progressive neurodegenerative disorders caused by expansion mutations, remains incompletely understood. No systematic quantitative proteomics studies, assessing global changes in HD or HDL2 human brain, were reported. To address this deficit, we used a stable isotope labeling-based approach to quantify the changes in protein abundances in the cortex of 12 HD and 12 control cases and, separately, of 6 HDL2 and 6 control cases. The quality of the tissues was assessed to minimize variability due to post mortem autolysis. We applied a robust median sweep algorithm to quantify protein abundance and performed statistical inference using moderated test statistics. 1211 proteins showed statistically significant fold changes between HD and control tissues; the differences in selected proteins were verified by Western blotting. Differentially abundant proteins were enriched in cellular pathways previously implicated in HD, including Rho-mediated, actin cytoskeleton and integrin signaling, mitochondrial dysfunction, endocytosis, axonal guidance, DNA/RNA processing, and protein transport. The abundance of 717 proteins significantly differed between control and HDL2 brain. Comparative analysis of the disease-associated changes in the HD and HDL2 proteomes revealed that similar pathways were altered, suggesting the commonality of pathogenesis between the two disorders.

Junctophilin 3 (JPH3) expansion mutations causing Huntington disease like 2 (HDL2) are common in South African patients with African ancestry and a Huntington disease phenotype

Huntington disease (HD) is a progressive autosomal dominant neurodegenerative disorder, characterized by abnormal movements, cognitive decline, and psychiatric symptoms, caused by a CAG repeat expansion in the huntingtin (HTT) gene on chromosome 4p. A CAG/CTG repeat expansion in the junctophilin-3 (JPH3) gene on chromosome 16q24.2 causes a Huntington disease-like phenotype (HDL2). All patients to date with HDL2 have some African ancestry. The present study aimed to characterize the genetic basis of the Huntington disease phenotype in South Africans and to investigate the possible origin of the JPH3 mutation. In a sample of unrelated South African individuals referred for diagnostic HD testing, 62% (106/171) of white patients compared to only 36% (47/130) of black patients had an expansion in HTT. However, 15% (20/130) of black South African patients and no white patients (0/171) had an expansion in JPH3, confirming the diagnosis of Huntington disease like 2 (HDL2). Individuals with HDL2 share many clinical features with individuals with HD and are clinically indistinguishable in many cases, although the average age of onset and diagnosis in HDL2 is 5 years later than HD and individual clinical features may be more prominent. HDL2 mutations contribute significantly to the HD phenotype in South Africans with African ancestry. JPH3 haplotype studies in 31 families, mainly from South Africa and North America, provide evidence for a founder mutation and support a common African origin for all HDL2 patients. Molecular testing in individuals with an HD phenotype and African ancestry should include testing routinely for JPH3 mutations.

Untangling the Thorns: Advances in the Neuroacanthocytosis Syndromes

There have been significant advances in neuroacanthocytosis (NA) syndromes in the past 20 years, however, confusion still exists regarding the precise nature of these disorders and the correct nomenclature. This article seeks to clarify these issues and to summarise the recent literature in the field. The four key NA syndromes are described here-chorea-acanthocytosis, McLeod syndrome, Huntington's disease-like 2, and pantothenate kinase- associated neurodegeneration. In the first two, acanthocytosis is a frequent, although not invariable, finding; in the second two, it occurs in approximately 10% of patients. Degeneration affecting the basal ganglia is the key neuropathologic finding, thus the clinical presentations can be remarkably similar. The characteristic phenotype comprises a variety of movement disorders, including chorea, dystonia, and parkinsonism, and also psychiatric and cognitive symptoms attributable to basal ganglia dysfunction. The age of onset, inheritance patterns, and ethnic background differ in each condition, providing diagnostic clues. Other investigations, including routine blood testing and neuroimaging can be informative. Genetic diagnosis, if available, provides a definitive diagnosis, and is important for genetic counseling, and hopefully molecular therapies in the future. In this article I provide a historical perspective on each NA syndrome. The first 3 disorders, chorea-acanthocytosis, McLeod syndrome, Huntington's disease-like 2, are discussed in detail, with a comprehensive review of the literature to date for each, while pantothenate kinase-associated neurodegeneration is presented in summary, as this disorder has recently been reviewed in this journal. Therapy for all of these diseases is, at present, purely symptomatic.

