Genetic aspects of Huntington's disease in Latin America. A systematic review

Huntington's Disease in Chile: Epidemiological and Genetic Aspects

INTRODUCTION

Huntington's disease (HD) is a neurodegenerative, autosomal dominant disabling condition due to an expansion of the CAG trinucleotide in the HTT gene. Motor, psychiatric, and cognitive disorders characterize it. Chilean reports on HD in the era of molecular diagnosis were wanted.

METHODS

This is a retrospective analysis of a prospective cohort of patients with HD seen at the Center for Movement Disorders (CETRAM) in Chile between 2013 and 2019. Sociodemographic, genotype, and neuropsychiatric features were investigated.

RESULTS

One hundred three probands with HD were identified. The majority (63.1%) were born in the metropolitan region, followed by the VIII and V regions with 8.73% and 7.76%, respectively. When pedigrees were analyzed, ninety unrelated families encompassing 1,007 individuals were identified; among relatives, other 35 manifested HD, and 106 died of HD. Besides, five hundred seventy-nine individuals were at genetic risk. The minimum estimated prevalence of HD in Chile in 2019 was 0.72 × 100,000 inhabitants. The mean CAG repeats (CAGR) of 47.2 ± 10.74 for the expanded allele and 17.93 ± 2.05 for the normal allele. The mean age of onset was 41.39 ± 13.47 years. Juvenile cases represented 7.8% of this cohort, and 4.9% had a late onset. There was a negative correlation between the age of onset and the CAGR of the expanded allele (r =-0.84 p < 0.0001). Besides, 79.6% had a family history of HD.

CONCLUSIONS

This is the first report characterizing genetics, motor, and neuropsychiatric features in patients with HD in Chile. The mean length of CAGR expansion of the abnormal allele was similar to previous reports in North America (i.e., Mexico and Canada) and higher than that reported in the neighboring country of Argentina. According to previous estimations, the minimal prevalence of HD in Chile may be lower than expected.

Juvenile-Onset Huntington's Disease in Peru: A Case Series of 32 Patients

Background

Juvenile-onset Huntington's Disease (JoHD) or Huntington's disease (HD) with age of onset ≤20 years, is a rare clinical entity that often differs phenotypically from adult HD and represents only 1-15% of total HD cases.

Objective

To characterize the genetic and clinical characteristics of 32 JoHD patients seen in a Peruvian Neurogenetics clinic from 2000-2018.

Methods

This study is a retrospective clinical and genetic review. The clinical database in Lima, Peru was searched for HD patients seen in clinic between 2000 and 2018. Inclusion criteria were: (1) genetically confirmed disease; and (2) HD age of onset ≤20 years, according to the documented medical history.

Results

Among 475 patients with genetically confirmed HD in the database, 32 patients (6.7%) had symptom onset at ≤20 years. Among JoHD patients with a known transmitting parent (30 of 32), paternal transmission accounted for 77% of cases. Anticipation was higher with paternal transmission compared to maternal transmission (27.5 ± 11.5 vs. 11.3 ± 7.1 years). Overall expanded CAG repeat length ranged from 44 to 110, with a mean length of 65.6 ± 15.4, and 14 (44%) cases had repeat length under 60. Of the 32 patients included in the study, 25 had detailed clinical symptomatology available, and many patients had unique clinical features such as prominent sleep disturbance (60% of patients), or parkinsonism (73%).

Conclusions

This large case series of JoHD patients characterizes the Peruvian JoHD population, reports on unique familial relationships in JoHD, and highlights the varied symptomatic presentation of this rare disease.

Converging evidence in support of omega-3 polyunsaturated fatty acids as a potential therapy for Huntington's disease symptoms

Huntington's disease (HD) is a genetic, inexorably fatal neurodegenerative disease. Patient average survivability is up to 20 years after the onset of symptoms. Those who suffer from the disease manifest motor, cognitive, and psychiatric impairments. There is indirect evidence suggesting that omega-3 polyunsaturated fatty acids (ω-3 PUFA) could have alleviating effects on most of HD symptoms. These include beneficial effects against cachexia and weight loss, decrease of cognitive impairment over time, and improvement of psychiatric symptoms such as depression and irritability. Furthermore, there is a positive correlation between consumption of ω-3 PUFAs in diets and prevalence of HD, as well as direct effects on the disease via release of serotonin. Unfortunately, to date, very few studies have examined the effects of ω-3 PUFAs in HD, both on the symptoms and on disease progression. This paper reviews evidence in the literature suggesting that ω-3 PUFAs can be used in neurodegenerative disorders. This information can be extrapolated to support further research of ω-3 PUFAs and their potential use for HD treatment.

