Exclusion of mutations in the PRNP, JPH3, TBP, ATN1, CREBBP, POU3F2 and FTL genes as a cause of disease in Portuguese patients with a Huntington-like phenotype

Genetic screening for Huntington disease phenocopies in Sweden: A tertiary center case series focused on short tandem repeat (STR) disorders

OBJECTIVE

To perform a screening for Huntington disease (HD) phenocopies in a Swedish cohort.

METHODS

Seventy-three DNA samples negative for HD were assessed at a tertiary center in Stockholm. The screening included analyses for C9orf72-frontotemporal dementia/amyotrophic lateral sclerosis (C9orf72-FTD/ALS), octapeptide repeat insertions (OPRIs) in PRNP associated with inherited prion diseases (IPD), Huntington's disease-like 2 (HDL2), spinocerebellar ataxia-2 (SCA2), spinocerebellar ataxia 3 (SCA3) and spinocerebellar ataxia-17 (SCA17). Targeted genetic analysis was carried out in two cases based on the salient phenotypic features.

RESULTS

The screening identified two patients with SCA17, one patient with IPD associated with 5-OPRI but none with nucleotide expansions in C9orf72 or for HDL2, SCA2 or SCA3. Furthermore, SGCE-myoclonic-dystonia 11 (SGCE-M-D) and benign hereditary chorea (BHC) was diagnosed in two sporadic cases. WES identified VUS in STUB1 in two patients with predominant cerebellar ataxia.

CONCLUSIONS

Our results are in keeping with previous screenings and suggest that other genes yet to be discovered are involved in the etiology of HD phenocopies.

Neurodegenerative Diseases: From Dysproteostasis, Altered Calcium Signalosome to Selective Neuronal Vulnerability to AAV-Mediated Gene Therapy

Despite intense research into the multifaceted etiology of neurodegenerative diseases (ND), they remain incurable. Here we provide a brief overview of several major ND and explore novel therapeutic approaches. Although the cause (s) of ND are not fully understood, the accumulation of misfolded/aggregated proteins in the brain is a common pathological feature. This aggregation may initiate disruption of Ca⁺⁺ signaling, which is an early pathological event leading to altered dendritic structure, neuronal dysfunction, and cell death. Presently, ND gene therapies remain unidimensional, elusive, and limited to modifying one pathological feature while ignoring others. Considering the complexity of signaling cascades in ND, we discuss emerging therapeutic concepts and suggest that deciphering the molecular mechanisms involved in dendritic pathology may broaden the phenotypic spectrum of ND treatment. An innovative multiplexed gene transfer strategy that employs silencing and/or over-expressing multiple effectors could preserve vulnerable neurons before they are lost. Such therapeutic approaches may extend brain health span and ameliorate burdensome chronic disease states.

Huntington's disease: lessons from prion disorders

Decades of research on the prion protein and its associated diseases have caused a paradigm shift in our understanding of infectious agents. More recent years have been marked by a surge of studies supporting the application of these findings to a broad array of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Here, we present evidence to suggest that Huntington's disease, a monogenic disorder of the central nervous system, shares features with prion disorders and that, it too, may be governed by similar mechanisms. We further posit that these similarities could suggest that, like other common neurodegenerative disorders, sporadic forms of Huntington's disease may exist.

Loci-specific differences in blood DNA methylation in HBV-negative populations at risk for hepatocellular carcinoma development

Late onset of clinical symptoms in hepatocellular carcinoma (HCC) results in late diagnosis and poor disease outcome. Approximately 85% of individuals with HCC have underlying liver cirrhosis. However, not all cirrhotic patients develop cancer. Reliable tools that would distinguish cirrhotic patients who will develop cancer from those who will not are urgently needed. We used the Illumina HumanMethylation450 BeadChip microarray to test whether white blood cell DNA, an easily accessible source of DNA, exhibits site-specific changes in DNA methylation in blood of diagnosed HCC patients (post-diagnostic, 24 cases, 24 controls) and in prospectively collected blood specimens of HCC patients who were cancer-free at blood collection (pre-diagnostic, 21 cases, 21 controls). Out of 22 differentially methylated loci selected for validation by pyrosequencing, 19 loci with neighbouring CpG sites (probes) were confirmed in the pre-diagnostic study group and subjected to verification in a prospective cirrhotic cohort (13 cases, 23 controls). We established for the first time 9 probes that could distinguish HBV-negative cirrhotic patients who subsequently developed HCC from those who stayed cancer-free. These probes were identified within regulatory regions of BARD1, MAGEB3, BRUNOL5, FXYD6, TET1, TSPAN5, DPPA5, KIAA1210, and LSP1. Methylation levels within DPPA5, KIAA1210, and LSP1 were higher in prospective samples from HCC cases vs. cirrhotic controls. The remaining probes were hypomethylated in cases compared with controls. Using blood as a minimally invasive material and pyrosequencing as a straightforward quantitative method, the established probes have potential to be developed into a routine clinical test after validation in larger cohorts.