Clinical and molecular research of neuroacanthocytosis

Neuroacanthocytosis is an autosomal recessive or dominant inherited disease characterized by widespread, non-specific nervous system symptoms, or spiculated "acanthocytic" red blood cells. The clinical manifestations typically involve chorea and dystonia, or a range of other movement disorders. Psychiatric and cognitive symptoms may also be present. The two core neuroacanthocytosis syndromes, in which acanthocytosis is atypical, are autosomal recessive chorea-acanthocytosis and X-linked McLeod syndrome. Acanthocytes are found in a smaller proportion of patients with Huntington's disease-like 2 and pantothenate kinase-associated neurodegeneration. Because the clinical manifestations are diverse and complicated, in this review we present features of inheritance, age of onset, neuroimaging and laboratory findings, as well as the spectrum of central and peripheral neurological abnormalities and extraneuronal involvement to help distinguish the four specific syndromes.

Loss of junctophilin-3 contributes to Huntington disease-like 2 pathogenesis

OBJECTIVE

Huntington disease-like 2 (HDL2) is a progressive, late onset autosomal dominant neurodegenerative disorder, with remarkable similarities to Huntington disease (HD). HDL2 is caused by a CTG/CAG repeat expansion. In the CTG orientation, the repeat is located within the alternatively spliced exon 2A of junctophilin-3 (JPH3), potentially encoding polyleucine and polyalanine, whereas on the strand antisense to JPH3, the repeat is in frame to encode polyglutamine. The JPH3 protein product serves to stabilize junctional membrane complexes and regulate neuronal calcium flux. We have previously demonstrated the potential pathogenic properties of JPH3 transcripts containing expanded CUG repeats. The aim of this study was to test the possibility that loss of JPH3 expression or expanded amino acid tracts also contribute to HDL2 pathogenesis.

METHODS

Transcripts from the HDL2 locus, and their protein products, were examined in HDL2, HD, and control frontal cortex. The effect of loss of Jph3 was examined in mice with partial or complete loss of Jph3.

RESULTS

Bidirectional transcription occurs at the HDL2 locus, although expression of antisense transcripts with expanded CAG repeats is limited. Protein products with expanded amino acid tracts were not detected in HDL2 brain. However, JPH3 transcripts and full-length JPH3 protein are decreased in HDL2 brain, and Jph3 hemizygous and null mice exhibit abnormal motor function.

INTERPRETATION

Our results suggest that the pathogenic mechanism of HDL2 is multifactorial, involving both a toxic gain of function of JPH3 RNA and a toxic loss of JPH3 expression.

Differential diagnosis of chorea

Chorea is a common movement disorder that can be caused by a large variety of structural, neurochemical (including pharmacologic), or metabolic disturbances to basal ganglia function, indicating the vulnerability of this brain region. The diagnosis is rarely indicated by the simple phenotypic appearance of chorea, and can be challenging, with many patients remaining undiagnosed. Clues to diagnosis may be found in the patient's family or medical history, on neurologic examination, or upon laboratory testing and neuroimaging. Increasingly, advances in genetic medicine are identifying new disorders and expanding the phenotype of recognized conditions. Although most therapies at present are supportive, correct diagnosis is essential for appropriate genetic counseling, and ultimately, for future molecular therapies.

Neuroacanthocytosis

The term "neuroacanthocytosis" describes a heterogeneous group of molecularly-defined disorders which result in progressive neurodegeneration, predominantly of the basal ganglia, and erythrocyte acanthocytosis. The clinical presentation of neuroacanthocytosis syndromes typically involves chorea and dystonia, but a range of other movement disorders may be seen. Psychiatric and cognitive symptoms may be prominent. There can be considerable phenotypic overlap; however, features of inheritance, age of onset, neuroimaging and laboratory findings, in addition to the spectrum of central and peripheral neurological abnormalities and extraneuronal involvement, can help to distinguish the specific syndromes. The two core neuroacanthocytosis syndromes, in which acanthocytosis is a typical, although not invariable finding, are autosomal recessive chorea-acanthocytosis and X-linked McLeod syndrome. Acanthocytes are found in a smaller proportion of patients with Huntington's disease-like 2 and pantothenate kinase-associated neurodegeneration. Additionally, acanthocytosis has been reported in a few patients with other neurological disorders. The causative genes do not appear to be linked by a specific function or pathway, although abnormalities of membrane processing may be implicated. The connection between the erythrocyte membrane abnormality, which results in the characteristic "thorny" protrusions, the vulnerability of the basal ganglia, and the respective genetic mutations, is obscure.

