Juvenile Huntington's disease presenting as progressive myoclonic epilepsy

Clinical Review of Juvenile Huntington's Disease

 Juvenile Huntington's disease (JHD) is rare. In the first decade of life speech difficulties, rigidity, and dystonia are common clinical motor symptoms, whereas onset in the second decade motor symptoms may sometimes resemble adult-onset Huntington's disease (AOHD). Cognitive decline is mostly detected by declining school performances. Behavioral symptoms in general do not differ from AOHD but may be confused with autism spectrum disorder or attention deficit hyperactivity disorder and lead to misdiagnosis and/or diagnostic delay. JHD specific features are epilepsy, ataxia, spasticity, pain, itching, and possibly liver steatosis. Disease progression of JHD is faster compared to AOHD and the disease duration is shorter, particularly in case of higher CAG repeat lengths. The diagnosis is based on clinical judgement in combination with a positive family history and/or DNA analysis after careful consideration. Repeat length in JHD is usually >  55 and caused by anticipation, usually via paternal transmission. There are no pharmacological and multidisciplinary guidelines for JHD treatment. Future perspectives for earlier diagnosis are better diagnostic markers such as qualitative MRI and neurofilament light in serum.

Juvenile Huntington's disease masquerading as progressive myoclonus epilepsy

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Juvenile Huntington’s Disease (JHD) seizure can be presenting feature.

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Seizures are common in patients with JHD than adult onset HD and more difficult to treat.

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The EEG varies from normal EEG to generalized spike polyspike wave discharges, focal or multifocal discharges as well as paroxysmal slowing.

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In patients with progressive myoclonic epilepsy, differential diagnosis of Juvenile Huntington’s disease should be considered.

Juvenile Huntington’s disease (JHD) has an onset before 20 years of age, and is characterized by behavioural issues, epilepsy, rigidity, bradykinesia and dystonia. It contributes to 0.5–5% of all Huntington disease (HD) cases. JHD demonstrates a more rapid progression and is characterised by dystonia, as opposed to the slow progression with predominant chorea seen in adult-onset HD. Seizures are described in 38% of JHD as compared to 2% in the adult onset HD. The different types of seizures reported in JHD are generalized seizures, myoclonus, absence seizures and less commonly tonic and focal seizures with impaired awareness. JHD patients have good seizure control initially and develop drug-resistant epilepsy in the later stages of the disease which is rarely reported. Here, we report the case of a 13 -year-old boy, who initially presented with generalized tonic-clonic seizures followed by myoclonic jerks, with subsequent cognitive decline, ataxia, involuntary movements and drug resistant epilepsy mimicking a progressive myoclonus sepilepsy. His EEG changed from normal background with generalized interictal epileptiform discharges to diffuse slowing with fast activity devoid of epileptiform activity to reflect electroclinical evolution of the disease process.

The Role of the Cerebellum in Huntington's Disease: a Systematic Review

Huntington's disease (HD) is a rare neurological disorder characterized by progressive motor, cognitive, and psychiatric disturbances. Although striatum degeneration might justify most of the motor symptoms, there is an emerging evidence of involvement of extra-striatal structures, such as the cerebellum. To elucidate the cerebellar involvement and its afferences with motor, psychiatric, and cognitive symptoms in HD. A systematic search in the literature was performed in MEDLINE, LILACS, and Google Scholar databases. The research was broadened to include the screening of reference lists of review articles for additional studies. Studies available in the English language, dating from 1993 through May 2020, were included. Clinical presentation of patients with HD may not be considered as the result of an isolated primary striatal dysfunction. There is evidence that cerebellar involvement is an early event in HD and may occur independently of striatal degeneration. Also, the loss of the compensation role of the cerebellum in HD may be an explanation for the clinical onset of HD. Although more studies are needed to elucidate this association, the current literature supports that the cerebellum may integrate the natural history of neurodegeneration in HD.

Clinical Manifestation of Juvenile and Pediatric HD Patients: A Retrospective Case Series

BACKGROUND

Studies on the clinical manifestation and course of disease in children suffering from Huntington's disease (HD) are rare. Case reports of juvenile HD (onset ≤ 20 years) describe heterogeneous motoric and non-motoric symptoms, often accompanied with a delay in diagnosis. We aimed to describe this rare group of patients, especially with regard to socio-medical aspects and individual or common treatment strategies. In addition, we differentiated between juvenile and the recently defined pediatric HD population (onset < 18 years).

