Huntington Disease in Asia

Clinical and Genetic Characteristics Associated With Survival Outcome in Late-Onset Huntington's Disease in South Korea

BACKGROUND AND PURPOSE

The onset of Huntington's disease (HD) usually occurs before the age of 50 years, and the median survival time from onset is 15 years. We investigated survival in patients with late-onset HD (LoHD) (age at onset ≥60 years) and the associations of the number of mutant CAG repeats and age at onset (AAO) with survival in patients with HD.

METHODS

Patients with genetically confirmed HD at six referral centers in South Korea between 2000 and 2020 were analyzed retrospectively. Baseline demographic, clinical, and genetic characteristics and the survival status as at December 2020 were collected.

RESULTS

Eighty-seven patients were included, comprising 26 with LoHD (AAO=68.77±5.91 years, mean±standard deviation; 40.54±1.53 mutant CAG repeats) and 61 with common-onset HD (CoHD) (AAO=44.12±8.61 years, 44.72±4.27 mutant CAG repeats). The ages at death were 77.78±7.46 and 53.72±10.86 years in patients with LoHD and CoHD, respectively (p<0.001). The estimated survival time was 15.21±2.49 years for all HD patients, and 10.74±1.95 and 16.15±2.82 years in patients with LoHD and CoHD, respectively. More mutant CAG repeats and higher AAO were associated with shorter survival (hazard ratio [HR]=1.05, 95% confidence interval [CI]=1.01-1.09, p=0.019; and HR=1.17, 95% CI=1.03-1.31, p=0.013; respectively) for all HD patients. The LoHD group showed no significant factors associated with survival after disease onset, whereas the number of mutant CAG repeats had a significant effect (HR=1.12, 95% CI=1.01-1.23, p=0.034) in the CoHD group.

CONCLUSIONS

Survival after disease onset was shorter in patients with LoHD than in those with CoHD. More mutant CAG repeats and higher AAO were associated with shorter survival in patients with HD.

Metabolomics: An Emerging "Omics" Platform for Systems Biology and Its Implications for Huntington Disease Research

Huntington's disease (HD) is a progressive, fatal neurodegenerative disease characterized by motor, cognitive, and psychiatric symptoms. The precise mechanisms of HD progression are poorly understood; however, it is known that there is an expansion of the trinucleotide cytosine-adenine-guanine (CAG) repeat in the Huntingtin gene. Important new strategies are of paramount importance to identify early biomarkers with predictive value for intervening in disease progression at a stage when cellular dysfunction has not progressed irreversibly. Metabolomics is the study of global metabolite profiles in a system (cell, tissue, or organism) under certain conditions and is becoming an essential tool for the systemic characterization of metabolites to provide a snapshot of the functional and pathophysiological states of an organism and support disease diagnosis and biomarker discovery. This review briefly highlights the historical progress of metabolomic methodologies, followed by a more detailed review of the use of metabolomics in HD research to enable a greater understanding of the pathogenesis, its early prediction, and finally the main technical platforms in the field of metabolomics.

Pain in Huntington's disease and its potential mechanisms

Pain is common and frequent in many neurodegenerative diseases, although it has not received much attention. In Huntington's disease (HD), pain is often ignored and under-researched because attention is more focused on motor and cognitive decline than psychiatric symptoms. In HD progression, pain symptoms are complex and involved in multiple etiologies, particularly mental issues such as apathy, anxiety and irritability. Because of psychiatric issues, HD patients rarely complain of pain, although their bodies show severe pain symptoms, ultimately resulting in insufficient awareness and lack of research. In HD, few studies have focused on pain and pain-related features. A detailed and systemic pain history is crucial to assess and explore pain pathophysiology in HD. This review provides an overview concentrating on pain-related factors in HD, including neuropathology, frequency, features, affecting factors and mechanisms. More attention and studies are still needed in this interesting field in the future.