Huntington's disease-like 2 in Brazil--report of 4 patients

Huntington's disease-like 2 (HDL2) is a neurodegenerative disorder found in people of African ancestry with clinical, radiological, and neuropathological manifestations similar to Huntington's disease (HD). HDL2 is caused by a pathological expansion of CAG/CTG triplets in exon 2A of the JPH3 gene. We describe four cases of HDL2 from four unrelated families, and discuss their clinical findings. HDL2 should be considered in every patient with an HD-like phenotype who tests negative for the HD mutation, even if African ancestry is not immediately apparent.

A comparison of huntington disease and huntington disease-like 2 neuropathology

Huntington disease-like 2 (HDL2) is an autosomal dominant disorder characterized by adult-onset, progressive motor abnormalities, psychiatric disturbances, and dementia ending in premature death. Clinically, it most closely resembles Huntington disease (HD), although a subset of affected individuals have parkinsonian features. Here, we systematically compare 5 HDL2 and 5 HD brains with the hypothesis that, reflecting the clinical presentation, the neuropathology of the 2 diseases would be similar. Gross and microscopic examination revealed prominent striatal neuron loss and astrocytic gliosis in a dorsal to ventral gradient in each disorder and cortical atrophy. Nuclear protein aggregates were as common in HDL2 as in HD, and the ultrastructural features of HDL2 and HD aggregates were similar. Electron microscopy also revealed degenerating neurons, some with evidence of autophagy, in both HDL2 and HD. Small ribonuclear foci, previously associated with potentially neurotoxic RNA transcripts in HDL2, rarely colocalized with protein aggregates in HDL2 brain, although the protein aggregates were stained by anti-TATA-box binding protein antibodies. Overall, the neuropathologic features of HDL2 and HD are very similar but not identical, suggesting that the pathogenetic mechanisms of the 2 diseases may partially overlap.

Huntington disease-like 2: the first patient with apparent European ancestry

Huntington disease-like 2 (HDL2) is a rare autosomal dominant disorder of the nervous system, apparently indistinguishable from Huntington disease (HD). HDL2 is caused by the expansion above 40 CTG/CAG repeats, in a variably spliced exon of the junctophilin-3 gene, on chromosome 16q24.3. All patients described so far have been of African ancestry. A clinical evaluation, including the Unified Huntington's Disease Rating Scale, and brain Magnetic resonance imaging were achieved in a 48-year-old Brazilian man of apparent European extraction, and presenting a picture very suggestive of HD. Gene mutation analysis (HD, HDL1, HDL2, dentatorubralpallidoluysian atrophy and spinocerebellar ataxia 17) was performed. After exclusion of the HD mutation and other HDL disorders, we identified an expansion of 47 CTG/CAG at the HDL2 locus. To clarify the origin of the mutation and estimate the patient's ancestry, we performed haplotype studies and used the insertion/deletion polymorphisms method. Despite the fact that this patient had an estimated likelihood of 97.4% of being of European ancestry, the haplotype containing the expanded allele has been found only in Africans. Thus, this is the first HDL2 case reported in a patient with an apparent European ancestry, although bearing an African HDL2 haplotype. This work stresses the importance of performing the diagnosis of HDL2 in HD-like patients of various ethnicities, and particularly in highly mixed populations.

A South African mixed ancestry family with Huntington disease-like 2: Clinical and genetic features

Huntington disease-like 2 (HDL2) is a neurodegenerative disorder caused by an expansion of a CTG repeat in the junctophilin-3 gene (JPH3). A limited number of HDL2 families have been reported, all of apparently Black African ancestry. We report on a South African family that presented with progressive dementia and a movement disorder affecting numerous family members. Genotyping of the JPH3 CTG repeat revealed pathogenic expansions in three affected individuals. Whereas HDL2 is thought to be clinically indistinguishable from Huntington disease (HD), 2 of the patients in this study presented with clinical symptoms that differed substantially from HD; one had myoclonus and the other had Parkinsonism. Moreover, brain magnetic resonance imaging scans of these patients showed imaging features atypical for HD. Mitochondrial DNA and Y-chromosome DNA analysis on a family member showed that his maternal and paternal ancestries are typical of that found among the South African mixed ancestry or colored population. A difference in the distribution of CTG repeats between Caucasian and Black individuals was detected. We conclude that the phenotype of HDL2 is broad and can differ from that of typical HD. The diagnosis therefore should be considered in a wide spectrum of neuropsychiatric and abnormal movement presentations.