Huntington's disease among immigrant groups and Swedish-born individuals: a cohort study of all adults 18 years of age and older in Sweden

BACKGROUND

There is a lack of studies of Huntington's disease (HD) in immigrants.

OBJECTIVE

To study the association between country of birth and incident HD in first-generation immigrants versus Swedish-born individuals and in second-generation immigrants versus Swedish-born individuals with Swedish-born parents.

METHODS

Study populations included all adults aged 18 years and older in Sweden, i.e., in the first-generation study 6,042,891 individuals with 1034 HD cases and in the second-generation study 4,860,469 individuals with 1001 cases. HD was defined as having at least one registered diagnosis of HD in the National Patient Register. The incidence of HD in different first-generation immigrant groups versus Swedish-born individuals was assessed by Cox regression, expressed as hazard ratios (HRs) and 95% confidence intervals (CI). The models were stratified by sex and adjusted for age, geographical residence in Sweden, educational level, marital status, and neighborhood socioeconomic status.

RESULTS

Mean age-standardized incidence rates per 100,000 person-years were for all Swedish-born 0.82 and for all foreign born 0.53 and for all men 0.73 and for all women 0.81, with the highest incidence rates for the group 80-84 years of age. After adjusting for potential confounders, the HRs were lower in women in the first- and second-generation, i.e., 0.49 (95% CI 0.36-0.67) and 0.63 (95% 0.45-0.87), respectively, and also among women from Finland or with parents from Finland.

SIGNIFICANCE

In general, the risk of HD was lower in first-generation and second-generation immigrant women but not among male immigrants.

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.

DYNLT1 gene expression is downregulated in whole blood of patients at different Huntington's disease stages

Huntington's disease (HD) is a neurodegenerative disorder caused by a CAG nucleotide expansion, which encodes the amino acid glutamine, in the huntingtin gene. HD is characterized by motor, cognitive, and psychiatric dysfunctions. In a previous study, we showed by qPCR that some genes altered in an HD mouse model were also altered in blood of HD patients. These alterations were mainly with respect to the dynein family. Therefore, this study aimed to investigate whether dynein light chain Tctex type 1 (DYNLT1) is altered in HD patients and if there is a correlation between DYNLT1 gene expression changes and disease progression. We assessed the DYNLT1 gene expression in the blood of 19 HD patients and 20 healthy age-matched controls. Also, in 6 of these patients, we analyzed the DYNLT1 expression at two time points, 3 years apart. The DYNLT1 gene expression in the whole blood of HD patients was significantly downregulated and this difference was widened in later stages. These data suggest that DYNLT1 could emerge as a peripheral prognostic indicator in HD and, also, might be a target for potential intervention in the future.

Economic burden of Huntington's disease in Peru

Background

Huntington’s disease (HD) is a devastating and fatal neurodegenerative disorder that leads to progressive disability, and over time to total dependence. The economic impact of HD on patients living in developing countries like Peru is still unknown. This study aims to estimate the economic burden by estimating direct and indirect costs of Huntington’s disease in Peru, as well as the proportion of direct costs borne by patients and their families.

Methods

Disease-cost cross-sectional study where 97 participants and their primary caregivers were interviewed using a common questionnaire. Prevalence and human capital approaches were used to estimate direct and indirect costs, respectively.

Results

The average annual cost of HD reached USD 8120 per patient in 2015. Direct non-healthcare costs represented 78.3% of total cost, indirect costs 14.4% and direct healthcare costs the remaining 7.3%. The mean cost of HD increased with the degree of patient dependency: from USD 6572 for Barthel 4 & 5 (slight dependency and total independency, respectively) to USD 23,251 for Barthel 1 (total dependency). Direct costs were primarily financed by patients and their families.

Conclusions

The estimated annual cost of HD for Peruvian society reached USD 1.2 million in 2015. The cost impact of HD on patients and their families is very high, becoming catastrophic for most dependent patients, and thus making it essential to prioritize full coverage by the State.

