EMQN/CMGS best practice guidelines for the molecular genetic testing of Huntington disease

The First Case of Huntington's Disease like 2 in Mali, West Africa

Background

Huntington's disease like 2 (HDL2) has been reported exclusively in patients with African ancestry, mostly originating from South Africa.

Case report

We report three patients in Mali including a proband and his two children who have been examined by neurologists and psychiatrists after giving consent. They were aged between 28 and 56 years old. Psychiatric symptoms were predominant in the two younger patients while the father presented mainly with motor symptoms. Genetic testing identified a heterozygous 40 CTG repeat expansion in the Junctophilin-3 (JPH3) gene in all three patients.

Discussion

This study supports the hypothesis that HDL2 may be widely spread across Africa.

Highlights

We report here the first case of HDL2 in West Africa, suggesting that HDL2 is widely spread across African continent, and increasing access to genetic testing could uncover other cases.

Attenuated huntingtin gene CAG nucleotide repeat size in individuals with Lynch syndrome

DNA mismatch repair (MMR) is thought to contribute to the onset and progression of Huntington disease (HD) by promoting somatic expansion of the pathogenic CAG nucleotide repeat in the huntingtin gene (HTT). Here we have studied constitutional HTT CAG repeat size in two cohorts of individuals with Lynch syndrome (LS) carrying heterozygous loss-of-function variants in the MMR genes MLH1 (n = 12/60; Lund cohort/Bochum cohort, respectively), MSH2 (n = 15/88), MSH6 (n = 21/23), and controls (n = 19/559). The sum of CAG repeats for both HTT alleles in each individual was calculated due to unknown segregation with the LS allele. In the larger Bochum cohort, the sum of CAG repeats was lower in the MLH1 subgroup compared to controls (MLH1 35.40 CAG repeats ± 3.6 vs. controls 36.89 CAG repeats ± 4.5; p = 0.014). All LS genetic subgroups in the Bochum cohort displayed lower frequencies of unstable HTT intermediate alleles and lower HTT somatic CAG repeat expansion index values compared to controls. Collectively, our results indicate that MMR gene haploinsufficiency could have a restraining impact on constitutional HTT CAG repeat size and support the notion that the MMR pathway is a driver of nucleotide repeat expansion diseases.

Diagnostic outcome of pro bono neurogenetic diagnostic service in Sri Lanka: A wealth creation

The inherited disease community in Sri Lanka has been widely neglected. This article aimed to present accumulated knowledge in establishing a pro bono cost-effective national, island-wide, free-of-charge molecular diagnostic service, suggesting a model for other developing countries. The project provided 637 molecular diagnostic tests and reports free of charge to a nation with limited resources. We pioneered the implementation of mobile clinics and home visits, where the research team acted as barefoot doctors with the concept of the doctor and the researcher at the patient's doorstep. Establishing pro bono, cost-effective molecular diagnostics is feasible in developing countries with limited resources and state funding through the effort of dedicated postgraduate students. This service could provide an accurate molecular diagnosis of Duchenne muscular dystrophy, Huntington's disease, Spinocerebellar ataxia, and Spinal muscular atrophy, a diagnostic yield of 54% (343/637), of which 43% (147/343) of the patients identified as amenable for available gene therapies. Initiated human resource development by double doctoral degree opportunities with international collaborations. Established a neurobiobank and a national registry in Sri Lanka, a rich and unique repository, wealth creation for translational collaborative research and sharing of information in neurological diseases, as well as a lodestar for aspiring initiatives from other developing countries.

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.

Genetic Testing in Clinical Movement Disorders: A Case-Based Review

Genetics are fundamental to understanding the pathophysiology of neurological disease, including movement disorders. Genetic testing in clinical practice has changed dramatically over the last few decades. While the likelihood of establishing an etiological diagnosis is greater now with increased access to testing and more advanced technologies, clinicians face challenges when deciding whether to test, then selecting the appropriate test, and ultimately interpreting and sharing the results with patients and families. In this review, we use a case-based approach to cover core aspects of genetic testing for the neurologist, namely, genetic testing in Parkinson's disease, interpretation of inconclusive genetic test reports, and genetic testing for repeat expansion disorders using Huntington disease as a prototype.

Gene therapy for selected neuromuscular and trinucleotide repeat disorders - An insight to subsume South Asia for multicenter clinical trials

Background

In this article, the authors discuss how they utilized the genetic mutation data in Sri Lankan Duchenne muscular dystrophy (DMD), Spinal muscular atrophy (SMA), Spinocerebellar ataxia (SCA) and Huntington's disease (HD) patients and compare the available literature from South Asian countries to identifying potential candidates for available gene therapy for DMD, SMA, SCA and HD patients.

Methods

Rare disease patients (n = 623) with the characteristic clinical findings suspected of HD, SCA, SMA and Muscular Dystrophy were genetically confirmed using Multiplex Ligation Dependent Probe Amplification (MLPA), and single plex PCR. A survey was conducted in the "Wiley database on Gene Therapy Trials Worldwide" to identify DMD, SMA, SCA, and HD gene therapy clinical trials performed worldwide up to April 2021. In order to identify candidates for gene therapy in other neighboring countries we compared our findings with available literature from India and Pakistan which has utilized the same molecular diagnostic protocol to our study.