Huntington's disease like-2 neuropathology

Huntington's disease like-2 (HDL-2) neurodegeneration is a recently described autosomal dominant disorder with features similar to Huntington's disease (HD). Only one case report has described neuropathology from an affected patient. We describe the clinical presentation and illustrate the pathology in two additional molecularly confirmed patients, compare these with the previously published case, and contrast them with HD. We examined two patients with HDL-2. Their charts were reviewed, their brains were examined using standard neuropathology techniques, including immunoperoxidase stains, and their diagnoses were confirmed with a PCR-based assay for repeat length. The first patient presented with obsessive suspiciousness, while the second had depression and decreased visual acuity. Both patients developed increased tone and cogwheel rigidity, but neither developed choreoathetosis. Extensive degeneration affected the caudate nucleus and putamen, especially dorsally and laterally. In addition, the first patient showed lateral temporal, lateral frontal, and orbitofrontal cortical atrophy, while the second patient displayed marked degeneration in the occipital and parietal cortices. Neither patient showed significant changes in the cerebellum or brainstem. Both cases had ubiquitin-immunoreactive neuronal intranuclear inclusions (NII). The patients with of HDL-2 reviewed here were remarkable for significant frontal inhibition with parkinsonism, a lack of choreiform movements, and African ancestry. Pathologically, HDL-2 is similar to HD in its effect on the neostriatum but may differ, at least in some cases, in its degree of focal cortical involvement, including the occipital lobe.

Primary skeletal muscle involvement in chorea-acanthocytosis

Chorea-acanthocytosis (ChAc) is a hereditary disease characterized by involuntary movements and amyotrophy with elevation of serum creatine kinase. Although skeletal muscle involvement in ChAc has been suggested, the mechanism remains unclear. To investigate chorein abnormalities of the skeletal muscles of ChAc patients with an apparently heterozygous VPS13A mutation compared with those of other hereditary choreic diseases, we performed histological and immunohistochemical studies of the skeletal muscles from 3 ChAc, 1 Huntington's disease (HD), 1 McLeod syndrome (MLS), and 1 normal control (NC) with 2 originally generated anti-chorein antibodies. Chorein immunoreactivities in HD, MLS, and NC were found linearly along the sarcolemma and appeared as speckles in the sarcoplasma, but those in ChAc were uneven and discontinuous along the sarcolemmas and increased in the sarcoplasma especially in type I fibers. This histological observation suggests chorein abnormalities of skeletal muscles might be associated with primary involvement of skeletal muscles in this disorder.

Huntington's disease--like 2 is associated with CUG repeat-containing RNA foci

OBJECTIVE

Huntington's disease-like 2 (HDL2) is caused by a CAG/CTG expansion mutation on chromosome 16q24.3. The repeat falls, in the CTG orientation, within a variably spliced exon of junctophilin-3 (JPH3). The existence of a JPH3 splice variant with the CTG repeat in 3' untranslated region suggested that transcripts containing an expanded CUG repeat could play a role in the pathogenesis of HDL2, similar to the proposed pathogenic role of expanded CUG repeats in myotonic dystrophy type 1 (DM1). The goal of this study, therefore, was to test the plausibility of an RNA gain-of-function component in the pathogenesis of HDL2.

METHODS

The presence and composition of RNA foci in frontal cortex from HDL2, Huntington's disease, DM1, and control brains were investigated by in situ hybridization and immunohistochemistry. An untranslatable JPH3 transcript containing either a normal or an expanded CUG repeat was engineered and expressed in human embryonic kidney 293 and HT22 cells to further test the toxic RNA hypothesis. The formation of RNA foci and the extent of cell death were quantified.