Minimal prevalence of Huntington's disease in the South of Brazil and instability of the expanded CAG tract during intergenerational transmissions

Huntington’s disease (HD) is due to dominant expansions of the CAG repeat of the HTT gene. Meiotic instability of the (CAG)_n might impact the disorder frequency. We report on HD minimal prevalence in Rio Grande do Sul (RS) state, Brazil, and on intergenerational instability of the (CAG)_n in HD families. Symptomatic and at-risk subjects from 179 HD families were ascertained between 2013 and 2016. Clinical, molecular and family history data were obtained. Expanded (CAG)_n length differences between parent and child (delta-expanded-(CAG)_n) were calculated. Effect of parental age on the (CAG)_n instability upon transmission was inferred by correlating delta-expanded-(CAG)_n between siblings to their age differences. HD minimal prevalence in RS state was estimated as 1.85:100,000 inhabitants. Alleles with (CAG)_27-35 were found on 21/384 non-disease associated chromosomes (5.5%); among 253 expanded alleles, four (1.6%) were within reduced penetrance range with (CAG)_36-39. In 32 direct transmissions, mean instability was larger among paternal than maternal transmissions. In direct transmissions and in 51 sibling pairs, parental age at the time of child birth were not correlated with delta-expanded-(CAG)_n. Briefly, HD prevalence in RS state was lower than those reported for European populations. Expanded (CAG)_n transmissions were unstable and not associated to parental age.

Huntington's disease-like disorders in Latin America and the Caribbean

Diseases with a choreic phenotype can be due to a variety of genetic etiologies. As testing for Huntington's disease (HD) becomes more available in previously resource-limited regions, it is becoming apparent that there are patients in these areas with other rare genetic conditions which cause an HD-like phenotype. Documentation of the presence of these conditions is important in order to provide appropriate diagnostic and clinical care for these populations. Information for this article was gathered in two ways; the literature was surveyed for publications reporting a variety of genetic choreic disorders, and movement disorders specialists from countries in Latin America and the Caribbean were contacted regarding their experiences with chorea of genetic etiology. Here we discuss the availability of molecular diagnostics for HD and for other choreic disorders, along with a summary of the published reports of affected subjects, and authors' personal experiences from the regions. While rare, patients affected by non-HD genetic choreas are evidently present in Latin America and the Caribbean. HD-like 2 is particularly prevalent in countries where the population has African ancestry. The incidence of other conditions is likely determined by other variations in ethnic background and settlement patterns. As genetic resources and awareness of these disorders improve, more patients are likely to be identified, and have the potential to benefit from education, support, and ultimately molecular therapies.

Population-specific genetic modification of Huntington's disease in Venezuela

Modifiers of Mendelian disorders can provide insights into disease mechanisms and guide therapeutic strategies. A recent genome-wide association (GWA) study discovered genetic modifiers of Huntington's disease (HD) onset in Europeans. Here, we performed whole genome sequencing and GWA analysis of a Venezuelan HD cluster whose families were crucial for the original mapping of the HD gene defect. The Venezuelan HD subjects develop motor symptoms earlier than their European counterparts, implying the potential for population-specific modifiers. The main Venezuelan HD family inherits HTT haplotype hap.03, which differs subtly at the sequence level from European HD hap.03, suggesting a different ancestral origin but not explaining the earlier age at onset in these Venezuelans. GWA analysis of the Venezuelan HD cluster suggests both population-specific and population-shared genetic modifiers. Genome-wide significant signals at 7p21.2-21.1 and suggestive association signals at 4p14 and 17q21.2 are evident only in Venezuelan HD, but genome-wide significant association signals at the established European chromosome 15 modifier locus are improved when Venezuelan HD data are included in the meta-analysis. Venezuelan-specific association signals on chromosome 7 center on SOSTDC1, which encodes a bone morphogenetic protein antagonist. The corresponding SNPs are associated with reduced expression of SOSTDC1 in non-Venezuelan tissue samples, suggesting that interaction of reduced SOSTDC1 expression with a population-specific genetic or environmental factor may be responsible for modification of HD onset in Venezuela. Detection of population-specific modification in Venezuelan HD supports the value of distinct disease populations in revealing novel aspects of a disease and population-relevant therapeutic strategies.

