Genetic screening for Huntington disease phenocopies in Sweden: A tertiary center case series focused on short tandem repeat (STR) disorders.

OBJECTIVE: To perform a screening for Huntington disease (HD) phenocopies in a Swedish cohort. METHODS: Seventy-three DNA samples negative for HD were assessed at a tertiary center in Stockholm. The screening included analyses for C9orf72-frontotemporal dementia/amyotrophic lateral sclerosis (C9orf72-FTD/ALS), octapeptide repeat insertions (OPRIs) in PRNP associated with inherited prion diseases (IPD), Huntington's disease-like 2 (HDL2), spinocerebellar ataxia-2 (SCA2), spinocerebellar ataxia 3 (SCA3) and spinocerebellar ataxia-17 (SCA17). Targeted genetic analysis was carried out in two cases based on the salient phenotypic features. RESULTS: The screening identified two patients with SCA17, one patient with IPD associated with 5-OPRI but none with nucleotide expansions in C9orf72 or for HDL2, SCA2 or SCA3. Furthermore, SGCE-myoclonic-dystonia 11 (SGCE-M-D) and benign hereditary chorea (BHC) was diagnosed in two sporadic cases. WES identified VUS in STUB1 in two patients with predominant cerebellar ataxia. CONCLUSIONS: Our results are in keeping with previous screenings and suggest that other genes yet to be discovered are involved in the etiology of HD phenocopies.

Plasma biomarker profiles in autosomal dominant Alzheimer's disease.

Emerging plasma biomarkers of Alzheimer's disease might be non-invasive tools to trace early Alzheimer's disease-related abnormalities such as the accumulation of amyloid-beta peptides, neurofibrillary tau tangles, glial activation and neurodegeneration. It is, however, unclear which pathological processes in the CNS can be adequately detected by peripheral measurements and whether plasma biomarkers are equally applicable in both clinical and preclinical phases. Here we aimed to explore the timing and performance of plasma biomarkers in mutation carriers compared to non-carriers in autosomal dominant Alzheimer's disease. Samples (n = 164) from mutation carriers (n = 33) and non-carriers (n = 42) in a Swedish cohort of autosomal dominant Alzheimer's disease (APP p.KM670/671NL, APP p.E693G and PSEN1 p.H163Y) were included in explorative longitudinal analyses. Plasma phosphorylated tau (P-tau181), total tau (T-tau), neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP) concentrations were measured with a single-molecule array method as previously described. Plasma biomarkers were additionally correlated to Alzheimer's disease core biomarkers in the CSF. Results from the longitudinal analyses confirmed that plasma P-tau181, NfL and GFAP concentrations were higher in mutation carriers compared to non-carriers. This change was observed in the presymptomatic phase and detectable first as an increase in GFAP approximately 10 years before estimated symptom onset, followed by increased levels of P-tau181 and NfL closer to expected onset. Plasma P-tau181 levels were correlated to levels of P-tau181 and T-tau in the CSF. Altogether, plasma P-tau181, GFAP and NfL seem to be feasible biomarkers to detect different Alzheimer's disease-related pathologies already in presymptomatic individuals. Interestingly, changes in plasma GFAP concentrations were detected prior to P-tau181 and NfL. Our results suggest that plasma GFAP might reflect Alzheimer's disease pathology upstream to accumulation of tangles and neurodegeneration. The implications of these findings need additional validation, in particular because of the limited sample size.

APOE ε4 influences cognitive decline positively in APP and negatively in PSEN1 mutation carriers with autosomal-dominant Alzheimer's disease.

BACKGROUND AND PURPOSE: The aim was to investigate the effect of APOE ε4 allele on cognitive decline in adAD. Presence of the APOE ε4 allele reduces age of symptom onset, increases disease progression, and lowers cognitive performance in sporadic Alzheimer's disease (AD), while the impact of the APOE ε4 allele in autosomal-dominant AD (adAD) is incompletely known. METHODS: Mutation carriers (MCs; n = 39) and non-carriers (NCs; n = 40) from six adAD families harbouring a mutation in the APP (28 MCs and 25 NCs) or the PSEN1 genes (11 MCs and 15 NCs) underwent repeated cognitive assessments. A timeline of disease course was defined as years to expected age of clinical onset (YECO) based on history of disease onset in each family. The MC and NC groups were comparable with regard to demographics and prevalence of the APOE ε4 allele. The relationship between cognitive decline and YECO, YECO2 , education, APOE, and APOE-by-YECO interaction was analysed using linear mixed-effects models. RESULTS: The trajectory of cognitive decline was significantly predicted by linear and quadratic YECO and education in MCs and was determined by age and education in NCs. Adding APOE ε4 allele (presence/absence) as a predictor did not change the results in the MC and NC groups. The outcome also remained the same for MCs and NCs after adding the APOE-by-YECO interaction as a predictor. Analyses of APP and PSEN1 MCs separately showed favourable APOE-by-YECO interaction in APP (less steep decline) and unfavourable interaction in PSEN1 (steeper decline), linked to the APOE ε4 allele. CONCLUSION: The APOE ε4 allele influences cognitive decline positively in APP and negatively in PSEN1 mutation carriers with adAD, indicating a possible antagonistic pleiotropy.