Results

From the overall cohort of 623 rare disease patients with the characteristic clinical findings suspected of HD, SCA, SMA and Muscular Dystrophy, n = 343 (55%) [Muscular Dystrophy- 65%; (DMD-139, Becker Muscular Dystrophy -BMD-11), SCA type 1-3-53% (SCA1-61,SCA2- 23, SCA3- 39), HD- 52% (45) and SMA- 34% (22)] patients were positive for molecular diagnostics by MLPA and single plex PCR. A total of 147 patients in Sri Lanka amenable to available gene therapy; [DMD-83, SMA-15 and HD-49] were identified. A comparison of Sri Lankan finding with available literature from India and Pakistan identified a total of 1257 patients [DMD-1076, SMA- 57, and HD-124] from these three South Asian Countries as amenable for existing gene therapy trials. DMD, SMA, and HD gene therapy clinical trials (113 studies) performed worldwide up to April 2021 were concentrated mostly (99%) in High Income Countries (HIC) and Upper Middle-Income Countries (UMIC). However, studies on the potential use of anti-sense oligonucleotides (ASO) for treatment of SCAs have yet to reach clinical trials.

Conclusion

Most genetic therapies for neurodegenerative and neuromuscular disorders have been evaluated for efficacy primarily in Western populations. No multicenter gene therapy clinical trial sites for DMD, SMA and HD in the South Asian region, leading to lack of knowledge on the safety and efficacy of such personalized therapies in other populations, including South Asians. By fostering collaboration between researchers, clinicians, patient advocacy groups, government and industry in gene therapy initiatives for the inherited-diseases community in the developing world would link the Global North and Global South and breathe life into the motto "Together we can make a difference".

Cognitive Dysfunction in Repeat Expansion Diseases: A Review

With the development of the sequencing technique, more than 40 repeat expansion diseases (REDs) have been identified during the past two decades. Moreover, the clinical features of these diseases show some commonality, and the nervous system, especially the cognitive function was affected in part by these diseases. However, the specific cognitive domains impaired in different diseases were inconsistent. Here, we survey literature on the cognitive consequences of the following disorders presenting cognitive dysfunction and summarizing the pathogenic genes, epidemiology, and different domains affected by these diseases. We found that the cognitive domains affected in neuronal intranuclear inclusion disease (NIID) were widespread including the executive function, memory, information processing speed, attention, visuospatial function, and language. Patients with C9ORF72-frontotemporal dementia (FTD) showed impairment in executive function, memory, language, and visuospatial function. While in Huntington's disease (HD), the executive function, memory, and information processing speed were affected, in the fragile X-associated tremor/ataxia syndrome (FXTAS), executive function, memory, information processing speed, and attention were impaired. Moreover, the spinocerebellar ataxias showed broad damage in almost all the cognitive domains except for the relatively intact language ability. Some other diseases with relatively rare clinical data also indicated cognitive dysfunction, such as myotonic dystrophy type 1 (DM1), progressive myoclonus epilepsy (PME), Friedreich ataxia (FRDA), Huntington disease like-2 (HDL2), and cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS). We drew a cognitive function landscape of the related REDs that might provide an aspect for differential diagnosis through cognitive domains and effective non-specific interventions for these diseases.

Uncovering Essential Tremor Genetics: The Promise of Long-Read Sequencing

Long-read sequencing (LRS) technologies have been recently introduced to overcome intrinsic limitations of widely-used next-generation sequencing (NGS) technologies, namely the sequencing limited to short-read fragments (150–300 base pairs). Since its introduction, LRS has permitted many successes in unraveling hidden mutational mechanisms. One area in clinical neurology in need of rethinking as it applies to genetic mechanisms is essential tremor (ET). This disorder, among the most common in neurology, is a syndrome often exhibiting an autosomal dominant pattern of inheritance whose large phenotypic spectrum suggest a multitude of genetic etiologies. Exome sequencing has revealed the genetic etiology only in rare ET families (FUS, SORT1, SCN4A, NOS3, KCNS2, HAPLN4/BRAL2, and USP46). We hypothesize that a reason for this shortcoming may be non-classical genetic mechanism(s) underpinning ET, among them trinucleotide, tetranucleotide, or pentanucleotide repeat disorders. In support of this hypothesis, trinucleotide (e.g., GGC repeats in NOTCH2NLC) and pentanucleotide repeat disorders (e.g., ATTTC repeats in STARD7) have been revealed as pathogenic in patients with a past history of what has come to be referred to as “ET plus,” bilateral hand tremor associated with epilepsy and/or leukoencephalopathy. A systematic review of LRS in neurodegenerative disorders showed that 10 of the 22 (45%) genetic etiologies ascertained by LRS include tremor in their phenotypic spectrum, suggesting that future clinical applications of LRS for tremor disorders may uncover genetic subtypes of familial ET that have eluded NGS, particularly those with associated leukoencephalopathy or family history of epilepsy. LRS provides a pathway for potentially uncovering novel genes and genetic mechanisms, helping narrow the large proportion of “idiopathic” ET.

Deciphering Neurodegenerative Diseases Using Long-Read Sequencing

Neurodegenerative diseases exhibit chronic progressive lesions in the central and peripheral nervous systems with unclear causes. The search for pathogenic mutations in human neurodegenerative diseases has benefited from massively parallel short-read sequencers. However, genomic regions, including repetitive elements, especially with high/low GC content, are far beyond the capability of conventional approaches. Recently, long-read single-molecule DNA sequencing technologies have emerged and enabled researchers to study genomes, transcriptomes, and metagenomes at unprecedented resolutions. The identification of novel mutations in unresolved neurodegenerative disorders, the characterization of causative repeat expansions, and the direct detection of epigenetic modifications on naive DNA by virtue of long-read sequencers will further expand our understanding of neurodegenerative diseases. In this article, we review and compare 2 prevailing long-read sequencing technologies, Pacific Biosciences and Oxford Nanopore Technologies, and discuss their applications in neurodegenerative diseases.