METHODS

Out of 2593 individual HD patients treated within the last 25 years in the Huntington Centre, North Rhine-Westphalia (NRW), 32 subjects were analyzed with an early onset younger than 21 years (1.23%, juvenile) and 18 of them younger than 18 years of age (0.69%, pediatric).

RESULTS

Beside a high degree of school problems, irritability or aggressive behavior (62.5% of pediatric and 31.2% of juvenile cases), serious problems concerning the social and family background were reported in 25% of the pediatric cohort. This includes an attempted rape and robbery at the age of 12, as problems caused by the affected children, but also alcohol-dependency in a two-year-old induced by a non-HD affected stepfather. A high degree of suicidal attempts and ideations (31.2% in pediatric and 33.3% in juvenile group) was reported, including drinking of solvents, swallowing razor blades or jumping from the fifth floor with following incomplete paraparesis. Beside dopaminergic drugs for treatment of bradykinesia, benzodiazepines and tetrabenazine for treatment of dystonia, cannabinoids, botulinum toxin injection and deep brain stimulation were used for the improvement of movement disorders, clozapine for the treatment of tremor, and dopa-induced hallucinations and zuclopenthixole for the treatment of severe aggressive behavior.

CONCLUSIONS

Beside abnormalities in behavior from an early age due to HD pathology, children seem to have higher socio-medical problems related to additional burden caused by early affected parents, instable family backgrounds including drug abuse of a parent or multiple changes of partners. Treatment required individualized strategies in many cases.

Clinical Presentation and Features of Juvenile-Onset Huntington's Disease: A Systematic Review

BACKGROUND

Juvenile-onset Huntington's disease (JHD) is defined by onset at the age of 20 or younger and represents approximately 5% of all HD cases. Patients with JHD present with a broad range of symptoms and signs that only overlap partially with adult-onset HD. A greater awareness and understanding of the presentation of JHD would improve the diagnosis and treatment of this condition.

OBJECTIVE

To undertake a systematic review of the literature relating to the clinical features at first presentation of JHD.

METHODS

We searched MEDLINE and EMBASE for all studies describing presenting features of JHD patients, performed quality control, and collated and analysed the data.

RESULTS

We screened 2917 records for eligibility, and included 79 studies (n = 285 individuals) in the analysis. All were case reports and case series, synthesising data from 25 different countries. Thirty-four different clinical features at presentation were identified. Four groups of symptoms or signs were present in more than 15% of cases: behavioural disturbance, falls/gait disturbance, cognitive impairment and parkinsonian features. Where data were available, the median age of onset was 9 years, 52% were female, the mutant HTT allele was transmitted paternally in 80% of cases, and the median CAG repeat length was 64.

CONCLUSIONS

JHD can present with a wide variety of symptoms and signs, with non-motor characteristics being observed most frequently. Greater recognition of these presentations will facilitate early diagnosis and management. Tailored rating scales to score motor, non-motor, and functional impairments specifically in JHD are required to standardise research studies, and are under development.

Developmental origins of cortical hyperexcitability in Huntington's disease: Review and new observations

Huntington's disease (HD), an inherited neurodegenerative disorder that principally affects striatum and cerebral cortex, is generally thought to have an adult onset. However, a small percentage of cases develop symptoms before 20 years of age. This juvenile variant suggests that brain development may be altered in HD. Indeed, recent evidence supports an important role of normal huntingtin during embryonic brain development and mutations in this protein cause cortical abnormalities. Functional studies also demonstrated that the cerebral cortex becomes hyperexcitable with disease progression. In this review, we examine clinical and experimental evidence that cortical development is altered in HD. We also provide preliminary evidence that cortical pyramidal neurons from R6/2 mice, a model of juvenile HD, are hyperexcitable and display dysmorphic processes as early as postnatal day 7. Further, some symptomatic mice present with anatomical abnormalities reminiscent of human focal cortical dysplasia, which could explain the occurrence of epileptic seizures in this genetic mouse model and in children with juvenile HD. Finally, we discuss recent treatments aimed at correcting abnormal brain development.

