Huntington disease: DNA analysis in Brazilian population

The Huntington's Disease Gene in an Italian Cohort of Patients with Bipolar Disorder

BACKGROUND AND OBJECTIVES

Huntington's disease (HD) is characterized by motor, cognitive and psychiatric manifestations and caused by an expansion of CAG repeats over 35 triplets on the huntingtin (HTT) gene. However, expansions in the range 27-35 repeats (intermediate allele) can be associated with pathological phenotypes. The onset of HD is conventionally defined by the onset of motor symptoms, but psychiatric disturbances can precede the motor phase by up to twenty years. The aims of the present study are to identify HD patients in the pre-motor phase of the disease among patients diagnosed with bipolar disorders and evaluate any differences between bipolar patients carrying the normal HTT allele and patients with the expanded HTT gene.

METHODS

We assessed the HTT genotype in an Italian cohort of 69 patients who were affected by either type 1 or type 2 bipolar disorder.

RESULTS

No patient was found to be a carrier of the pathological HTT allele, but 10% of bipolar subjects carried an intermediate allele. Carriers of the intermediate allele were older at the onset of psychiatric symptoms than non-carriers.

CONCLUSION

The pathological HTT gene was not associated with bipolar disorder, while we found a higher frequency of the intermediate allele among the bipolar population with respect to healthy controls. The identification of this subset of bipolar subjects has implications for the clinical management of patients and their family members and promotes further investigation into possible pathological mechanisms common to both HD and bipolar disorder.

CAG Repeat Instability in the Peripheral and Central Nervous System of Transgenic Huntington’s Disease Monkeys

Huntington’s Disease (HD) is an autosomal dominant disease that results in severe neurodegeneration with no cure. HD is caused by the expanded CAG trinucleotide repeat (TNR) on the Huntingtin gene (HTT). Although the somatic and germline expansion of the CAG repeats has been well-documented, the underlying mechanisms had not been fully delineated. Increased CAG repeat length is associated with a more severe phenotype, greater TNR instability, and earlier age of onset. The direct relationship between CAG repeat length and molecular pathogenesis makes TNR instability a useful measure of symptom severity and tissue susceptibility. Thus, we examined the tissue-specific TNR instability of transgenic nonhuman primate models of Huntington’s disease. Our data show a similar profile of CAG repeat expansion in both rHD1 and rHD7, where high instability was observed in testis, liver, caudate, and putamen. CAG repeat expansion was observed in all tissue samples, and tissue- and CAG repeat size-dependent expansion was observed. Correlation analysis of CAG repeat expansion and the gene expression profile of four genes in different tissues, clusterin (CLU), transferrin (TF), ribosomal protein lateral stalk subunit P1 (RPLP1), and ribosomal protein L13a (RPL13A), showed a strong correlation with CAG repeat instability. Overall, our data, along with previously published studies, can be used for studying the biology of CAG repeat instability and identifying new therapeutic targets.

Investigation of intermediate CAG alleles of the HTT in the general population of Rio de Janeiro, Brazil, in comparison with a sample of Huntington disease-affected families

BACKGROUND

Huntington disease (HD) (MIM: 143100) is a severe autosomal dominant neurodegenerative disease caused by the expansion of CAG trinucleotides (>35) in the HTT.

OBJECTIVE

To investigate the frequency of intermediate CAG alleles (IAs) in individuals residing in Rio de Janeiro city with no familial history of HD (general population, GP) in comparison with a sample of individuals from families presenting with HD who were previously investigated by our group (affected sample, AS).

RESULTS

The frequency of normal CAG alleles was 96.2%, while that of IAs was 3.6%, and that of reduced penetrance alleles was 0.2% in the GP (n = 470 chromosomes); 7.2% (17/235 individuals) of the GP presented an IA in heterozygosis with a normal allele. There was no statistically significant difference between the frequencies of the IAs in the GP and in the AS (p = .9). The most frequent haplotype per normal allele was (CAG)17-(CCG)7 (101/461) and per IA was (CAG)27-(CCG)7 (6/17) in the GP. These haplotypes were also the most frequent in the normal and IA chromosomes of the AS, respectively.