The Comprehensive Analysis of Motor and Neuropsychiatric Symptoms in Patients with Huntington's Disease from China: A Cross-Sectional Study

Huntington’s disease (HD) is an autosomal dominant inherited neurodegenerative disorder caused by CAG repeats expansion. There is a paucity of comprehensive clinical analysis in Chinese HD patients due to the low prevalence of HD in Asia. We aimed to comprehensively describe the motor, neuropsychiatric symptoms, and functional assessment in patients with HD from China. A total of 205 HD patients were assessed by the Unified Huntington’s Disease Rating Scale (UHDRS), the short version of Problem-Behavior Assessment (PBA-s), Hamilton Depression Scale (HAMD) and Beck Depression Inventory (BDI). Multivariate logistic regression analysis was used to explore the independent variables correlated with neuropsychiatric subscales. The mean age of motor symptom onset was 41.8 ± 10.0 years old with a diagnostic delay of 4.3 ± 3.8 years and a median CAG repeats of 44. The patients with a positive family history had a younger onset and larger CAG expansion than the patients without a family history (p < 0.05). There was a significant increase in total motor score across disease stages (p < 0.0001). Depression (51%) was the most common neuropsychiatric symptom at all stages, whereas moderate to severe apathy commonly occurred in advanced HD stages. We found lower functional capacity and higher HAMD were independently correlated with irritability; higher HAMD and higher BDI were independently correlated with affect; male sex and higher HAMD were independently correlated with apathy. In summary, comprehensive clinical profile analysis of Chinese HD patients showed not only chorea-like movement, but psychiatric symptoms were outstanding problems and need to be detected early. Our study provides the basis to guide clinical practice, especially in practical diagnostic and management processes.

Spatial proteomic alterations detected via MALDI-MS imaging implicate neuronal loss in a Huntington's disease mouse (YAC128) brain

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder that occurs with the increase of CAG trinucleotide repeats in the huntingtin gene. To understand the mechanisms of HD, powerful proteomics techniques, such as liquid chromatography-tandem mass spectrometry (LC-MS/MS) were employed. However, one major drawback of these methods is loss of the region-specific quantitative information of the proteins due to analysis of total tissue lysates. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is a MS-based label-free technique that works directly on tissue sections and gathers m/z values with their respective regional information. In this study, we established a data processing protocol that includes several software programs and methods to determine spatial protein alterations between the brain samples of a 12 month-old YAC128 HD mouse model and their non-transgenic littermates. 22 differentially expressed proteins were revealed with their respective regional information, and possible relationships of several proteins were discussed. As a validation of the MALDI-MSI analysis, a differentially expressed protein (GFAP) was verified using immunohistochemical staining. Furthermore, since several proteins detected in this study have previously been associated with neuronal loss, neuronal loss in the cortical region was demonstrated using an anti-NeuN immunohistochemical staining method. In conclusion, the findings of this research have provided insights into the spatial proteomic changes between HD transgenic and non-transgenic littermates and therefore, we suggest that MALDI-MSI is a powerful technique to determine spatial proteomic alterations between biological samples, and the data processing that we present here can be employed as a complementary tool for the data analysis.

Sporadic Huntington's disease in the Philippines: a case report

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder with core clinical features of choreoathetosis, cognitive deficits and behavioral changes. It is a rare disorder, primarily affecting the Caucasian population, and rarely Asians. To date, there are only two reported, genetically proven familial HD cases in the Philippines. We present the case of a 39-year-old Filipino male with a 10-year history of progressive behavior and personality changes followed by cognitive decline and choreoathetotic movements. Neuroimaging showed atrophy of both caudate and putamen with putaminal rim sign. Genetic testing revealed a 47 CAG trinucleotide repeats in the Huntingtin gene; family history is negative. This is the first, genetically proven, sporadic and the third HD case in the Philippines. Despite its rarity, this report highlights the importance of including HD as a possible cause of adult-onset chorea among Filipinos.

Huntington's Disease in Israel: A Population-Based Study Using 20 Years of Routinely-Collected Healthcare Data

BACKGROUND

Huntington's disease (HD) is a rare, genetic, neurodegenerative disease. Obtaining population-level data on epidemiology and disease management is challenging.

OBJECTIVE

To investigate the epidemiology, clinical manifestations, treatment, and healthcare utilization of patients with HD in Israel.

METHODS

Retrospective population-based cohort study, including 20 years of routinely collected data from Maccabi Healthcare Services, an insurer and healthcare provider for one-quarter of the Israeli population.

RESULTS

The study cohort included 109 adult patients (aged ≥18 years) diagnosed with HD, with mean age of 49.9 years and 56%females. The most common HD-related conditions were anxiety (40%), behavioral problems (34%), sleep disorders (21%), and falls (13%). Annual incidence rates for HD ranged from 0.17 to 1.34 per 100,000 from 2000 to 2018; the 2018 crude prevalence in adults was 4.36 per 100,000. Median survival from diagnosis was approximately 12 years (95%CI: 10.4-15.3). The most frequent symptomatic treatments were antidepressants (69%), antipsychotics (63%), and tetrabenazine (63%), the only drug approved for the treatment of HD chorea in Israel during the examined period. Patterns of healthcare utilization changed as disease duration increased, reflected by increased frequency of emergency department visits and home visits.