Pathogenic insights from Huntington's disease-like 2 and other Huntington's disease genocopies

PURPOSE OF REVIEW

Huntington's disease-like 2 (HDL2) is a rare, progressive, autosomal dominant neurodegenerative disorder that genetically, clinically, and pathologically closely resembles Huntington's disease. We review HDL2 pathogenic mechanisms and examine the implications of these mechanisms for Huntington's disease and related diseases.

RECENT FINDINGS

HDL2 is caused by a CTG/CAG repeat expansion in junctophilin-3. Available data from cell and animal models and human brain suggest that HDL2 is a complex disease in which transcripts and proteins expressed bidirectionally from the junctophilin-3 locus contribute to pathogenesis through both gain-and loss-of-function mechanisms. Recent advances indicate that the pathogenesis of Huntington's disease is equally complex, despite the emphasis on toxic gain-of-function properties of the mutant huntingtin protein.

SUMMARY

Studies examining in parallel the genetic, clinical, neuropathological, and mechanistic similarities between Huntington's disease and HDL2 have begun to identify points of convergence between the pathogenic pathways of the two diseases. Comparisons to other diseases that are phenotypically or genetically related to Huntington's disease and HDL2 will likely reveal additional common pathways. The ultimate goal is to identify shared therapeutic targets and eventually develop therapies that may, at least in part, be effective across multiple similar rare diseases, an essential approach given the scarcity of resources for basic and translational research.

Recent advances in genetics of chorea

PURPOSE OF REVIEW

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.

RECENT FINDINGS

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.

SUMMARY

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.

Huntington's Disease, Huntington's Disease Look-Alikes‎, and Benign Hereditary Chorea: What's New?

Background

The differential diagnosis of chorea syndromes is complex. It includes inherited forms, the most common of which is autosomal dominant Huntington's disease (HD). In addition, there are disorders mimicking HD, the so-called HD-like (HDL) syndromes.

Methods and Results

Here we review main clinical, genetic, and pathophysiological characteristics of HD and the rare HD phenocopies in order to familiarize clinicians with them. Molecular studies have shown that HD phenocopies account for about 1% of suspected HD cases, most commonly due to mutations in C9orf72 (also the main cause of frontotemporal dementia and amyotrophic lateral sclerosis syndromes), TATA box-binding protein (spinocerebellar ataxia type 17 [SCA17]/HDL4), and JPH3 (HDL2). Systematic screening studies also revealed mutations in PRNP (prion disease), VPS13A (chorea-acanthocytosis), ATXN8OS-ATXN8 (SCA8), and FXN (late-onset Friedreich's Ataxia) in single cases. Further differential diagnoses to consider in patients presenting with a clinical diagnosis consistent with HD, but without the HD expansion, include dentatorubral-pallidoluysian atrophy and benign hereditary chorea (TITF1), as well as the recently described form of ADCY5-associated neurodegeneration. Lastly, biallelic mutations in RNF216 and FRRS1L have recently been reported as autosomal recessive phenocopies of HD.

Conclusion

There is a growing list of genes associated with chorea, yet a substantial percentage of patients remain undiagnosed. It is likely that more genes will be discovered in the future and that the clinical spectrum of the described disorders will broaden.