On the hunt for a cure: A guide to Huntington disease

ABSTRACT

Huntington disease is a rare genetic disorder characterized by motor, cognitive, and psychiatric impairments. Although the typical patient has a positive family history and initially presents with chorea between ages 30 and 50 years, some patients do not have a typical presentation. Healthcare providers should know when to refer patients to neurology for testing for Huntington disease. The earlier the diagnosis is made, the earlier the patient and patient's family can receive education about the expected disease trajectory. A multidisciplinary approach is required to mitigate symptoms as the disease progresses. Although no cure exists, ongoing research is targeting genotypic abnormalities in hopes of finding a permanent treatment for Huntington disease.

False-negative tests in Huntington's disease: A new variant within primer hybridization site

BACKGROUND

Establishing the diagnosis of Huntington's disease (HD) involves molecular genetic testing and estimation of the number of CAG repeats.

MATERIAL AND METHODS

We report a 42-year-old patient with clinical phenotype suggestive of HD, who was repeatedly negative on genetic testing for HD at a reference laboratory. He had positive history of similar symptoms in his father, but not in other family members. During a 2-year follow-up his symptoms slowly deteriorated (videos attached). The family history was misleading, as we discovered that patient's father was adopted as infant. Having excluded HD-like disorders and other causes of the symptoms we hypothesized that the primer could not bind to the mutated allele.

RESULTS

The PCR reaction with primers HD1 and Hu3 revealed homozygosity of the other adjacent microsatellite tract consisting of the CCG repeats. The newly designed set of primers, located outside of the CAG tract (HD6extF, HD7extR) was used and enabled amplification of the mutant allele and detection of the abnormal range of CAG repeats.

CONCLUSIONS

As application of the novel primers led to the diagnosis of HD in other 5 patients previously tested negative, we propose their incorporation into routine genetic testing in patients suspected of HD displaying homoallelism in the standard protocol.

A Novel Triplet-Primed PCR Assay to Detect the Full Range of Trinucleotide CAG Repeats in the Huntingtin Gene (HTT)

The expanded CAG repeat number in HTT gene causes Huntington disease (HD), which is a severe, dominant neurodegenerative illness. The accurate determination of the expanded allele size is crucial to confirm the genetic status in symptomatic and presymptomatic at-risk subjects and avoid genetic polymorphism-related false-negative diagnoses. Precise CAG repeat number determination is critical to discriminate the cutoff between unexpanded and intermediate mutable alleles (IAs, 27–35 CAG) as well as between IAs and pathological, low-penetrance alleles (i.e., 36–39 CAG repeats), and it is also critical to detect large repeat expansions causing pediatric HD variants. We analyzed the HTT-CAG repeat number of 14 DNA reference materials and of a DNA collection of 43 additional samples carrying unexpanded, IAs, low and complete penetrance alleles, including large (>60 repeats) and very large (>100 repeats) expansions using a novel triplet-primed PCR-based assay, the AmplideX PCR/CE HTT Kit. The results demonstrate that the method accurately genotypes both normal and expanded HTT-CAG repeat numbers and reveals previously undisclosed and very large CAG expansions >200 repeats. We also show that this technique can improve genetic test reliability and accuracy by detecting CAG expansions in samples with sequence variations within or adjacent to the repeat tract that cause allele drop-outs or inaccuracies using other PCR methods.

Late-onset Huntington disease: An Italian cohort

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by a CAG expansion greater than 35 triplets in the IT-15 gene, with a clinical onset usually in the forties. Late-onset form of HD is defined as disease onset after the age of 59 years. The aim of the present study is to investigate the clinical-demographic features of Late-onset HD population (LoHD) in comparison to Classic-onset patients (CoHD). We analyzed a well-characterized Italian cohort of 127 HD patients, identifying 25.2% of LoHD cases. The mean age of onset was 65.9 and the mean length of pathological allele was 42.2. The 53.1% of LoHD patients had no family history of HD. No significant differences were observed in terms of gender, type of symptoms at disease onset, and clinical performance during the follow-up visits. The non-pathological allele resulted longer among LoHD patients. There is evidence that longer non-pathological allele is associated with a higher volume of basal ganglia, suggesting a possible protective role even in the onset of HD. In conclusion, LoHD patients in this Italian cohort were frequent, representing a quarter of total cases, and showed clinical features comparable to CoHD subjects. Due to the small sample size, further studies are needed to evaluate the influence of non-pathological alleles on disease onset.

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.