CONCLUSION

This retrospective population-based study provides insights into the prevalence, incidence, clinical profile, survival, and resource utilization of patients with HD in ethnically diverse Israel. The findings in this study are generally consistent with the international literature and demonstrate the value of routinely collected healthcare data as a complementary resource in HD research.

Incidence of Huntington disease in a northeastern Spanish region: a 13-year retrospective study at tertiary care centre

Background

Despite the progress in the knowledge of Huntington disease (HD) in recent years, the epidemiology continues uncertain, so the study of incidence becomes relevant. This is important since various factors (type of population, diagnostic criteria, disease-modifying factors, etc.) make these data highly variable. Therefore, the genetic diagnosis of these patients is important, since it unequivocally allows the detection of new cases.

Methods

Descriptive retrospective study with 179 individuals. Incidence of HD was calculated from the ratio of number of symptomatic cases newly diagnosed per 100,000 inhabitants per year during the period 2007–2019 in Aragon (Spain).

Results

50 (27.9%) incident cases of HD (CAG repeat length ≥ 36) were identified from a total of 179 persons studied. The remaining 129/179 (72.1%) were HD negative (CAG repeat length < 36). 29 (58.0%) females and 21 (42.0%) males were confirmed as HD cases. The overall incidence was 0.648 per 100,000 patient-years. 11/50 positive HD cases (22.0%) were identified by performing a predictive test, without clinical symptoms. The minimum number of CAG repeats found was 9 and the most common CAG length among HD negative individuals was 16.

Conclusions

Our incidence lied within the range reported for other Caucasian populations. Implementation of new techniques has allowed to determine the exact number of CAG repeats, which is especially important in patients with triplet expansions in an HD intermediate and/or incomplete penetrance allele, both in diagnostic, predictive and prenatal tests.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12881-020-01174-z.

Scientific impact of movement disorders research from Southeast Asia: A bibliometric analysis

BACKGROUND

The number of scientific publications on movement disorders from Southeast Asia (SEA) is thought to be low. Thus, we looked at the movement disorders research productivity among SEA countries and its associations with country-specific socioeconomic factors.

METHODS

We performed a systematic search for publications indexed in PubMed, Scopus, Embase and Cochrane Central Register of Controlled Trials from January 2000 to December 2019 with at least one author from SEA. Bibliometric indices were used to evaluate research impact. The country-specific socioeconomic characteristics were also obtained.

RESULTS

Of the 9488 identified articles, 1567 met the eligibility criteria. There was an increasing trend in the total number of publications on movement disorders during the last two decades. Singapore had the highest contribution in all aspects, which highlights the impact of knowledge-based economy type in research productivity. Parkinsonism remained the most studied condition, followed by dystonia, chorea, and tremor. Among the socioeconomic factors, only % gross domestic product (GDP) for research and development showed a positive correlation on the number of publications of a country. On the other hand, GDP per capita, population size and the number of neurologist size did not affect research productivity.

CONCLUSIONS

An increasing trend in the movement disorders research output over the last 20 years was seen. Singapore had the highest contribution in all aspects which highlights the impact of economy in research productivity. Among the socioeconomic factors, only % GDP for R&D showed a positive impact on the number of publications of a country.

Psychiatric morbidity and poor follow-up underlie suboptimal functional and survival outcomes in Huntington's disease

Background

Huntington’s disease (HD), an inherited, often late-onset, neurodegenerative disorder, is considered to be a rare, orphan disease. Research into its genetic correlates and services for those affected are inadequate in most low-middle income countries, including India. The apparent ‘incurability’ often deters symptomatic and rehabilitative care, resulting in poor quality of life and sub-optimal outcomes. There are no studies assessing disease burden and outcomes from India.

Methods

We attempted to evaluate individuals diagnosed to have HD at our tertiary-care center between 2013 and 2016 for clinical symptoms, functionality, mortality, follow up status through a structured interview, clinical data from medical records and UHDRS-TFC scoring.