RESULTS

RNA foci resembling DM1 foci were detected in neurons in HDL2 cortex and other brain regions. Similar to DM1, the foci colocalize with muscleblind-like protein 1, and nuclear muscleblind-like protein 1 in HDL2 cortical neurons is decreased relative to controls. In cell experiments, expression of a JPH3 transcript with an expanded CUG repeat resulted in the formation of RNA foci that colocalized with muscleblind-like protein 1 and in cell toxicity.

INTERPRETATION

These results imply that RNA toxicity may contribute to the pathogenesis of HDL2.

A case of late-onset chorea

Background A 75-year-old woman with rheumatoid arthritis presented with a 4-year history of chorea to a hospital movement disorder clinic. The involuntary movements were initially mild, affecting only the right side of the body, but gradually worsened and became bilateral. There was no relevant family history. Medications included hormone replacement therapy (HRT), diclofenac sodium, vitamin D, folic acid, methotrexate and zopiclone. On examination, bilateral choreiform movements were seen, affecting the face and limbs, with the right side more severely affected than the left. Investigations Neuropsychological testing, laboratory blood and DNA testing, echocardiogram, MRI of the brain, and brain perfusion single-photon emission computed tomography (SPECT) scanning.Diagnosis HRT-related chorea, possibly caused by a predisposition secondary to rheumatoid arthritis and small-vessel ischemic disease, or subclinical childhood rheumatic fever. Management Discontinuation of HRT.

Seminar on choreas

Chorea is one of the major types of involuntary movement disorders originating from dysfunctional neuronal networks interconnecting the basal ganglia and frontal cortical motor areas. The syndrome is characterised by a continuous flow of random, brief, involuntary muscle contractions and can result from a wide variety of causes. Diagnostic work-up can be straightforward in patients with a positive family history of Huntington's disease or acute-onset hemichorea in patients with lacunar stroke, but it can be a challenging and complex task in rare autoimmune or genetic choreas. Principles of management focus on establishing an aetiological classification and, if possible, removal of the cause. Preventive strategies may be possible in Huntington's disease where genetic counselling plays a major part. In this review we summarise the current understanding of the neuroanatomy and pathophysiology of chorea, its major aetiological classes, and principles of diagnostic work-up and management.

Young-onset dementia: a practical approach to diagnosis

BACKGROUND

Young-onset dementia is best defined as dementia presenting at age less than 65 years. And, while cognitive impairment in the elderly is dominated by dementia of the Alzheimer type, young-onset dementia has a vast differential diagnosis.

REVIEW SUMMARY

This article reviews an extensive differential diagnosis for young-onset dementia by utilizing different clues in the historical records and laboratory findings to aid with diagnosis. Laboratory testing should be completed in at least 2 stages. In the first stage, referred to as the first "wave," we suggest more routine testing, particularly for treatable causes of dementia. The second "wave," which we also outline, emphasizes more esoteric testing that may require referral to a tertiary care medical facility. The manuscript is divided into 2 parts, with part 1 focusing on clues from the historical data, while part 2 focuses on laboratory abnormalities.

CONCLUSION

Unlike dementia presenting in the elderly, the differential diagnosis in young-onset dementia is vast. A thorough historical review of the symptoms, with special emphasis on the pattern of cognitive impairment, temporal profile of the disease, detailed family history, and extensive but coordinated laboratory and ancillary testing, may yield subtle clues to the diagnosis.

Neuroacanthocytosis

PURPOSE OF REVIEW

The term neuroacanthocytosis describes a group of phenotypically and genetically heterogeneous disorders, and thus has long been a source of confusion and diagnostic imprecision. It is vital to distinguish between the lipoprotein deficiency disorders which affect gait, but do not cause movement disorders or neuropsychiatric problems, and the diseases described here, of which these are characteristic features. This review summarizes the current state of knowledge regarding this group of diseases in order to facilitate clinical recognition, accurate diagnosis and appropriate management.

RECENT FINDINGS

Advances in molecular medicine have enabled us to distinguish precisely among the disorders described under the label of neuroacanthocytosis, most notably between autosomal recessive chorea-acanthocytosis and the X-linked McLeod syndrome. This has facilitated appreciation of the range of phenotypes in each of the various conditions. Acanthocytosis is also found in a smaller percentage of cases with pantothenate kinase-associated neurodegeneration (PKAN) and Huntington's disease-like 2 (HDL2). An improved method of determination of acanthocytosis has been described, which if adopted as standard practice may facilitate detection of these conditions.