The molecular epidemiology of Huntington disease is related to intermediate allele frequency and haplotype in the general population

Huntington disease (HD) is the most common monogenic neurodegenerative disorder in populations of European ancestry, but occurs at lower prevalence in populations of East Asian or black African descent. New mutations for HD result from CAG repeat expansions of intermediate alleles (IAs), usually of paternal origin. The differing prevalence of HD may be related to the rate of new mutations in a population, but no comparative estimates of IA frequency or the HD new mutation rate are available. In this study, we characterize IA frequency and the CAG repeat distribution in fifteen populations of diverse ethnic origin. We estimate the HD new mutation rate in a series of populations using molecular IA expansion rates. The frequency of IAs was highest in Hispanic Americans and Northern Europeans, and lowest in black Africans and East Asians. The prevalence of HD correlated with the frequency of IAs by population and with the proportion of IAs found on the HD-associated A1 haplotype. The HD new mutation rate was estimated to be highest in populations with the highest frequency of IAs. In European ancestry populations, one in 5,372 individuals from the general population and 7.1% of individuals with an expanded CAG repeat in the HD range are estimated to have a molecular new mutation. Our data suggest that the new mutation rate for HD varies substantially between populations, and that IA frequency and haplotype are closely linked to observed epidemiological differences in the prevalence of HD across major ancestry groups in different countries.

Action-semantic and syntactic deficits in subjects at risk for Huntington's disease

Frontostriatal networks play critical roles in grounding action semantics and syntactic skills. Indeed, their atrophy distinctively disrupts both domains, as observed in patients with Huntington's disease (HD) and Parkinson's disease, even during early disease stages. However, frontostriatal degeneration in these conditions may begin up to 15 years before the onset of clinical symptoms, opening avenues for pre-clinical detection via sensitive tasks. Such a mission is particularly critical in HD, given that patients' children have 50% chances of inheriting the disease. Against this background, we assessed whether deficits in the above-mentioned domains emerge in subjects at risk to develop HD. We administered tasks tapping action semantics, object semantics, and two forms of syntactic processing to 18 patients with HD, 19 asymptomatic first-degree relatives, and sociodemographically matched controls for each group. The patients evinced significant deficits in all tasks, but only those in the two target domains were independent of overall cognitive state. More crucially, relative to controls, the asymptomatic relatives were selectively impaired in action semantics and in the more complex syntactic task, with both patterns emerging irrespective of the subjects' overall cognitive state. Our findings highlight the relevance of these dysfunctions as potential prodromal biomarkers of HD. Moreover, they offer theoretical insights into the differential contributions of frontostriatal hubs to both domains while paving the way for innovations in diagnostic procedures.

The targetable A1 Huntington disease haplotype has distinct Amerindian and European origins in Latin America

Huntington disease (HD) is a dominant neurodegenerative disorder caused by a CAG repeat expansion in the Huntingtin (HTT) gene. HD occurs worldwide, but the causative mutation is found on different HTT haplotypes in distinct ethnic groups. In Latin America, HD is thought to have European origins, but indigenous Amerindian ancestry has not been investigated. Here, we report dense HTT haplotypes in 62 mestizo Peruvian HD families, 17 HD families from across Latin America, and 42 controls of defined Peruvian Amerindian ethnicity to determine the origin of HD in populations of admixed Amerindian and European descent. HD in Peru occurs most frequently on the A1 HTT haplotype (73%), as in Europe, but on an unexpected indigenous variant also found in Amerindian controls. This Amerindian A1 HTT haplotype predominates over the European A1 variant among geographically disparate Latin American controls and in HD families from across Latin America, supporting an indigenous origin of the HD mutation in mestizo American populations. We also show that a proportion of HD mutations in Peru occur on a C1 HTT haplotype of putative Amerindian origin (14%). The majority of HD mutations in Latin America may therefore occur on haplotypes of Amerindian ancestry rather than on haplotypes resulting from European admixture. Despite the distinct ethnic ancestry of Amerindian and European A1 HTT, alleles on the parent A1 HTT haplotype allow for development of identical antisense molecules to selectively silence the HD mutation in the greatest proportion of patients in both Latin American and European populations.