Results

Of the 144 patients, 25% were untraceable, and another 17 (11.8%) had already died. Mean age at death and duration of illness at the time of death, were 53 years and 7 years respectively, perhaps due to suicides and other comorbidities at an early age. The patients who could be contacted (n = 81) were assessed for morbidity and total functional capacity (TFC). Mean CAG repeat length and TFC score were 44.2 and 7.5 respectively. Most individuals (66%) were in TFC stage I and II and could perhaps benefit from several interventions. The TFC score correlated inversely with duration of illness (p < 0.0001). The majority were being taken care of at home, irrespective of the physical and mental disability. There was a high prevalence of psychiatric morbidity (91%) including suicidal tendency (22%). Three of the 17 who died had committed suicide, and several other families reported suicidal history in other family members. Only about half the patients (57%) maintained a regular clinical follow-up.

Conclusions

This study demonstrates the poor follow-up rates, significant suicidality and other psychiatric symptoms, sub-optimal survival durations and functional outcomes highlighting the need for holistic care for the majority who appear to be amenable to interventions.

A Review of the Clinical Evidence for Complementary and Alternative Medicine in Huntington's Disease

Background

There is a lack of published guidelines related to the use of complementary and alternative medicine (CAM) for Huntington’s disease (HD). We conducted a review of the literature to summarize the available evidence for various mind–body practices and nutraceuticals.

Methods

PubMed and Cochrane Library electronic databases were searched independently from inception to February 2019 by two independent raters. Studies were classified for the level of evidence (Class I, II, III, or IV) according to the American Academy of Neurology (AAN) classification scale.

Results

Randomized controlled trials in HD were reviewed for mind–body interventions (dance therapy, music therapy, and exercise), alternative systems (traditional Chinese medicine [TCM]), and nutraceuticals/diet (aminooxyacetic acid [AOAA], coenzyme q10, creatine, cannabinoids, alpha-tocopherol, eicosapentaenoic acid, idebenone, levocarnitine, and triheptanoin). Few studies met AAN Class I or II level of evidence for benefits, and these are highlighted.

Discussion

There is a relative paucity of clinical trials examining CAM modalities in HD when compared to other neurodegenerative disorders. Currently, there is no evidence supporting disease modification or symptom improvement with any specific dietary or nutraceutical supplement for HD. Supervised exercise and contemporary dance are safe for people with HD, but more robust studies are warranted to guide specific recommendations for these and other mind–body interventions.

Effect of Regulatory Network of Exosomes and microRNAs on Neurodegenerative Diseases

OBJECTIVE

A comprehensive review of the network regulation of exosomes and microRNAs (miRNAs) in neurodegenerative diseases was done, centering on the mechanism of the formation of exosomes and miRNAs and the sorting mechanism of exosomal miRNAs, with the aim to provide a theoretical basis in the search of biomarkers and the treatment of neurodegenerative diseases.

DATA SOURCES

The comprehensive search used online literature databases including NCBI PubMed, Web of Science, Google Scholar, and Baidu Scholar.

STUDY SELECTION

The study selection was based on the following keywords: exosomes, miRNAs, central nervous system (CNS), and neurodegenerative diseases. The time limit for literature retrieval was from the year 2000 to 2018, with language restriction in English. Relevant articles were carefully reviewed, with no exclusions applied to study design and publication type.

RESULTS

Exosomes are the smallest nanoscale membranous microvesicles secreted by cells and contain important miRNAs, among other rich contents. In the CNS, exosomes can transport amyloid β-protein, α-synuclein, Huntington-associated protein 1, and superoxide dismutase I to other cells. These events relieve the abnormal accumulation of proteins and aggravating neurological diseases. In some neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis, miRNAs are pathologically altered as an inexorable course, suggesting that miRNAs may contribute neurodegeneration. Exosomes and miRNAs form a network to regulate the homeostasis of the CNS, both synergistically and individually.

CONCLUSION

The network of exosomes and miRNAs that regulates CNS homeostasis is a promising biomarker for the diagnosis and treatment of neurodegenerative diseases.