Alterations in GABAA-Receptor Trafficking and Synaptic Dysfunction in Brain Disorders

GABA_A receptors (GABA_AR) are the major players in fast inhibitory neurotransmission in the central nervous system (CNS). Regulation of GABA_AR trafficking and the control of their surface expression play important roles in the modulation of the strength of synaptic inhibition. Different pieces of evidence show that alterations in the surface distribution of GABA_AR and dysregulation of their turnover impair the activity of inhibitory synapses. A diminished efficacy of inhibitory neurotransmission affects the excitatory/inhibitory balance and is a common feature of various disorders of the CNS characterized by an increased excitability of neuronal networks. The synaptic pool of GABA_AR is mainly controlled through regulation of internalization, recycling and lateral diffusion of the receptors. Under physiological condition these mechanisms are finely coordinated to define the strength of GABAergic synapses. In this review article, we focus on the alteration in GABA_AR trafficking with an impact on the function of inhibitory synapses in various disorders of the CNS. In particular we discuss how similar molecular mechanisms affecting the synaptic distribution of GABA_AR and consequently the excitatory/inhibitory balance may be associated with a wide diversity of pathologies of the CNS, from psychiatric disorders to acute alterations leading to neuronal death. A better understanding of the cellular and molecular mechanisms that contribute to the impairment of GABAergic neurotransmission in these disorders, in particular the alterations in GABA_AR trafficking and surface distribution, may lead to the identification of new pharmacological targets and to the development of novel therapeutic strategies.

Therapeutic effects of stem cells in rodent models of Huntington's disease: Review and electrophysiological findings

The principal symptoms of Huntington's disease (HD), chorea, cognitive deficits, and psychiatric symptoms are associated with the massive loss of striatal and cortical projection neurons. As current drug therapies only partially alleviate symptoms, finding alternative treatments has become peremptory. Cell replacement using stem cells is a rapidly expanding field that offers such an alternative. In this review, we examine recent studies that use mesenchymal cells, as well as pluripotent, cell-derived products in animal models of HD. Additionally, we provide further electrophysiological characterization of a human neural stem cell line, ESI-017, which has already demonstrated disease-modifying properties in two mouse models of HD. Overall, the field of regenerative medicine represents a viable and promising avenue for the treatment of neurodegenerative disorders including HD.

Teenage-onset progressive myoclonic epilepsy due to a familial C9orf72 repeat expansion

BACKGROUND

The progressive myoclonic epilepsies (PME) are a heterogeneous group of disorders in which a specific diagnosis cannot be made in a subset of patients, despite exhaustive investigation. C9orf72 repeat expansions are emerging as an important causal factor in several adult-onset neurodegenerative disorders, in particular frontotemporal lobar degeneration and amyotrophic lateral sclerosis. An association with PME has not been reported previously.

OBJECTIVE

To identify the causative mutation in a Belgian family where the proband had genetically unexplained PME.

RESULTS

We report a 33-year old woman who had epilepsy since the age of 15 and then developed progressive cognitive deterioration and multifocal myoclonus at the age of 18. The family history suggested autosomal dominant inheritance of psychiatric disorders, epilepsy, and dementia. Thorough workup for PME including whole exome sequencing did not reveal an underlying cause, but a C9orf72 repeat expansion was found in our patient and affected relatives. Brain biopsy confirmed the presence of characteristic p62-positive neuronal cytoplasmic inclusions.

CONCLUSION

C9orf72 mutation analysis should be considered in patients with PME and psychiatric disorders or dementia, even when the onset is in late childhood or adolescence.

Tics as an initial manifestation of juvenile Huntington's disease: case report and literature review

BACKGROUND

Huntington's disease (HD) is an autosomal dominant disorder, typically characterized by chorea due to a trinucleotide repeat expansion in the HTT gene, although the clinical manifestations of patients with juvenile HD (JHD) are atypical.

CASE PRESENTATION

A 17-year-old boy with initial presentation of tics attended our clinic and his DNA analysis demonstrated mutation in the HTT gene (49 CAG repeats). After treatment, his symptoms improved. Furthermore, we performed literature review through searching the databases and summarized clinical features in 33 JHD patients.

CONCLUSION

The most prevalent symptoms are ataxia, and two cases reported that tics as initial and prominent manifestation in JHD. Among them, 88% patients carried CAG repeats beyond 60 and most of them have family history. This case here illustrates the variable range of clinical symptoms of JHD and the necessity of testing for the HD mutation in young patients with tics with symptoms unable to be explained by Tourette's syndrome (TS).