CONCLUSION

The genetic profiles of the IAs obtained from GP and AS were rather similar. It is important to investigate the frequencies of the IAs because expansions arise from a step-by-step mechanism in which, during intergenerational transmission, large normal alleles can generate IAs, which are then responsible for generating de novo HD mutations. The genetic investigation of IAs in the GP was also important because it was focused on the population of Rio de Janeiro, an understudied group. CCG7 was the most frequent CCG allele in linkage disequilibrium with normal, intermediate, and expanded CAG alleles, similar to the Western Europe population. However, a more robust investigation, in conjunction with haplogroup determination (A, B, or C), will be required to elucidate the ancestral origin of the HTT mutations in Brazilians.

A Study of Triplet-Primed PCR for Identification of CAG Repeat Expansion in the HTT Gene in a Cohort of 503 Indian Cases with Huntington's Disease Symptoms

BACKGROUND

Huntington's disease (HD) is an autosomal-dominant neurodegenerative disorder with an average age at onset of 40 years. It is a polyglutamine (polyQ) disorder that is caused by an increase in the number of CAG repeats in the huntingtin (HTT) gene. Genetic tests that accurately determine the number of CAG repeats are performed for confirmation of diagnosis, predictive testing of persons at genetic risk for inheriting HD, and prenatal testing. The aim of our study was to evaluate efficacy of triplet-primed polymerase chain reaction (TP-PCR) for routine diagnosis of HD in suspected cases from India.

METHODS

We evaluated a combination of CAG flanking PCR and triplet-primed PCR for estimation of CAG repeats in 503 cases with clinical suspicion of HD.

RESULTS

There were 250 cases (49.7%) that showed the presence of expanded alleles, with 241 (47.9%) being fully penetrant alleles and nine (1.8%) in the reduced penetrance category. There were seven juvenile cases with an age of onset of < 20 years, with the longest allele comprising 106 CAG repeats found in an 8-year-old male patient. The results demonstrated an inverse (R = - 0.67) relationship between CAG length and age at clinical onset.

CONCLUSION

Our study on pan-Indian cases is one of the largest studies reported so far in India and focuses on the most accurate and comprehensive molecular diagnostic evaluation of HD.

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.

Study of the Huntington's disease IT-15 gene in different ethnic groups in Ecuador

This study aims to establish the current state of the IT-15 (HTT) gene in different Ecuadorian ethnic groups and patients by determining CAG triplet repeats, compared with the ethnicity of individuals. A total of 412 individuals were studied using nested polymerase chain reaction and Sanger sequencing: 75 individuals were indigenous (Kichwas), 211 mestizos, and 65 Afro-Ecuadorians. We included 31 patients who were clinically diagnosed with Huntington's disease (HD) and relatives of the affected patients (n = 30). Moreover, we correlated the presence of HD in Ecuadorian patients with 46 genetic ancestry-informative insertion-deletion polymorphic markers. We found that 77.20% had <28 CAG repetitions, 18.80% had mutable alleles, 2.27% had incomplete penetrance, and 1.70% reflected >39 repetitions. The average of CAG repetitions was 24 ± 3 for indigenous people; 28 ± 2 for mestizos; and 24 ± 3.2 repetitions for the Afro-Ecuadorians. The ancestral component showed that the main ancestry corresponded to Native Americans (0.873) and European ascendants (0.145), Africans were less represented in the evaluated population (0.018). There was a significant difference between the number of CAG repeats in mestizos and indigenous people (P < .01), suggesting that the Ecuadorian mestizo population has a risk factor for the gene mutation.

Genetic counseling and testing for Huntington's disease: A historical review

This manuscript describes the ways in which genetic counseling has evolved since John Pearson and Sheldon Reed first promoted "a genetic education" in the 1950s as a voluntary, non-directive clinical tool for permitting individual decision making. It reviews how the emergence of Huntington's disease (HD) registries and patient support organizations, genetic testing, and the discovery of a disease-causing CAG repeat expansion changed the contours of genetic counseling for families with HD. It also reviews the guidelines, outcomes, ethical and laboratory challenges, and uptake of predictive, prenatal, and preimplantation testing, and it casts a vision for how clinicians can better make use of genetic counseling to reach a broader pool of families that may be affected by HD and to ensure that genetic counseling is associated with the best levels of care. © 2016 Wiley Periodicals, Inc.

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.