The adjustment of γ-aminobutyric acidA tonic subunits in Huntington's disease: from transcription to translation to synaptic levels into the neostriatum

γ-Aminobutyric acid (GABA), plays a key role in all stages of life, also is considered the main inhibitory neurotransmitter. GABA activates two kind of membrane receptors known as GABA_A and GABA_B, the first one is responsible to render tonic inhibition by pentameric receptors containing α4−6, β3, δ, or ρ1−3 subunits, they are located at perisynaptic and/or in extrasynaptic regions. The biophysical properties of GABA_A tonic inhibition have been related with cellular protection against excitotoxic injury and cell death in presence of excessive excitation. On this basis, GABA_A tonic inhibition has been proposed as a potential target for therapeutic intervention of Huntington's disease. Huntington's disease is a neurodegenerative disorder caused by a genetic mutation of the huntingtin protein. For experimental studies of Huntington's disease mouse models have been developed, such as R6/1, R6/2, HdhQ92, HdhQ150, as well as YAC128. In all of them, some key experimental reports are focused on neostriatum. The neostriatum is considered as the most important connection between cerebral cortex and basal ganglia structures, its cytology display two pathways called direct and indirect constituted by medium sized spiny neurons expressing dopamine D1 and D2 receptors respectively, they display strong expression of many types of GABA_A receptors, including tonic subunits. The studies about of GABA_A tonic subunits and Huntington's disease into the neostriatum are rising in recent years, suggesting interesting changes in their expression and localization which can be used as a strategy to delay the cellular damage caused by the imbalance between excitation and inhibition, a hallmark of Huntington's disease.

Quantitative Gait Analysis in Patients with Huntington's Disease

Objective

Gait disturbance is the main factor contributing to a negative impact on quality of life in patients with Huntington’s disease (HD). Understanding gait features in patients with HD is essential for planning a successful gait strategy. The aim of this study was to investigate temporospatial gait parameters in patients with HD compared with healthy controls.

Methods

We investigated 7 patients with HD. Diagnosis was confirmed by genetic analysis, and patients were evaluated with the Unified Huntington’s Disease Rating Scale (UHDRS). Gait features were assessed with a gait analyzer. We compared the results of patients with HD to those of 7 age- and sex-matched normal controls.

Results

Step length and stride length were decreased and base of support was increased in the HD group compared to the control group. In addition, coefficients of variability for step and stride length were increased in the HD group. The HD group showed slower walking velocity, an increased stance/swing phase in the gait cycle and a decreased proportion of single support time compared to the control group. Cadence did not differ significantly between groups. Among the UHDRS subscores, total motor score and total behavior score were positively correlated with step length, and total behavior score was positively correlated with walking velocity in patients with HD.

Conclusion

Increased variability in step and stride length, slower walking velocity, increased stance phase, and decreased swing phase and single support time with preserved cadence suggest that HD gait patterns are slow, ataxic and ineffective. This study suggests that quantitative gait analysis is needed to assess gait problems in HD.

Epidemiological Study of Huntington's Disease in the Province of Ferrara, Italy

BACKGROUND

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by the abnormal expansion of CAG triplet repeat. We aimed to reappraise HD epidemiology in a northern Italian population, in relation to introduction of genetic testing.

METHODS

Through ICD-9M code 333.4 and medical fare exemption code RF0080, HD cases were identified from administrative health data and medical records from the Units of Neurology and Genetics, Ferrara University Hospital, and from other provincial neurological structures.

RESULTS

HD mean annual incidence rate in 1990-2009 was 0.3 per 100,000 (95% CI 0.2-0.5). All incident cases were found to have symptoms of the disease's classic form, and neither juvenile nor the rigid Westphal variant was detected. The mean (SD) age at onset was 50.2 (12.7 years; range 32-82 years), 54.9 (14.6) for men and 45.8 (9.4) for women. On prevalence day, December 31, 2014, HD prevalence was 4.2 per 100,000 (95% CI 2.4-7.0), with a male:female ratio of 1:2.

CONCLUSIONS

The prevalence and incidence of HD in our population were lower than the prevalence and incidence reported for other European and Italian populations, but higher compared to those of Asia, Africa, and Eastern Europe. Compared to previous studies, HD incidence and prevalence did not change significantly.

Clinical and genetic investigation of a Brazilian family with Huntington's disease

The aim of this study was to investigate a Brazilian family carrying full penetrance alleles for Huntington's disease (HD) in order to correlate each member's genetic and clinical features. To this end, the following scales were administered in each patient: the Beck Depression Inventory, the Mini-Mental State Examination (MMSE) and the Unified Huntington's Disease Rating Scale (UHDRS). The patterns of CAG and CCG polymorphic regions in the HTT gene were determined, the disease burden score was calculated, and genotypes were correlated with phenotypes within this family. We suggest that HD duration, the number of years of formal education, and UHDRS status variables can explain 96.6% of the MMSE variability in HD patients. A strong significant correlation was found between the disease burden score and the UHDRS (r = 0.76; p-value = 0.049) and the MMSE (r = -0.90; p-value = 0.006). The correlations between CAG allele size and the three clinical evaluations performed in the HD patients were not statistically significant.