Risk Assessment for Huntington's Disease for (Future) Offspring Requires Offering Preconceptional CAG Analysis to Both Partners

Amongst the main reasons people at risk for Huntington's disease (HD) have for undergoing predictive genetic testing are planning a family and prevention of passing on an expanded CAG-repeat to future offspring. After having received an unfavourable test result, a couple may consider prenatal testing in the foetus or preimplantation genetic diagnostic testing (PGD) in embryos. Testing of the foetus or embryos is possible by means of direct testing of the expanded repeat. Optimal reliability in testing the foetus or embryos requires the establishment of the origin of the repeats of both parents in the foetus. For PGD the analysis is combined with or sometimes solely based on identification of the at-risk haplotype in the embryo. This policy implies that in the context of direct testing, the healthy partner's CAG repeat lengths in the HD gene are also tested, but with the expectation that the repeat lengths of the partner are within the normal range, with the proviso that the partner's pedigree is free of clinically confirmed HD. However, recent studies have shown that the expanded repeat has been observed more often in the general population than previously estimated. Moreover, we have unexpectedly observed an expanded repeat in the non-HD partner in four cases which had far-reaching consequences. Hence, we propose that in the context of reproductive genetic counselling, prior to a planned pregnancy, and irrespective of the outcome of the predictive test in the HD-partner, the non-HD partner should also be given the option of being tested on the expanded allele. International recommendations for predictive testing for HD should be adjusted.

Parental repeat length instability in myotonic dystrophy type 1 pre- and protomutations

Myotonic dystrophy type 1 (DM1) is caused by a CTG trinucleotide repeat expansion on chromosome 19q13.3. While DM1 premutation (36-50 repeats) and protomutation (51-80 repeats) allele carriers are mostly asymptomatic, offspring is at risk of inheriting expanded, symptom-associated, (CTG)n repeats of n > 80. In this study we aimed to evaluate the intergenerational instability of DM1 pre- and protomutation alleles, focussing on the influence of parental gender. One hundred and forty-six parent-child pairs (34 parental premutations, 112 protomutations) were retrospectively selected from the DM1 patient cohort of the Maastricht University Medical Center+. CTG repeat size of parents and children was determined by (triplet-primed) PCR followed by fragment length analysis and Southern blot analysis. Fifty-eight out of eighty-one (71.6%) paternal transmissions led to a (CTG)n repeat of n > 80 in offspring, compared with 15 out of 65 (23.1%) maternal transmissions (p < 0.001). Repeat length instability occurred for paternal (CTG)n repeats of n ≥ 45, while maternal instability did not occur until (CTG)n repeats reached a length of n ≥ 71. Transmission of premutations caused (CTG)n repeats of n > 80 in offspring only when paternally transmitted (two cases), while protomutations caused (CTG)n repeats of n > 80 in offspring in 71 cases, of which 56 (78.9%) were paternally transmitted. In conclusion, our data show that paternally transmitted pre- and protomutations were more unstable than maternally transmitted pre- and protomutations. For genetic counseling, this implies that males with a small DMPK mutation have a higher risk of symptomatic offspring compared with females. Consequently, we suggest addressing sex-dependent factors in genetic counseling of small-sized CTG repeat carriers.

Confidential genetic testing and electronic health records: A survey of current practices among Huntington disease testing centers

Background

Clinical care teams providing presymptomatic genetic testing often employ advanced confidentiality practices for documentation and result storage. However, patient requests for increased confidentiality may be in conflict with the legal obligations of medical providers to document patient care activities in the electronic health record (EHR). Huntington disease presents a representative case study for investigating the ways centers currently balance the requirements of EHRs with the privacy demands of patients seeking presymptomatic genetic testing.

Methods

We surveyed 23 HD centers (53% response rate) regarding their use of the EHR for presymptomatic HD testing.

Results

Our survey revealed that clinical care teams and laboratories have each developed their own practices, which are cumbersome and often include EHR avoidance. We found that a majority of HD care teams record appointments in the EHR (91%), often using vague notes. Approximately half of the care teams (52%) keep presymptomatic results of out of the EHR.

Conclusion

As genetic knowledge grows, linking more genes to late‐onset conditions, institutions will benefit from having professional recommendations to guide development of policies for EHR documentation of presymptomatic genetic results. Policies must be sensitive to the ethical differences and patient demands for presymptomatic genetic testing compared to those undergoing confirmatory genetic testing.

A genetic association study of glutamine-encoding DNA sequence structures, somatic CAG expansion, and DNA repair gene variants, with Huntington disease clinical outcomes

BACKGROUND

Huntington disease (HD) is caused by an unstable CAG/CAA repeat expansion encoding a toxic polyglutamine tract. Here, we tested the hypotheses that HD outcomes are impacted by somatic expansion of, and polymorphisms within, the HTT CAG/CAA glutamine-encoding repeat, and DNA repair genes.

METHODS

The sequence of the glutamine-encoding repeat and the proportion of somatic CAG expansions in blood DNA from participants inheriting 40 to 50 CAG repeats within the TRACK-HD and Enroll-HD cohorts were determined using high-throughput ultra-deep-sequencing. Candidate gene polymorphisms were genotyped using kompetitive allele-specific PCR (KASP). Genotypic associations were assessed using time-to-event and regression analyses.

FINDINGS

Using data from 203 TRACK-HD and 531 Enroll-HD participants, we show that individuals with higher blood DNA somatic CAG repeat expansion scores have worse HD outcomes: a one-unit increase in somatic expansion score was associated with a Cox hazard ratio for motor onset of 3·05 (95% CI = 1·94 to 4·80, p = 1·3 × 10^-6). We also show that individual-specific somatic expansion scores are associated with variants in FAN1 (pFDR = 4·8 × 10^-6), MLH3 (pFDR = 8·0 × 10^-4), MLH1 (pFDR = 0·004) and MSH3 (pFDR = 0·009). We also show that HD outcomes are best predicted by the number of pure CAGs rather than total encoded-glutamines.