American College of Medical Genetics and Genomics Standards and Guidelines for Clinical Genetics Laboratories, 2014 edition: technical standards and guidelines for Huntington disease

Huntington disease is an autosomal-dominant neurodegenerative disease of mid-life onset caused by expansion of a polymorphic trinucleotide (CAG) repeat. Variable penetrance for alleles carrying 36-39 repeats has been noted, but the disease appears fully penetrant when the repeat numbers are >40. An abnormal CAG repeat may expand, contract, or be stably transmitted when passed from parent to child. Assays used to diagnose Huntington disease must be optimized to ensure the accurate and unambiguous quantitation of CAG repeat length. This document provides an overview of Huntington disease and methodological considerations for Huntington disease testing. Examples of laboratory reports are also included.

Managing juvenile Huntington's disease

Huntington's disease (HD) is a well-recognized progressive neurodegenerative disorder that follows an autosomal dominant pattern of inheritance. Onset is insidious and can occur at almost any age, but most commonly the diagnosis is made between the ages of 35 and 55 years. Onset ≤20 years of age is classified as juvenile HD (JHD). This age-based definition is arbitrary but remains convenient. There is overlap between the clinical pathological and genetic features seen in JHD and more traditional adult-onset HD. Nonetheless, the frequent predominance of bradykinesia and dystonia early in the course of the illness, more frequent occurrence of epilepsy and myoclonus, more widespread pathology, and larger genetic lesion means that the distinction is still relevant. In addition, the relative rarity of JHD means that the clinician managing the patient is often doing so for the first time. Management is, at best, symptomatic and supportive with few or no evidence-based guidelines. In this article, the authors will review what is known of the condition and present some suggestions based on their experience.

Myoclonus and epilepsy

Epileptic myoclonus can be defined as an elementary electroclinical manifestation of epilepsy involving descending neurons, whose spatial (spread) or temporal (self-sustained repetition) amplification can trigger overt epileptic activity and can be classified as cortical (positive and negative), secondarily generalized, thalamo-cortical, and reticular. Cortical epileptic myoclonus represents a fragment of partial or symptomatic generalized epilepsy; thalamo-cortical epileptic myoclonus is a fragment of idiopathic generalized epilepsy. Reflex reticular myoclonus represents the clinical counterpart of fragments of hypersynchronous epileptic activity of neurons in the brainstem reticular formation. Epileptic myoclonus, in the setting of an epilepsy syndrome, can be only one component of a seizure, the only seizure manifestations, one of the multiple seizure types or a more stable condition that is manifested in a nonparoxysmal fashion and mimics a movement disorder. This complex correlation is more obvious in patients with epilepsia partialis continua in which cortical myoclonus and overt focal motor seizures usually start in the same somatic (and cortical) region. In patients with cortical tremor this correlation is less obvious and requires neurophysiological studies to be demonstrated.

Huntington's disease in children

Huntington's disease (HD) is a dominantly inherited, fatal neurodegenerative disease. This incurable illness is characterized by a triad of a movement disorder, cognitive decline and psychiatric manifestations. Although most patients with HD have disease onset in the adult years, a small but significant proportion present with pediatric HD. It has been long known that patients with early-onset HD commonly exhibit prominent parkinsonism, known as the Westphal variant of HD. However, even among patients with pediatric HD there are differential clinical features depending on the age of onset, with younger patients frequently presenting diagnostic challenges. In his chapter, the characteristics of patients with childhood- and adolescence-onset HD are discussed, focusing on the differential clinical features that can aid the clinical reach a correct diagnosis, the indications and rational use of genetic testing and the currently available options for symptomatic treatment.

Clinical neurophysiology in movement disorders

Neurophysiological tools are very helpful in characterizing various movement disorders, consequently guiding etiological research and therapy. Movement disorders recordings are currently underutilized in neurological practice in adults and could also be extended to the pediatric population. Surface polymyography (EMG) combined with accelerometry is commonly used for the analysis of many types of hyperkinetic movement disorders, mainly myoclonus, tremor, dystonia, and sometimes tics and chorea. To study myoclonus, techniques exploring cortical excitability, namely conventional EEG, EEG-jerk-locked-back-averaging (JLBA), somatosensory evoked potentials (SEP) and C-reflex studies, should necessarily complete the EMG analysis. Premovement potential recording and measures of the stimulus induced jerks latencies may help to differentiate psychogenic jerks from myoclonus. The field of clinical usefulness of movement disorders recordings is large. Main issues are: (1) to differentiate tremor from myoclonus, (2) to demonstrate and locate dystonic features, either isolated or associated to tremor and myoclonus, (3) to define the nature of a tremor, (4) to assess the psychogenic nature of a tremor or jerks, and (5) to define the neurophysiological generator of myoclonus in the central nervous system. Neurophysiological data allow us to clearly classify myoclonus as cortical, cortico-thalamic, and subcortical-resulting from lesions or dysfunctions of basal ganglia/reticular system-or spinal.