A multidimensional approach to an in-depth proteomics analysis of transcriptional regulators in neuroblastoma cells

The dynamic regulation of transcriptional events is fundamental to many aspects of neuronal cell functions. However, proteomics methods have not been routinely used in global neuroproteomics analyses of transcriptional regulators because they are much less abundant than the "house-keeping" proteins in cells and tissues. Recent improvements in both biochemical preparations of nuclear proteins and detection sensitivities of proteomics technologies have made the global analysis of nuclear transcriptional regulators possible. We report here an optimised neuroproteomic method for the analysis of transcriptional regulators in the nuclear extracts of SHSY-5Y neuroblastoma cells by combining an improved nuclear protein extraction procedure with multidimensional peptide separation approaches. We found that rigorous removal of cytoplasmic proteins and solubilisation of DNA-associated proteins improved the number of nuclear proteins identified. Furthermore, we discovered that multidimensional peptide separations by either strong cation exchange (SCX) chromatography or electrostatic repulsion-hydrophilic interaction chromatography (ERLIC) analysis detected more than 1800 nuclear proteins, which constitutes one of the largest datasets of nuclear proteins reported for a neuronal cell. Thus, in-depth analysis of transcriptional regulators for studying neurological diseases are increasingly feasible.

Genetic screening of Greek patients with Huntington’s disease phenocopies identifies an SCA8 expansion

Huntington’s disease (HD) is an autosomal dominant disorder characterized by a triad of chorea, psychiatric disturbance and cognitive decline. Around 1% of patients with HD-like symptoms lack the causative HD expansion and are considered HD phenocopies. Genetic diseases that can present as HD phenocopies include HD-like syndromes such as HDL1, HDL2 and HDL4 (SCA17), some spinocerebellar ataxias (SCAs) and dentatorubral-pallidoluysian atrophy (DRPLA). In this study we screened a cohort of 21 Greek patients with HD phenocopy syndromes formutations causing HDL2, SCA17, SCA1, SCA2, SCA3,SCA8, SCA12 and DRPLA. Fifteen patients (71%) had a positive family history. We identified one patient (4.8% of the total cohort) with an expansion of 81 combined CTA/CTG repeats at the SCA8 locus. This falls within what is believed to be the high-penetrance allele range. In addition to the classic HD triad, the patient had features of dystonia and oculomotor apraxia. There were no cases of HDL2, SCA17, SCA1, SCA2, SCA3, SCA12 or DRPLA. Given the controversy surrounding the SCA8 expansion, the present finding may be incidental. However, if pathogenic, it broadens the phenotype that may be associated with SCA8 expansions. The absence of any other mutations in our cohort is not surprising, given the low probability of reaching a genetic diagnosis in HD phenocopy patients.

Clinical and genetic analysis of 29 Brazilian patients with Huntington's disease-like phenotype

Huntington's disease (HD) is a neurodegenerative disorder characterized by chorea, behavioral disturbances and dementia, caused by a pathological expansion of the CAG trinucleotide in the HTT gene. Several patients have been recognized with the typical HD phenotype without the expected mutation. The objective of this study was to assess the occurrence of diseases such as Huntington's disease-like 2 (HDL2), spinocerebellar ataxia (SCA) 1, SCA2, SCA3, SCA7, dentatorubral-pallidoluysian atrophy (DRPLA) and chorea-acanthocytosis (ChAc) among 29 Brazilian patients with a HD-like phenotype. In the group analyzed, we found 3 patients with HDL2 and 2 patients with ChAc. The diagnosis was not reached in 79.3% of the patients. HDL2 was the main cause of the HD-like phenotype in the group analyzed, and is attributable to the African ancestry of this population. However, the etiology of the disease remains undetermined in the majority of the HD negative patients with HD-like phenotype.

Movement disorders in spinocerebellar ataxias

Autosomal dominant spinocerebellar ataxias (SCAs) can present with a large variety of noncerebellar symptoms, including movement disorders. In fact, movement disorders are frequent in many of the various SCA subtypes, and they can be the presenting, dominant, or even isolated disease feature. When combined with cerebellar ataxia, the occurrence of a specific movement disorder can provide a clue toward the underlying genotype. There are reasons to believe that for some coexisting movement disorders, the cerebellar pathology itself is the culprit, for example, in the case of cortical myoclonus and perhaps dystonia. However, movement disorders in SCAs are more likely related to extracerebellar pathology, and imaging and neuropathological data indeed show involvement of other parts of the motor system (substantia nigra, striatum, pallidum, motor cortex) in some SCA subtypes. When confronted with a patient with an isolated movement disorder, that is, without ataxia, there is currently no reason to routinely screen for SCA gene mutations, the only exceptions being SCA2 in autosomal dominant parkinsonism (particularly in Asian patients) and SCA17 in the case of a Huntington's disease-like presentation without an HTT mutation.