INTERPRETATION

These data establish pure CAG length, rather than encoded-glutamine, as the key inherited determinant of downstream pathophysiology. These findings have implications for HD diagnostics, and support somatic expansion as a mechanistic link for genetic modifiers of clinical outcomes, a driver of disease, and potential therapeutic target in HD and related repeat expansion disorders.

FUNDING

CHDI Foundation.

Generation of induced pluripotent stem cell line CSSi008-A (4698) from a patient affected by advanced stage of Dentato-Rubral-Pallidoluysian atrophy (DRPLA)

Dentato-Rubral-pallidoluysian atrophy (DRPLA) is a rare autosomal, dominant, progressive neurodegenerative disease that causes involuntary movements, mental and emotional problems. DRPLA is caused by a mutation in the ATN1 gene that encodes for an abnormal polyglutamine stretch in the atrophin-1 protein. DRPLA is most common in the Japanese population, where it has an estimated incidence of 2 to 7 per million people. This condition has also been seen in families from North America and Europe. We obtained a reprogrammed iPSC line from a Caucasian patient with a juvenile onset of the disease, carrying 64 CAG repeat expansion in the ATN1 gene.

Molecular genetic testing laboratory management: emerging challenges for quality assurance

For decades, laboratory managers in the area of molecular genetic testing have struggled to adapt to rapid technological change, growing demand, evolving regulatory frameworks, and frequently changing best practice guidelines. While impressive progress has been made, the scale and scope of these challenges is unlikely to decline in the near future. Instead the challenges are likely to become even more imposing as a result of the emerging new clinical applications, the need for increasingly comprehensive international regulatory and quality assurance frameworks, and the rapidly growing demand for molecular genetic testing in the developing world. All of these challenges can be expected to create new pressures in the areas of cost and efficiency. Efforts to increase the effectiveness and adaptability of quality assurance frameworks should be prioritized with increased attention by scholars, policymakers, and laboratory managers. This review will introduce and familiarize the reader with the basic historical trajectory for the development of quality management frameworks and standardization practices involved in the management of molecular genetic testing laboratories. This review will also identify recurrent dynamics that have posed challenges for quality assurance in the field.

Morphological control of mitochondria as the novel mechanism of Gastrodia elata in attenuating mutant huntingtin-induced protein aggregations

BACKGROUND

According to Compendium of Materia Medica, Gastrodia elata (GE) Blume as a top grade and frequently prescribed herbal medicine has been used in treating dizziness, headaches, and epilepsy, indicating a neuroprotective effect. Because GE is capable of suppressing a hyperactive liver and thus calming endogenous wind, and because Huntington's disease (HD) can be classified as a phenomenon of disturbed liver wind, it is suggested that GE might be beneficial in treating HD. However, although current studies support GE for the prevention of diverse neurodegenerations such as HD, its detailed mechanisms remain elusive.

PURPOSE

To investigate the molecular mechanism of GE in preventing HD by focusing on mitochondrial morphology, which is highly associated with HD etiology and thus proposed as a therapeutic target of neurodegenerations.

STUDY DESIGN/METHODS

The overexpression of the mutant huntingtin (mHTT) gene in rat pheochromocytoma (PC12) cells was used as an in vitro cell model of HD. A filter retardation assay was applied to measure protein aggregations during HTT expression. Cotransfection with mitochondrial fusion and fission genes was used to test their relationships with HTT aggregates by monitoring with a confocal laser scanning microscope and filter retardation assay. Western blot analysis was used to estimate protein expression under different drug treatments or cotransfections with other related genes.

RESULTS

The overexpression of mutant but not normal HTT genes significantly resulted in protein aggregations in PC12 cells. GE dose-dependently attenuated mHTT-induced protein aggregations and free radical formations. GE significantly reversed mHTT-induced mitochondrial fragmentation and dysregulation of mitochondrial fusion and fission molecules. The overexpression of mitochondrial fusion genes attenuated mHTT-induced protein aggregations. Further, Mdivi-1, a DRP1 fission molecule inhibitor, significantly reversed mHTT-induced protein aggregations and mitochondrial fragmentation.

CONCLUSION

GE attenuated mHTT aggregations through the control of mitochondrial fusion and the fission pathway.

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.

Exploring neurologists' perspectives on the return of next generation sequencing results to their patients: a needed step in the development of guidelines

Background

The use of Next Generation Sequencing such as Whole Genome Sequencing (WGS) is a promising step towards a better understanding and treatment of neurological diseases. WGS can result into unexpected information (incidental findings, IFs), and information with uncertain clinical significance. In the context of a Genome Canada project on ‘Personalized Medicine in the Treatment of Epilepsy’, we intended to address these challenges surveying neurologists’ opinions about the type of results that should be returned, and their professional responsibility toward recontacting patients regarding new discovered mutations.

Methods

Potential participants were contacted through professional organizations or direct invitations.

Results

A total of 204 neurologists were recruited. Fifty nine percent indicated that to be conveyed, WGS results should have a demonstrated clinical utility for diagnosis, prognosis or treatment. Yet, 41% deemed appropriate to return results without clinical utility, when they could impact patients’ reproductive decisions, or on patients’ request. Current use of targeted genetic testing and age of patients influenced respondents’ answers. Respondents stated that analysis of genomics data resulting from WGS should be limited to the genes likely to be relevant for the patient’s specific medical condition (69%), so as to limit IFs. Respondents felt responsible to recontact patients and inform them about newly discovered mutations related to the medical condition that triggered the test (75%) for as long as they are following up on the patient (55%). Finally, 53.5% of the respondents felt responsible to recontact and inform patients of clinically significant, newly discovered IFs.