Juvenile Huntington's disease presenting as difficult-to-treat seizure and the first episode of psychosis

OBJECTIVE

The objective was to describe a case of juvenile Huntington's disease that first presented with seizures and psychosis.

METHODS

A male patient with no history of epilepsy and psychiatric disorder had his first seizure at the age of 20 years, which was followed by 3 years of psychotic disorder.

RESULTS

Laboratory investigations were normal, and mild diffuse cortical atrophy was detected using magnetic resonance imaging. Both the seizures and psychosis were difficult to treat. Three years later, chorea and personality changes appeared. Genetic tests revealed an expanded allele with 60 CAG repeats, confirming the typical Huntington's disease characteristic.

CONCLUSION

Patients with difficult-to-treat seizures and the first episode of psychosis should be considered for the diagnosis of juvenile Huntington's disease.

Disrupted GABAAR trafficking and synaptic inhibition in a mouse model of Huntington's disease

Growing evidence suggests that Huntington's disease (HD), a neurodegenerative movement disorder caused by the mutant huntingtin (htt) with an expanded polyglutamine (polyQ) repeat, is associated with the altered intracellular trafficking and synaptic function. GABA(A) receptors, the key determinant of the strength of synaptic inhibition, have been found to bind to the huntingtin associated protein 1 (HAP1). HAP1 serves as an adaptor linking GABA(A) receptors to the kinesin family motor protein 5 (KIF5), controlling the transport of GABA(A) receptors along microtubules in dendrites. In this study, we found that GABA(A)R-mediated synaptic transmission is significantly impaired in a transgenic mouse model of HD expressing polyQ-htt, which is accompanied by the diminished surface expression of GABA(A) receptors. Moreover, the GABA(A)R/HAP1/KIF5 complex is disrupted and dissociated from microtubules in the HD mouse model. These results suggest that GABA(A)R trafficking and function is impaired in HD, presumably due to the interference of KIF5-mediated microtubule-based transport of GABA(A) receptors. The diminished inhibitory synaptic efficacy could contribute to the loss of the excitatory/inhibitory balance, leading to increased neuronal excitotoxicity in HD.

A critical window of CAG repeat-length correlates with phenotype severity in the R6/2 mouse model of Huntington's disease

The R6/2 mouse is the most frequently used model for experimental and preclinical drug trials in Huntington's disease (HD). When the R6/2 mouse was first developed, it carried exon 1 of the huntingtin gene with ~150 cytosine-adenine-guanine (CAG) repeats. The model presented with a rapid and aggressive phenotype that shared many features with the human condition and was particularly similar to juvenile HD. However, instability in the CAG repeat length due to different breeding practices has led to both decreases and increases in average CAG repeat lengths among colonies. Given the inverse relationship in human HD between CAG repeat length and age at onset and to a degree, the direct relationship with severity of disease, we have investigated the effect of altered CAG repeat length. Four lines, carrying ~110, ~160, ~210, and ~310 CAG repeats, were examined using a battery of tests designed to assess the basic R6/2 phenotype. These included electrophysiological properties of striatal medium-sized spiny neurons, motor activity, inclusion formation, and protein expression. The results showed an unpredicted, inverted "U-shaped" relationship between CAG repeat length and phenotype; increasing the CAG repeat length from 110 to 160 exacerbated the R6/2 phenotype, whereas further increases to 210 and 310 CAG repeats greatly ameliorated the phenotype. These findings demonstrate that the expected relationship between CAG repeat length and disease severity observed in humans is lost in the R6/2 mouse model and highlight the importance of CAG repeat-length determination in preclinical drug trials that use this model.