Genomic Instability Associated with p53 Knockdown in the Generation of Huntington's Disease Human Induced Pluripotent Stem Cells

Alterations in DNA damage response and repair have been observed in Huntington's disease (HD). We generated induced pluripotent stem cells (iPSC) from primary dermal fibroblasts of 5 patients with HD and 5 control subjects. A significant fraction of the HD iPSC lines had genomic abnormalities as assessed by karyotype analysis, while none of our control lines had detectable genomic abnormalities. We demonstrate a statistically significant increase in genomic instability in HD cells during reprogramming. We also report a significant association with repeat length and severity of this instability. Our karyotypically normal HD iPSCs also have elevated ATM-p53 signaling as shown by elevated levels of phosphorylated p53 and H2AX, indicating either elevated DNA damage or hypersensitive DNA damage signaling in HD iPSCs. Thus, increased DNA damage responses in the HD genotype is coincidental with the observed chromosomal aberrations. We conclude that the disease causing mutation in HD increases the propensity of chromosomal instability relative to control fibroblasts specifically during reprogramming to a pluripotent state by a commonly used episomal-based method that includes p53 knockdown.

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

We aimed to present a systematic review on Huntington's disease (HD) in Latin America (LA). PubMed and LILACS were searched up to March 2015, reporting confirmed HD cases in LA. Case series, cross-sectional, case-control, and prospective studies were included. From 534 communications, 47 were eligible. Population-based studies were not found; minimal prevalence of 0.5-4/100,000 was estimated for Venezuela and Mexico. Geographical isolates were well characterized in Venezuela and in Peru. CAG repeats at HTT gene varied between 7-33 and 37-112 in normal and expanded alleles, respectively. Intermediate alleles were found in 4-10% of controls. Ages at onset and the expanded CAG repeats correlated with r from - 0.55 to -0.91. While haplotype patterns of Venezuelan and Brazilian chromosomes were similar to those observed in Europeans, haplotypes from Peruvian HD patients did not match the same pattern. The limited number of papers found suggests that HD is poorly diagnosed in LA. Minimal prevalence seemed to be halfway between those of Caucasians and Asians. Range of CAG repeats was similar to those of Europeans. Haplotype studies indicate that majority of HD patients might be of Caucasian descent; an Asian origin for some Peruvian patients was proposed.

Examination of Huntington's disease in a Chinese family

We report brain imaging and genetic diagnosis in a family from Wuhan, China, with a history of Huntington's disease. Among 17 family members across three generations, four patients (II2, II6, III5, and III9) show typical Huntington's disease, involuntary dance-like movements. Magnetic resonance imaging found lateral ventricular atrophy in three members (II2, II6, and III5). Moreover, genetic analysis identified abnormally amplified CAG sequence repeats (> 40) in two members (III5 and III9). Among borderline cases, with clinical symptoms and brain imaging features of Huntington's disease, two cases were identified (II2 and II6), but shown by mutation analysis for CAG expansions in the important transcript 15 gene, to be non-Huntington's disease. Our findings suggest that clinical diagnosis of Huntington's disease requires a combination of clinical symptoms, radiological changes, and genetic diagnosis.

Haplotype analysis of the CAG and CCG repeats in 21 Brazilian families with Huntington's disease

We studied the allelic profile of CAG and CCG repeats in 61 Brazilian individuals in 21 independent families affected by Huntington's disease (HD). Thirteen individuals had two normal alleles for HD, two had one mutable normal allele and no HD phenotype, and forty-six patients carried at least one expanded CAG repeat allele. Forty-five of these individuals had one expanded allele and one individual had one mutable normal allele (27 CAG repeats) and one expanded allele (48 CAG repeats). Eleven of these forty-five subjects had a mutant allele with reduced penetrance, and thirty-four patients had a mutant allele with complete penetrance. Inter- and intragenerational investigations of CAG repeats were also performed. We found a negative correlation between the number of CAG repeats and the age of disease onset (r=-0.84; P<0.001) and no correlation between the number of CCG repeats and the age of disease onset (r=0.06). We found 40 different haplotypes and the analysis showed that (CCG)(10) was linked to a CAG normal allele in 19 haplotypes and to expanded alleles in two haplotypes. We found that (CCG)(7) was linked to expanded CAG repeats in 40 haplotypes (95.24%) and (CCG)(10) was linked to expanded CAG repeats in only two haplotypes (4.76%). Therefore, (CCG)(7) was the most common allele in HD chromosomes in this Brazilian sample. It was also observed that there was a significant association of (CCG)(7) with the expanded CAG alleles (χ(2)=6.97, P=0.0084). Worldwide, the most common CCG alleles have 7 or 10 repeats. In Western Europe, (CCG)(7) is the most frequent allele, similarly to our findings.