Conclusion

Our results show the importance of formulating professional guidelines sensitive to the various – and sometimes opposite – viewpoints that may prevail within a same community of practice, as well as flexible so as to be attuned to the characteristics of the neurological conditions that triggered a WGS.

Detailed analysis of HTT repeat elements in human blood using targeted amplification-free long-read sequencing

Amplification of DNA is required as a mandatory step during library preparation in most targeted sequencing protocols. This can be a critical limitation when targeting regions that are highly repetitive or with extreme guanine-cytosine (GC) content, including repeat expansions associated with human disease. Here, we used an amplification-free protocol for targeted enrichment utilizing the CRISPR/Cas9 system (No-Amp Targeted sequencing) in combination with single molecule, real-time (SMRT) sequencing for studying repeat elements in the huntingtin (HTT) gene, where an expanded CAG repeat is causative for Huntington disease. We also developed a robust data analysis pipeline for repeat element analysis that is independent of alignment of reads to a reference genome. The method was applied to 11 diagnostic blood samples, and for all 22 alleles the resulting CAG repeat count agreed with previous results based on fragment analysis. The amplification-free protocol also allowed for studying somatic variability of repeat elements in our samples, without the interference of PCR stutter. In summary, with No-Amp Targeted sequencing in combination with our analysis pipeline, we could accurately study repeat elements that are difficult to investigate using PCR-based methods.

Increased nuclear DNA damage precedes mitochondrial dysfunction in peripheral blood mononuclear cells from Huntington's disease patients

Huntington’s disease (HD) is a progressive neurodegenerative disorder primarily affecting the basal ganglia and is caused by expanded CAG repeats in the huntingtin gene. Except for CAG sizing, mitochondrial and nuclear DNA (mtDNA and nDNA) parameters have not yet proven to be representative biomarkers for disease and future therapy. Here, we identified a general suppression of genes associated with aerobic metabolism in peripheral blood mononuclear cells (PBMCs) from HD patients compared to controls. In HD, the complex II subunit SDHB was lowered although not sufficiently to affect complex II activity. Nevertheless, we found decreased level of factors associated with mitochondrial biogenesis and an associated dampening of the mitochondrial DNA damage frequency in HD, implying an early defect in mitochondrial activity. In contrast to mtDNA, nDNA from HD patients was four-fold more modified than controls and demonstrated that nDNA integrity is severely reduced in HD. Interestingly, the level of nDNA damage correlated inversely with the total functional capacity (TFC) score; an established functional score of HD. Our data show that PBMCs are a promising source to monitor HD progression and highlights nDNA damage and diverging mitochondrial and nuclear genome responses representing early cellular impairments in HD.

Dose-Dependent Lowering of Mutant Huntingtin Using Antisense Oligonucleotides in Huntington Disease Patients

On December 11 of 2017, Ionis Pharmaceuticals published a press release announcing dose-dependent reductions of mutant huntingtin protein in their HTTRx Phase 1/2a study in Huntington disease (HD) patients. The results from this Ionis trial have gained much attention from the patient community and the oligonucleotide therapeutics field, since it is the first trial targeting the cause of HD, namely the mutant huntingtin protein, using antisense oligonucleotides (ASOs). The press release also states that the primary endpoints of the study (safety and tolerability) were met, but does not contain data. This news follows the approval of another therapeutic ASO nusinersen (trade name Spinraza) for a neurological disease, spinal muscular atrophy, by the U.S. Food and Drug Administration and European Medicines Agency, in 2016 and 2017, respectively. Combined, this offers hope for the development of the HTTRx therapy for HD patients.

Gastrodia elata alleviates mutant huntingtin aggregation through mitochondrial function and biogenesis mediation

BACKGROUND

According to the Compendium of Materia Medica, Gastrodia elata (GE) Blume is a top-grade herbal medicine frequently used to treat dizziness, headaches, tetanus, and epilepsy, suggesting that it affects neurological functions. Although studies have supported its effects in preventing diverse neurodegenerations such as Huntington's disease (HD), its mechanisms require further investigation.

PURPOSE

To investigate the ability of the molecular mechanism of GE to prevent mutant huntingtin (mHTT) protein aggregation by focusing on mitochondrial function and biogenesis, which have been proposed as the therapeutic targets of HD.

STUDY DESIGN/METHODS

mHtt overexpression in pheochromocytoma (PC12) cells was used as an in vitro cell model of HD. A retardation assay was applied to measure protein aggregation during Htt expression. Cotransfection with transcriptional genes was used to test their relationships with HTT aggregates by monitoring with a confocal laser scanning microscope. Western blot analysis was used to estimate protein expression under different drug treatments or when cotransfected with other related genes.

RESULTS

Mutant, abnormal Htt overexpression resulted in significant protein aggregation in PC12 cells. GE dose-dependently attenuated mHTT aggregates and increased cyclic-AMP response element-binding protein (CREB) phosphorylation. Adenosine A_2A-R receptor (A_2A-R) antagonist counteracted these phenomena. CREB overexpression significantly attenuated mHTT aggregation. GE increased the promoter activity and expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). Furthermore, wild-type PGC-1α but not mutant PGC-1α overexpression attenuated mHTT aggregates.