Huntington's Disease and Striatal Signaling

Huntington’s Disease (HD) is the most frequent neurodegenerative disease caused by an expansion of polyglutamines (CAG). The main clinical manifestations of HD are chorea, cognitive impairment, and psychiatric disorders. The transmission of HD is autosomal dominant with a complete penetrance. HD has a single genetic cause, a well-defined neuropathology, and informative pre-manifest genetic testing of the disease is available. Striatal atrophy begins as early as 15 years before disease onset and continues throughout the period of manifest illness. Therefore, patients could theoretically benefit from therapy at early stages of the disease. One important characteristic of HD is the striatal vulnerability to neurodegeneration, despite similar expression of the protein in other brain areas. Aggregation of the mutated Huntingtin (HTT), impaired axonal transport, excitotoxicity, transcriptional dysregulation as well as mitochondrial dysfunction, and energy deficits, are all part of the cellular events that underlie neuronal dysfunction and striatal death. Among these non-exclusive mechanisms, an alteration of striatal signaling is thought to orchestrate the downstream events involved in the cascade of striatal dysfunction.

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.

Genetic mouse models of Huntington's disease: focus on electrophysiological mechanisms

The discovery of the HD (Huntington’s disease) gene in 1993 led to the creation of genetic mouse models of the disease and opened the doors for mechanistic studies. In particular, the early changes and progression of the disease could be followed and examined systematically. The present review focuses on the contribution of these genetic mouse models to the understanding of functional changes in neurons as the HD phenotype progresses, and concentrates on two brain areas: the striatum, the site of most conspicuous pathology in HD, and the cortex, a site that is becoming increasingly important in understanding the widespread behavioural abnormalities. Mounting evidence points to synaptic abnormalities in communication between the cortex and striatum and cell–cell interactions as major determinants of HD symptoms, even in the absence of severe neuronal degeneration and death.

Alterations in cortical excitation and inhibition in genetic mouse models of Huntington's disease

Previously, we identified progressive alterations in spontaneous EPSCs and IPSCs in the striatum of the R6/2 mouse model of Huntington's disease (HD). Medium-sized spiny neurons from these mice displayed a lower frequency of EPSCs, and a population of cells exhibited an increased frequency of IPSCs beginning at approximately 40 d, a time point when the overt behavioral phenotype begins. The cortex provides the major excitatory drive to the striatum and is affected during disease progression. We examined spontaneous EPSCs and IPSCs of somatosensory cortical pyramidal neurons in layers II/III in slices from three different mouse models of HD: the R6/2, the YAC128, and the CAG140 knock-in. Results revealed that spontaneous EPSCs occurred at a higher frequency, and evoked EPSCs were larger in behaviorally phenotypic mice whereas spontaneous IPSCs were initially increased in frequency in all models and subsequently decreased in R6/2 mice after they displayed the typical R6/2 overt behavioral phenotype. Changes in miniature IPSCs and evoked IPSC paired-pulse ratios suggested altered probability of GABA release. Also, in R6/2 mice, blockade of GABA(A) receptors induced complex discharges in slices and seizures in vivo at all ages. In conclusion, altered excitatory and inhibitory inputs to pyramidal neurons in the cortex in HD appear to be a prevailing deficit throughout the development of the disease. Furthermore, the differences between synaptic phenotypes in cortex and striatum are important for the development of future therapeutic approaches, which may need to be targeted early in the development of the phenotype.

A patient with early onset Huntington disease and severe cerebellar atrophy

We report on a girl with early onset Huntington disease (HD). Her initial symptoms at 2 years of age included oral motor dysfunction and gait disturbance. Magnetic resonance imaging of the head revealed severe atrophy of both the vermis and the cerebellar cortex in addition to the common findings of basal ganglia including the caudate nuclei, putamen, and globus pallidus. Molecular analysis showed 160 CAG repeats in the HD gene. This mutation was inherited from her mother who was also affected, with a HD CAG expansion of 60 repeats. Cerebellar symptoms should be considered as a manifestation of early onset HD.