Chrysin exerts neuroprotective effects against 3-Nitropropionic acid induced behavioral despair-Mitochondrial dysfunction and striatal apoptosis via upregulating Bcl-2 gene and downregulating Bax-Bad genes in male wistar rats

3-Nitropropionic acid (3-NP) is an irreversible inhibitor of mitochondrial complex-II that causes transcriptional dysregulation, bioenergetics failure, protein aggregation and oxidative damage similar to Huntington's disease (HD) pathogenesis. Chrysin, a bioactive flavonoid reported to have anti-inflammation, antioxidant, vasorelaxant and neuroprotective property. The present study was framed to determine the neuroprotective efficiency of chrysin upon 3-NP induced oxidative stress, mitochondrial dysfunctions and neurodegeneration. 3-NP (10mg/kg b.w. i.p.) administration for 14days exhibited significant (P<0.01) behavioral alterations, mitochondrial dysfunction and oxidative damages to biomolecules, finally causes cell death. Chrysin at 50mg/kg b.w. orally for 14days improved all the behavioral performances and regulated the complex activities in mitochondria. Further, chrysin diminished the oxidative stress markers (lipid peroxidation, nitrite and protein carbonyls) by significantly (P<0.01) improving the antioxidant status (superoxide dismutase, catalase and reduced glutathione) in striatal mitochondria. Indeed, chrysin prevents apoptosis by upregulating the Bcl-2 mRNA expression and downregulating the pro-apoptotic (Bax, Bad) mRNAs in 3-NP induced condition. Furthermore, the survival of striatal neurons against 3-NP toxicity was enhanced upon chrysin treatment which was evidenced by observing histopathological studies. Hence, the present study collectively suggests that the chrysin can serve as a potential therapeutic agent on 3-NP induced mitochondrial deficits and subsequent apoptosis.

The global prevalence of Huntington's disease: a systematic review and discussion

The ascertained prevalence of Huntington's disease (HD) increased significantly following the provision of diagnostic testing. A systematic review was conducted to estimate the prevalence of HD in the post-diagnostic testing era. 22 studies with original data pertaining to the prevalence of HD (1993-2015) were included and analyzed. A global meta-analysis was not performed due to heterogeneity in study methods and geographical variation. The prevalence of HD is significantly lower in Asian populations compared with western Europe, North America and Australia. The global variation in HD prevalence is partly explained by the average CAG repeat lengths and frequency of different HTT gene haplotypes in the general population. Understanding the prevalence of HD has significant implications for healthcare resource planning.

Incidence of adult Huntington's disease in the UK: a UK-based primary care study and a systematic review

OBJECTIVES

The prevalence of Huntington's disease (HD) recorded in the UK primary care records has increased twofold between 1990 and 2010. This investigation was undertaken to assess whether this might be due to an increased incidence. We have also undertaken a systematic review of published estimates of the incidence of HD.

SETTING

Incident patients with a new diagnosis of HD were identified from the primary care records of the Clinical Practice Research Datalink (CPRD). The systematic review included all published estimates of the incidence of HD in defined populations.

PARTICIPANTS

A total of 393 incident cases of HD were identified from the CPRD database between 1990 and 2010 from a total population of 9,282,126 persons.

PRIMARY AND SECONDARY OUTCOME MEASURES

The incidence of HD per million person-years was estimated. From the systematic review, the extent of heterogeneity of published estimates of the incidence of HD was examined using the I(2) statistic.

RESULTS

The data showed that the incidence of HD has remained constant between 1990 and 2010 with an overall rate of 7.2 (95% CI 6.5 to 7.9) per million person-years. The systematic review identified 14 independent estimates of incidence with substantial heterogeneity and consistently lower rates reported in studies from East Asia compared with those from Australia, North America and some--though not all--those from Europe. Differences in incidence estimates did not appear to be explained solely by differences in case ascertainment or diagnostic methods.

CONCLUSIONS

The rise in the prevalence of diagnosed HD in the UK, between 1990 and 2010, cannot be attributed to an increase in incidence. Globally, estimates of the incidence of HD show evidence of substantial heterogeneity with consistently lower rates in East Asia and parts of Europe. Modifiers may play an important role in determining the vulnerability of different populations to expansions of the HD allele.