CONCLUSION

GE attenuated mHtt aggregation by mediating mitochondrial function and biogenesis through the A_2A-R/PKA/CREB/PGC-1α-dependent pathway.

Neuropsychiatric Burden in Huntington's Disease

Huntington's disease is a disorder that results in motor, cognitive, and psychiatric problems. The symptoms often take different forms and the presence of disturbances of the psychic sphere reduces patients' autonomy and quality of life, also impacting patients' social life. It is estimated that a prevalence between 33% and 76% of the main psychiatric syndromes may arise in different phases of the disease, often in atypical form, even 20 years before the onset of chorea and dementia. We present a narrative review of the literature describing the main psychopathological patterns that may be found in Huntington's disease, searching for a related article in the main database sources (Medline, ISI Web of Knowledge, Scopus, and Medscape). Psychiatric conditions were classified into two main categories: affective and nonaffective disorders/symptoms; and anxiety and neuropsychiatric features such as apathy and irritability. Though the literature is extensive, it is not always convergent, probably due to the high heterogeneity of methods used. We summarize main papers for pathology and sample size, in order to present a synoptic vision of the argument. Since the association between Huntington's disease and psychiatric symptoms was demonstrated, we argue that the prevalent and more invalidating psychiatric components should be recognized as early as possible during the disease course in order to best address psychopharmacological therapy, improve quality of life, and also reduce burden on caregivers.

Data Analytics from Enroll-HD, a Global Clinical Research Platform for Huntington's Disease

Background

The study of complex neurodegenerative diseases is moving away from hypothesis-driven biological methods toward large scale multimodal approaches, requiring standardized collaborative efforts. Enroll-HD exemplifies such an integrated clinical research platform, designed and implemented to meet the research and clinical needs of Huntington's disease (HD). The aim of this study was to describe the unique organization of Enroll-HD and report baseline data analyses of its core study.

Methods

The Enroll-HD platform incorporates electronic data capture, biosampling, and a longitudinal observational study spanning four continents (ClinicalTrials.gov Identifier: NCT01574053). The primary study population includes HD gene expansion carriers (HDGECs; CAG expansion ≥36), subdivided into manifest/premanifest HD. The control population consists of genotype-negative first-degree relatives and family controls not genetically related. The study includes 10 core clinical assessments covering motor, cognitive, and behavioral domains.

Results

This data set comprises 1,534 participants (HDGEC = 1,071; controls = 463). Participant retention was high; 42 participants prematurely withdrew from the study. Mean ± standard deviation SD CAG repeat size was 43.5 ± 3.5 for HDGECs and 19.8 ± 3.4 for controls. Motor and behavioral assessments identified numerical differences between controls and HDGECs (manifest > premanifest > controls). Functional and independence assessments were generally similar for the premanifest and control groups with overlap in range of scores obtained. For the majority of cognitive tests, there were large differences between participants with manifest HD and all other groups.

Conclusions

These first data from the Enroll-HD clinical research platform demonstrate the maturity and potential of the platform in collecting high-quality, clinically relevant data. Future data sets will be substantially larger as the platform expands longitudinally and regionally.

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.

Association of status redox with demographic, clinical and imaging parameters in patients with Huntington's disease

Huntington's disease (HD) is an autosomal dominant, progressive neurodegenerative disorder, caused by an expanded trinucleotide CAG sequence of the huntingtin (Htt) gene, which encodes a stretch of glutamines in the Htt protein. The mechanisms of neurodegeneration associated with the accumulation of Htt aggregates still remains unclear.

OBJECTIVES

To determine oxidative stress biomarkers in HD patients and their relationship with clinical, demographic and neuroimaging parameters.

DESIGN AND METHODS

Fourteen patients and 39 controls paired by age and sex participated in this study. Oxidative damage was assayed in blood by measuring malondialdehyde (MDA) and advanced oxidative protein products (AOPPs). Antioxidant status was determined by activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), reduced glutathione (GSH), protein thiols and total antioxidant capacity (FRAP). The Unified Huntington Disease Rating Scale (UHDRS) and neuroimaging studies were also employed.

RESULTS

MDA, AOPP and GPx were significantly increased in HD patients with respect to the control group, while GR activity was decreased. FRAP correlated with age of disease onset, AOPP with motor severity (UHDRS score), age of patients and age of disease onset. Caudate atrophy was associated with lower plasma concentrations of GSH.

CONCLUSIONS

These findings point to a redox imbalance in HD patients. GR activity could be a potential biomarker for symptom onset in asymptomatic gene carriers, while plasmatic GSH could be useful in monitoring the progression of neurodegeneration - as an expression of caudate atrophy - during the course of the disease.

[Huntington's disease]

BACKGROUND

Huntington's disease (HD) is a progressive neurodegenerative disorder characterized by hyperkinetic movements, psychiatric (e.g. depression and psychosis) and cognitive symptoms (frontal lobe dementia). In Germany approximately 8000 patients suffer from HD.

OBJECTIVES

The paper reviews the clinical course, epidemiology, genetics, differential diagnoses, pathophysiology, symptomatics and causal treatment options.

METHODS

Publications on animal and human HD studies and trials and reviews available in Medline have been taken into account.

RESULTS

Only genetic testing allows diagnostic certainty. The CAG repeat length influences age of onset, disease course and life expectancy. The mechanism by which mutant huntingtin protein (mHTT) causes HD is complex and poorly understood but leads to cell death, in particular in striatal neurons. In clinical trials antioxidants (e.g. coenzyme Q10), selisistat, PBT2, cysteamine, N-methyl-D-aspartate (NMDA)-receptor antagonists and tyrosine kinase B receptor agonists have been studied in HD.