CAG repeat lengths > or =335 attenuate the phenotype in the R6/2 Huntington's disease transgenic mouse

With spontaneous elongation of the CAG repeat in the R6/2 transgene to > or =335, resulting in a transgene protein too large for passive entry into nuclei via the nuclear pore, we observed an abrupt increase in lifespan to >20 weeks, compared to the 12 weeks common in R6/2 mice with 150 repeats. In the > or =335 CAG mice, large ubiquitinated aggregates of mutant protein were common in neuronal dendrites and perikaryal cytoplasm, but intranuclear aggregates were small and infrequent. Message and protein for the > or =335 CAG transgene were reduced to one-third that in 150 CAG R6/2 mice. Neurological and neurochemical abnormalities were delayed in onset and less severe than in 150 CAG R6/2 mice. These findings suggest that polyQ length and pathogenicity in Huntington's disease may not be linearly related, and pathogenicity may be less severe with extreme repeats. Both diminished mutant protein and reduced nuclear entry may contribute to phenotype attenuation.

Huntington disease in a 9-year-old boy: clinical course and neuropathologic examination

Huntington disease is a dominantly inherited, neurodegenerative disorder, usually with onset in the fourth to fifth decade of life but in a small proportion of patients before the age of 20 years. The early-onset form, juvenile Huntington disease, is clinically different from that of more common adult-onset forms and includes cognitive decline, parkinsonism, myoclonus, and seizures. We report a case of a boy with juvenile Huntington disease with a very early age at disease onset (3 years). The suspected clinical diagnosis was confirmed by DNA analysis, which revealed (CAG)(n) expansion into the range characteristic of juvenile Huntington disease (95 repeats). The clinical course of the disease was typical for the juvenile form of Huntington disease, but the diagnosis was not so obvious because there was no history of any neurodegenerative disorder in the family. The child died at the age of 11 years. The detailed neuropathologic investigations performed postmortem showed the characteristic features of Huntington disease. As the patient's de novo mutation was very unlikely to occur, genetic counseling and the possibility of predictive testing were proposed to the family. Indirect molecular data indicate the familial character of the disease, with strong anticipation of transmission.

Juvenile Huntington's disease: does a dosage-effect pathogenic mechanism differ from the classical adult disease?

Huntington's disease (HD) is caused by a CAG repeat mutation translating as a polyglutamine (poly(Q)) expansion in the huntingtin protein, whose main pathogenic mechanism is a gain of toxic function. In the case of large expansions beyond 60 repeats onset may result in juvenile HD (JHD, onset before 20 years of age). However, the triplet number does not represent the only onset modifier even in case of large expansions, mechanisms other than the size of the mutation contribute to the phenotype. In this review we discuss the possibility that some of the pathogenic mechanisms contributing to age at onset and progression may differ in the early onset HD compared with the classical adult pathology.

Progressive myoclonic epilepsies: a review of genetic and therapeutic aspects

The progressive myoclonic epilepsies (PMEs) are a group of symptomatic generalised epilepsies caused by rare disorders, most of which have a genetic component, a debilitating course, and a poor outcome. Challenges with PME arise from difficulty with diagnosis, especially in the early stages of the illness, and further problems of management and drug treatment. Recent advances in molecular genetics have helped achieve better understanding of the different disorders that cause PME. We review the PMEs with emphasis on updated genetics, diagnosis, and therapeutic options.

Case of maternally transmitted juvenile Huntington's disease with a very large trinucleotide repeat

We describe and present a video of a patient with maternally inherited juvenile Huntington's disease (HD) caused by a very large (108-repeat) expansion. Maternally transmitted very large trinucleotide repeats (>100) are extremely rare in juvenile HD and may represent instability during female gametogenesis.

Early onset Huntington disease: a neuronal degeneration syndrome

Huntington disease (HD) is an autosomal dominant, lethal neurodegenerative disorder of the central nervous system, caused by an uncontrolled expansion of a CAG dynamic mutation in the coding region of the IT15gene. Although a majority of patients have a midlife onset of the disease, in a small number of patients the disease manifests before 20 years of age. In adults, HD is mainly characterised by involuntary movements, personality changes and dementia. By contrast, in children a dominant picture of bradykinesia, rigidity, dystonia and epileptic seizures is noticed. The earlier onset is often associated with a paternal transmission of the disease allele to the offspring. We report here a rather unusual infantile onset of the disease in a little girl who presented with a history of seizures and psychomotor regression starting at the age of 3 years. A progressive cortical-subcortical atrophy, progressive cerebellar atrophy and lesions in the basal ganglia were found on MRI. An important expansion, of 214 triplet numbers, of the CAG repeat size associated with HD, was observed.

CONCLUSION

Juvenile Huntingdon disease should be considered in children suffering from a progressive neurodegenerative disease.

