RESUMO
BACKGROUND: Huntington's disease (HD)(MIM:143100) is an severe autosomal dominant neurodegenerative disease caused by the dynamic expansion of CAG trinucleotides (> 35) in the HTT gene [Genomic Coordinates- (GRCh38):4:3,074,680-3,243,959]. OBJECTIVES: The aim of this systematic review was to investigate the reported associations between the frequencies of the A1 and A2 haplotypes in HD-affected and non-affected populations from different countries on different continents, in order to demonstrate the overall profile of these haplotypes worldwide, pointing towards the most frequent haplotypes that could be useful for HTT mutant-specific allele silencing in different populations. METHODS: Publications in MEDLINE (PubMed) and Embase from the last 10 years (PROSPERO CRD42018115282) were assessed. RESULTS: A total of 20 articles from 113 were selected for evaluation in their entirety, and eight were eligible for this study. CONCLUSION: Regardless of the size of the CAG tract, the articles included in this review demonstrate that populations with high HD prevalence present higher frequencies of the A1 or A2 haplotypes than populations exhibiting low HD prevalence, even when similar average CAG numbers are noted. Based on the presented articles, we suggest that the haplotypic profile is more closely related to the ancestral origin than to the size of the CAG tract. The identification of populations presenting a higher frequency of high-risk genotypes can contribute to more accurate genetic counseling, in addition to providing knowledge on HD epidemiology. According to the continued progress in the development of specific genetic silencing therapies by different research groups and pharmaceutical companies, such as haplotype targeting strategies for allele-specific HTT suppression, we conclude that the definition of haplotypes in phase with CAG expansions will contribute to the design of gene-silencing drugs specific for different populations worldwide.
Assuntos
Doença de Huntington , Doenças Neurodegenerativas , Alelos , Haplótipos , Humanos , Proteína Huntingtina/genética , Doença de Huntington/epidemiologia , Doença de Huntington/genéticaRESUMO
A doença de Huntington (DH) é uma desordem neurodegenerativa, que cursa com distúrbios motores, cognitivos e comportamentais que contribuem para o comprometimento da funcionalidade. Este estudo investigou o grau de funcionalidade e acometimento de indivíduos portadores da DH, com o Índice de Barthel Modificado (IBM) e por meio do Disease Burden Score (DBS). As variáveis analisadas de cada indivíduo foram: a idade atual, o gênero, a idade de início da doença e o número das repetições CAG (gene HTT). Seis indivíduos foram avaliados, três do sexo masculino 63,6 anos (±10,9) e três do sexo feminino 58,3 anos (±14,2) com o diagnóstico genético positivo para DH provenientes do município de Ervália/MG. O sexo feminino apresentou a idade de início menor comparado ao sexo masculino, com média de 38,3 anos (±8,9) e 46,6 anos (±7,6), respectivamente. O valor médio do número de repetições CAG no sexo feminino foi de 46,3 (±4,1) e no sexo masculino, 42,33 (±1,5). O grau de desempenho funcional determinado pelo IBM foi de 9,3 (±1,1) para o sexo feminino, com dependência total, e para o sexo masculino, 36 (±4,3), com dependência severa. O valor médio obtido pelo DBS no sexo feminino foi de 596,8 (±101,9), com maior grau de acometimento da doença comparado ao sexo masculino com 425,1 (±39,2). O grupo de mulheres com DH apresentou início dos sintomas mais cedo com maior número de expansões CAG quando comparado ao grupo masculino. Todos os pacientes apresentaram dependência total em relação à execução das atividades de vida diária. Sugere-se que pesquisas futuras sejam realizadas com maior número de indivíduos afetados pela DH para que os resultados observados sejam confirmados.
Huntington's disease (HD) is a neurodegenerative disorder, presenting with motor, cognitive and behavioral impairments that contribute to the decrease of the functional performance. This study investigated the degree of functionality and impairment of individuals with HD using the Modified Barthel Index (MBI) and the Disease Burden Score (DBS). The following variables were investigated : the age of onset, the gender, the current age and the number of CAG (HTT gene) repeats. Six HD patients from the municipality of Ervália-MG, three males 63.6 years old (±10.9) and three females 58.3 years old (±14.2), who had a positive genetic diagnosis for HD, were investigated. The female group had the lowest age of onset with an average of 38.3 years (±8.9), compared to the male group, with 46.6 years (±7.6). The mean of the number of CAG repeats in the female gender was 46.3 (±4.1) and in the male, 42.33 (±1.5). The degree of functional performance assessed by IBM was 9.3 (±1.1) for the female group, with total dependence, and for the male group, 36 (±4.3), with severe dependence. The mean of DBS value in the female group was 596.8 (±101.9) with a higher degree of disease involvement compared to the male group 425.1 (±39.2). The group of women with HD showed earlier onset of symptoms with a greater number of CAG repeats when compared to the male group. All patients presented total dependence on daily living activities. We strongly suggest further research involving a larger group of individuals affected by HD for statistical validation.