CONCLUSION

No disease-modifying therapy is currently available for HD; however, gene silencing, e.g. through RNA interference, is a promising technique which could lead to effective therapies in due course.

Making (anti-) sense out of huntingtin levels in Huntington disease

Background

Huntington disease (HD) is an autosomal dominant neurodegenerative disorder, characterized by motor, psychiatric and cognitive symptoms. HD is caused by a CAG repeat expansion in the first exon of the HTT gene, resulting in an expanded polyglutamine tract at the N-terminus of the huntingtin protein. Typical disease onset is around mid-life (adult-onset HD) whereas onset below 21 years is classified as juvenile HD. While much research has been done on the underlying HD disease mechanisms, little is known about regulation and expression levels of huntingtin RNA and protein.

Results

In this study we used 15 human post-mortem HD brain samples to investigate the expression of wild-type and mutant huntingtin mRNA and protein. In adult-onset HD brain samples, there was a small but significantly lower expression of mutant huntingtin mRNA compared to wild-type huntingtin mRNA, while wild-type and mutant huntingtin protein expression levels did not differ significantly. Juvenile HD subjects did show a lower expression of mutant huntingtin protein compared to wild-type huntingtin protein. Our results in HD brain and fibroblasts suggest that protein aggregation does not affect levels of huntingtin RNA and protein. Additionally, we did not find any evidence for a reduced expression of huntingtin antisense in fibroblasts derived from a homozygous HD patient.

Conclusions

We found small differences in allelic huntingtin mRNA levels in adult-onset HD brain, with significantly lower mutant huntingtin mRNA levels. Wild-type and mutant huntingtin protein were not significantly different in adult-onset HD brain samples. Conversely, in juvenile HD brain samples mutant huntingtin protein levels were lower compared with wild-type huntingtin, showing subtle differences between juvenile HD and adult-onset HD. Since most HD model systems harbor juvenile repeat expansions, our results suggest caution with the interpretation of huntingtin mRNA and protein studies using HD cell and animal models with such long repeats. Furthermore, our huntingtin antisense results in homozygous HD cells do not support reduced huntingtin antisense expression due to an expanded CAG repeat.

Evaluating the SERCA2 and VEGF mRNAs as Potential Molecular Biomarkers of the Onset and Progression in Huntington's Disease

Abnormalities of intracellular Ca²⁺ homeostasis and signalling as well as the down-regulation of neurotrophic factors in several areas of the central nervous system and in peripheral tissues are hallmarks of Huntington’s disease (HD). As there is no therapy for this hereditary, neurodegenerative fatal disease, further effort should be made to slow the progression of neurodegeneration in patients through the definition of early therapeutic interventions. For this purpose, molecular biomarker(s) for monitoring disease onset and/or progression and response to treatment need to be identified. In the attempt to contribute to the research of peripheral candidate biomarkers in HD, we adopted a multiplex real-time PCR approach to analyse the mRNA level of targeted genes involved in the control of cellular calcium homeostasis and in neuroprotection. For this purpose we recruited a total of 110 subjects possessing the HD mutation at different clinical stages of the disease and 54 sex- and age-matched controls. This study provides evidence of reduced transcript levels of sarco-endoplasmic reticulum-associated ATP2A2 calcium pump (SERCA2) and vascular endothelial growth factor (VEGF) in peripheral blood mononuclear cells (PBMCs) of manifest and pre-manifest HD subjects. Our results provide a potentially new candidate molecular biomarker for monitoring the progression of this disease and contribute to understanding some early events that might have a role in triggering cellular dysfunctions in HD.

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.

Genetics of Huntington's disease and related disorders

Huntington's disease is the most frequent form of the hereditary choreas and has a multifaceted phenotype including cognitive and psychiatric impairment. The disorder is due to a dynamic mutation, which also influences the onset age of the disorder. Other genetic modifiers of the HD phenotypes have been suggested but often not confirmed by independent studies. Several syndromes with similar presentation have different genetic backgrounds, including the neuroacanthocytoses, mainly choreoacanthocytosis and MacLeod syndrome as a result of mutations in chorein and Kell protein, respectively, but also benign hereditary chorea, owing to mutations in NKX-2-1, and paroxysmal kinesigenic dyskinesia, as a result of recently found mutations in the proline-rich transmembrane protein 2, PRRT2. Chorea can also be a major feature in other neurogenetic disorders, including the spinocerebellar ataxias and also in neurometabolic disorders.

Recent advances in the management of choreas

The management of patients with chorea, in particular Huntington's disease, is a complex task requiring skills in a number of areas. This paper reviews new knowledge on this topic and places it in the context of established procedures. It is focused on Huntington's disease, since this is the disorder, for which most publications on management have been published in the past few years. Management starts with appropriate diagnosis and differential diagnosis, with the aim of finding disorders with chorea amenable to causative treatment. The place of genetic testing and the importance of genetic counselling is stressed, as well as the importance of precise observation in the course of the disorder to tailor appropriate therapies. Pharmacological treatment is based on poor evidence but to a large extent on expertise from centres devoted to the care of patients with Huntington's disease. It is focused mainly on motor and psychiatric aspects of the phenotype. Nonpharmacological treatment is important and is best offered in a multidisciplinary care setting.