Technical standards and guidelines for Huntington disease testing

One mission of the ACMG Laboratory Quality Assurance (QA) Committee is to develop standards and guidelines for clinical genetics laboratories, including cytogenetics, biochemical, and molecular genetics specialties. This document was developed under the auspices of the Molecular Subcommittee of the Laboratory QA Committee by the Huntington Disease (HD) Working Group. These guidelines are not to be interpreted as restrictive or the only approach but to provide a helpful guide. Certainly, appropriately trained and credentialed laboratory directors have flexibility to utilize various testing platforms and design testing strategies with considerable latitude. We felt that it was essential to include technique-specific guidelines of several current technologies commonly used in laboratories providing HD testing, because the technologies discussed are available commercially and are widely utilized. We take the view that these technologies may change, and thus this document may change with future review.

Huntington's disease: present treatments and future therapeutic modalities

Huntington's disease (HD) is a devastating neuropsychiatric disorder for which therapeutic interventions have been rather fruitless to date, except in a slight symptomatic relief. Even the discovery of the gene related to HD in 1993 has not effectively advanced treatments. This article is essentially a review of available double-blind, placebo-controlled trials of therapy for this condition which also includes relevant open label trials. Unfortunately, HD research has tended to concentrate on the motor aspects of the disorder, whereas the major problems are behavioural (e.g. dementia, depression, psychosis), and the chorea is often least relevant in terms of management. We conclude that there is definitely poor evidence in management of HD. The analysis of the 24 best studies fails to result in a treatment recommendation of clinical relevance. Based on data of open-label studies, or even case reports, we recommend riluzole, olanzapine and amantadine for the treatment of the movement disorders associated with HD, selective serotonin reuptake inhibitors and mirtazapine for the treatment of depression, and atypical antipsychotic drugs for HD psychosis and behavioural problems. Moreover, adjuvant psychotherapy, physiotherapy and speech therapy should be applied to supply the optimal management. Finally, some cellular mechanisms are discussed in this paper because they are essential for future neuroprotective modalities, such as minocycline, unsaturated fatty acids or riluzole.

XL PCR for the detection of large trinucleotide expansions in juvenile Huntington's disease

Juvenile Huntington's disease (HD) becomes clinically manifest before 20 years of age. The diagnosis of HD is based on family history, characteristic clinical findings, and the detection of an expansion of a CAG polyglutamine tract in the Huntingtin gene. Juvenile HD is characterized by paternal anticipation and large CAG expansions that may be missed using routine molecular analysis. We have developed an easy, rapid, and reliable modified PCR method using XL (Extra Long) PCR that allowed us to diagnose one of the youngest children reported with juvenile HD. Without this innovation we would not have been able to demonstrate the large CAG expansion. This assay could become part of a standard protocol for HD testing in molecular diagnostic laboratories.

Cortical myoclonus in children

Cortical myoclonus is a distinct clinical condition that can be defined electrophysiologically, and occurs in both children and adults. It is well known that patients sometimes exhibit stimulus-sensitive jerks and giant somatosensory-evoked potentials (SEPs). In contrast, imaging abnormalities are less prominent in many patients. Reports focusing on cortical myoclonus, except for epilepsia partialis continua, in childhood have been limited in Japan. One reason for this could be that Japanese pediatric neurologists are not familiar with the backaveraging technique. We describe the clinical and physiological features of cortical myoclonus in ten children. Routine EEG, EEG backaveraging, SEP measurement, CT/MRI (computed tomography/magnetic resonance imaging), and TMS (transcranial magnetic stimulation) were performed. All patients exhibited clear evidence of cortical myoclonus. In six patients, backaveraging was necessary since spikes were absent on routine EEG. A cortical source of the myoclonus was further supported by a TMS study performed on four patients. The etiologies of the myoclonus were diverse, cerebrovascular disease being the most common (three patients). Stimulus-sensitive or action-induced jerks were observed in three patients. Cortical SEPs were enlarged in one patient, and reduced or absent in six. Lesions were found on CT/MRI in nine patients, in five of whom the margin of the lesion was within, or adjacent to, the sensorimotor cortex. Complete destruction of the sensorimotor cortex was not observed. It was suggested that cortical neurons in the vicinity of a lesion, rather than in the lesion itself, play a role in the generation of focal myoclonus.