The Prevalence of Juvenile Huntington's Disease: A Review of the Literature and Meta-Analysis

Juvenile Huntington's disease (JHD) is usually defined as Huntington's disease with an onset ≤ 20 years. The proportion of JHD cases reported in studies of Huntington's disease (HD) varies. A review of the literature found 62 studies that reported the proportion of JHD cases amongst all HD cases. The proportion of JHD cases in these studies ranged from 1% to 15%, and in a meta-analysis the pooled proportion of JHD cases was 4.92% (95% confidence interval of 4.07% to 5.84%). Limiting the analysis to the 25 studies which used multiple methods of ascertainment resulted in a similar pooled proportion of 5.32%, (95% confidence interval 4.18% to 6.60%). A small difference was observed when the meta-analysis was restricted to studies from countries defined by the World Bank as high income, that used multiple methods of ascertainment, and that were conducted since 1980 (4.81%, 95% confidence interval 3.31% to 6.58%, n=11). This contrasts with the pooled result from three post 1980 studies using multiple methods of ascertainment from South Africa and Venezuela, defined by the World Bank as upper middle income, where the estimated mean proportion was 9.95%, (95% confidence interval 6.37% to 14.22%). These results, which are expected to be more robust than those from a single study alone, may be helpful in estimating the proportion of JHD cases in a given population. Key Words: Juvenile Huntington's disease, prevalence, epidemiology.

Non-choreic movement disorders as initial manifestations of Huntington's disease

We describe seven patients with genetically confirmed Huntington's disease (HD) who had non-choreic movement disorders as presenting symptoms or signs. Patients with movement disorders other than chorea in the early stages tended to have larger CAG trinucleotide repeat expansion in comparison with more "typical" HD patients.

Huntington disease mutation in Venezuela: age of onset, haplotype analyses and geographic aggregation

The aggregation of patients with Huntington's disease (HD) around Lake Maracaibo, Zulia State, Venezuela, is widely recognized, but the epidemiology of HD in the whole country is relatively unstudied. We have examined 279 individuals from 60 unrelated affected families residing in various areas of Venezuela for the presence of CAG repeats and other features associated with HD. The number of expanded repeats in 139 carriers varied from 35 to 112. Based on our examination of 71 symptomatic individuals, we developed a log-transformed regression equation, y= -0.0238x + 2.6616, to enable the prediction of age of onset in asymptomatic carriers. Intragenic haplotypes were constructed with two VNTRs (variable number of tandem repeats) and two SNPs (single nucleotide polymorphisms) in the promoter region as well as CCG repeat and Delta2642 polymorphisms to assess kinship between families. In 43 of 45 tested families, the haplotype on the mutated chromosome was 1;G;C;7;(A). The other haplotypes observed, 1;G;C;7;(B) and 4;G;C;7;(A), were of Peruvian and French origins, respectively. The geographic source of the first affected ancestor was assessed in 54 families from 15 different states. Residents of the states of Miranda, Lara and Táchira, excluding those of Zulia, had a mutated allele prevalence five- to ninefold higher than that of other areas. A low (approx. 1/200,000) prevalence, a wide-spread distribution with aggregation in some states and a likely remote European Caucasoid origin are defining epidemiologic features of HD in Venezuela.

Internal consistency of a Brazilian version of the unified Huntington's disease rating scale

We evaluated the reliability of a translated Brazilian version of the Unified Huntington's Disease Rating Scale (UHDRS) to establish the reproducibility of the scale in a population that differs substantially from that on which the scale was originally validated. After a training period with the video and guidelines requested from the Huntington Study Group, we applied the UHDRS, except for the cognitive tests, to a group of 21 Brazilian patients with a molecular diagnosis of Huntington's disease (HD). We found a high degree of internal consistency of the motor section of the UHDRS (Cronbach's alpha= 0.841). There was a negative correlation between the total motor score and the functional assessment, the independence scale and the functional capacity. There was a positive correlation between these 3 scales of functional evaluation and a negative correlation between the age of onset of the disease and the number of CAG repeats. The behavioral scale and disease duration were not correlated with any factor. The clinical characteristics of this sample of patients as described by the UHDRS were roughly similar to those reported in the original validation studies and the correlations described were similar to those reported previously. We conclude that the Brazilian version of the UHDRS is reliable and valid to study patients with HD in the Brazilian setting, that this sample of Brazilian patients had clinical characteristics similar to those observed in other world regions, as expected, and that the clinical training method used for the application of the UHDRS was effective to insure a high degree of clinical reproducibility.