Huntington's disease - clinical signs, symptoms, presymptomatic diagnosis, and diagnosis

HD is a complex illness, with a broad clinical picture that begins years before clear motor onset and evolves over decades to a terminal state of extreme disability. It challenges the resources of families and communities and the skills of medical and ancillary health care providers. A broader understanding of the phenotypes, progression, and genetic basis of HD may elevate the standard of care for these deserving patients.

Huntington's disease look-alikes

Huntington's disease (HD) is caused by a triplet repeat expansion in the IT15 gene on chromosome 4 encoding huntingtin. Gene mutations are found in about 99% of cases, with symptoms and signs suggestive of HD. This implies the existence of other causes of this syndrome, and, in recent years, several other distinct genetic disorders have been identified that can present with a clinical picture indistinguishable from HD, termed HD-like (HDL) syndromes. So far, four genes associated with HDL syndromes have been identified, including the prion protein gene (HDL1), the junctophilin 3 gene (HDL2) and, the gene encoding the TATA box-binding protein (HDL4). In addition, a single family with a recessively inherited HD phenocopy, the exact genetic basis of which is currently unknown (HDL3), has been described. These disorders, however, account for only a small proportion of HDL cases, and the list of HDL genes and conditions is set to grow. In this article, we review the currently identified HD phenocopy disorders and discuss clinical clues to facilitate further investigations. We will concentrate on the four so-called HDL syndromes mentioned above. Other genetic choreatic syndromes such as dentatorubral-pallidoluysian atrophy, neuroferritinopathy, pantothenate kinase-associated neurodegeneration, and chorea-acanthocytosis are also briefly discussed.

Spinocerebellar ataxia 17 (SCA17) and Huntington's disease-like 4 (HDL4)

Spinocerebellar ataxia 17 (SCA17) or Huntington's disease-like-4 is a neurodegenerative disease caused by the expansion above 44 units of a CAG/CAA repeat in the coding region of the TATA box binding protein (TBP) gene leading to an abnormal expansion of a polyglutamine stretch in the corresponding protein. Alleles with 43 and 44 repeats have been identified in sporadic cases and their pathogenicity remains uncertain. Furthermore, incomplete penetrance of pathological alleles with up to 49 repeats has been suggested. The imperfect nature of the repeat makes intergenerational instability extremely rare and de novo mutations are most likely the result of partial duplications. This is one of the rarer forms of autosomal dominant cerebellar ataxia but the associated phenotype is often severe, involving various systems (cerebral cortex, striatum, and cerebellum), with extremely variable age at onset (range: 3-75 years) and clinical presentation. This gene is thought to account for a small proportion of patients with a Huntington's disease-like phenotype and cerebellar signs. Parkinson's disease-like, Creutzfeldt-Jakob disease-like and Alzheimer disease-like phenotypes have also been described with small SCA17 expansions. The abnormal protein is expressed at the same level as its normal counterpart and forms neuronal intranuclear inclusions containing other proteins involved in protein folding or degradation. The increase in the size of the glutamine stretch enhances transcription in vitro, probably leading to transcription deregulation. Interestingly, the TBP protein mutated in SCA17 is recruited in the inclusions of other polyglutaminopathies, suggesting its involvement in the transcription down-regulation observed in these diseases.

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.

The Huntington's disease-like syndromes: what to consider in patients with a negative Huntington's disease gene test

Huntington's disease (HD), which is caused by a triplet-repeat expansion in the IT15 gene (also known as huntingtin or HD), accounts for about 90% of cases of chorea of genetic etiology. In recent years, several other distinct genetic disorders have been identified that can present with a clinical picture indistinguishable from that of HD. These disorders are termed Huntington's disease-like (HDL) syndromes. So far, four such conditions have been recognized, namely disorders attributable to mutations in the prion protein gene (HDL1), the junctophilin 3 gene (HDL2), and the gene encoding the TATA box-binding protein (HDL4/SCA17), and a recessively inherited HD phenocopy in a single family (HDL3), the genetic basis of which is currently poorly understood. These disorders, however, account for only a small proportion of cases with the HD phenotype but a negative genetic test for HD, and the list of HDL genes and conditions is set to grow. In this article, we review the most important HD phenocopy disorders identified to date and discuss the clinical clues that guide further investigation. We will concentrate on the four so-called HDL syndromes mentioned above, as well as other genetic disorders such as dentatorubral-pallidoluysian atrophy, neuroferritinopathy, pantothenate-kinase-associated neurodegeneration and chorea-acanthocytosis.