SUMMARY

Genetic testing has led to increased diagnostic accuracy of the neuroacanthocytosis syndromes, which is essential to extend recognition of these disorders, as well as to improve understanding of the disease process. Most importantly, given the absence of a cure, it is vital for appropriate genetic counselling. Treatments, as in other neurodegenerative conditions, are at present limited to symptomatic therapies.

Huntington's Disease-like 2 (HDL2) in North America and Japan

Huntington's Disease-like 2 (HDL2) is a progressive, autosomal dominant, neurodegenerative disorder with marked clinical and pathological similarities to Huntington's disease (HD). The causal mutation is a CTG/CAG expansion mutation on chromosome 16q24.3, in a variably spliced exon of junctophilin-3. The frequency of HDL2 was determined in nine independent series of patients referred for HD testing or selected for the presence of an HD-like phenotype in North America or Japan. The repeat length, ancestry, and age of onset of all North American HDL2 cases were determined. The results show that HDL2 is very rare, with a frequency of 0 to 15% among patients in the nine case series with an HD-like presentation who do not have the HD mutation. HDL2 is predominantly, and perhaps exclusively, found in individuals of African ancestry. Repeat expansions ranged from 44 to 57 triplets, with length instability in maternal transmission detected in a repeat of r2=0.29, p=0.0098). The results further support the evidence that the repeat expansion at the chromosome 16q24.3 locus is the direct cause of HDL2 and provide preliminary guidelines for the genetic testing of patients with an HD-like phenotype.

Neuroacanthocytosis: new developments in a neglected group of dementing disorders

Neurological abnormalities associated with spiculated, "acanthocytic" red cells in blood have been summarized as neuroacanthocytosis. This is a heterogeneous group of conditions that can now be clearly subdivided on the basis of genetic discoveries. The core neuroacanthocytosis syndromes are autosomal recessive chorea-acanthocytosis (ChAc) and the X-linked McLeod syndrome (MLS). Huntington's disease-like 2 (HLD2) and pantothenate kinase associated neurodegeneration (PKAN) can now also be included. All of these share dyskinesias, cognitive deterioration and progressive neurodegeneration mainly of the basal ganglia, but they are sufficiently distinct to permit a specific working diagnosis on the basis of clinical, laboratory and imaging findings. In addition, the VPS13A (formerly called CHAC), XK, JPH3 and PANK2 genes, respectively, may be examined for mutations. Unfortunately, little is yet known about the normal and abnormal physiology of the protein products of these genes, but they appear to be involved in membrane function and intracellular protein sorting. Since no cures are yet available, development and study of disease models in experimental animals (mouse, C. elegans) is a priority for current research. From a clinical point of view, the common occurrence of cardiomyopathy in MLS, the transfusion hazards due to the McLeod Kell phenotype and the possibility of improving the violent trunk spasms and orofacial dyskinesias typical for ChAc (with subsequent lip or tongue mutilations and feeding dystonia) by deep brain surgery or stimulation should be considered in patient management.

Gene-environment interplay in neurogenesis and neurodegeneration

Factors associated with predisposition and vulnerability to neurodegenerative disorders may be described usefully within the context of gene-environment interplay. There are many identified genetic determinants for so-called genetic disorders, and it is possible to duplicate many elements of recognized human neurodegenerative disorders in either knock-in or knock-out mice. However, there are similarly, many identifiable environmental influences on outcomes of the genetic defects; and the course of a progressive neurodegenerative disorder can be greatly modified by environmental elements. Constituent cellular defense mechanisms responsive to the challenge of increased reactive oxygen species represent only one crossroad whereby environment can influence genetic predisposition. In this paper we highlight some of the major neurodegenerative disorders and discuss possible links of gene-environment interplay. The process of adult neurogenesis in brain is also presented as an additional element that influences gene-environment interplay. And the so-called priming processes (i.e., production of receptor supersensitization by repeated drug dosing), is introduced as yet another process that influences how genes and environment ultimately and co-dependently govern behavioral ontogeny and outcome. In studies attributing the influence of genetic alteration on behavioral phenotypy, it is essential to carefully control environmental influences.