TBK1 haploinsufficiency results in changes in the K63-ubiquitination profiles in brain and fibroblasts from affected and presymptomatic mutation carriers.

BACKGROUND: Frontotemporal dementia (FTD) is a neurodegenerative disease, resulting in progressive problems in language and/or behaviour and is often diagnosed before 65 years of age. Ubiquitin positive protein aggregates in the brain are among the key pathologic hallmarks of frontotemporal lobar degeneration (FTLD) postmortem. The TANK-binding kinase 1 gene (TBK1) is on the list of genes that can contribute to the development of FTD as well as the related neurodegenerative disease amyotrophic lateral sclerosis (ALS). METHODS: In this study, using an array of clinical and neuropathological data combined with biochemical and proteomics assays, we analyze the TBK1 splice-mutation (c.1340 + 1G > A) in a Swedish family with a history of FTD and ALS. We also explore the K63 ubiquitination landscape in post-mortem brain tissue and fibroblast cultures. RESULTS: The intronic (c.1340 + 1G > A) mutation in TBK1 results in haploinsufficiency and affects the activity of the protein in symptomatic and pre-symptomatic mutation carriers. CONCLUSION: Our results suggest that the mutation leads to a significant reduction of TBK1 activity and induce alterations in K63 ubiquitination profile of the cell already in the presymptomatic stages.

Single-cell multimodal analysis in a case with reduced penetrance of Progranulin-Frontotemporal Dementia.

We identified an autosomal dominant progranulin mutation carrier without symptoms of dementia in her lifetime (Reduced Penetrance Mutation Carrier, RedPenMC). This resistance to develop expected pathology presents a unique opportunity to interrogate neurodegenerative mechanisms. We performed multimodal single-nuclei analyses of post-mortem frontal cortex from RedPenMC, including transcriptomics and global levels of chromatin marks. RedPenMC had an increased ratio of GRN-expressing microglia, higher levels of activating histone mark H3k4me3 in microglia and lower levels of the repressive chromatin marks H3k9me1 and H3k9me3 in the frontal cortex than her affected mutation carrier son and evidence of higher protein levels of progranulin in both plasma and brain homogenates. Although the study is limited to one case, the results support that restoring brain progranulin levels may be sufficient to escape neurodegeneration and FTD. In addition to previously identified modifier genes, it is possible that epigenetic marks may contribute to the increased progranulin expression in cases of reduced penetrance. These findings may stimulate similar follow-up studies and new therapeutic approaches.

Ataxin-2 gene: a powerful modulator of neurological disorders.

PURPOSE OF REVIEW: To provide an update on the role of Ataxin-2 gene (ATXN2) in health and neurological diseases. RECENT FINDINGS: There is a growing complexity emerging on the role of ATXN2 and its variants in association with SCA2 and several other neurological diseases. Polymorphisms and intermediate alleles in ATXN2 establish this gene as a powerful modulator of neurological diseases including lethal neurodegenerative conditions such as motor neuron disease, spinocerebellar ataxia 3 (SCA3), and peripheral nerve disease such as familial amyloidosis polyneuropathy. This role is in fact far wider than the previously described for polymorphism in the prion protein (PRNP) gene. Positive data from antisense oligo therapy in a murine model of SCA2 suggest that similar approaches may be feasible in humans SCA2 patients. SUMMARY: ATXN2 is one of the few genes where a single gene causes several diseases and/or modifies several and disparate neurological disorders. Hence, understanding mutagenesis, genetic variants, and biological functions will help managing SCA2, and several human diseases connected with dysfunctional pathways in the brain, innate immunity, autophagy, cellular, lipid, and RNA metabolism.

Plasma metabolomics of presymptomatic PSEN1-H163Y mutation carriers: a pilot study.

BACKGROUND AND OBJECTIVE: PSEN1-H163Y carriers, at the presymptomatic stage, have reduced 18 FDG-PET binding in the cerebrum of the brain (Scholl et al., Neurobiol Aging 32:1388-1399, 2011). This could imply dysfunctional energy metabolism in the brain. In this study, plasma of presymptomatic PSEN1 mutation carriers was analyzed to understand associated metabolic changes. METHODS: We analyzed plasma from noncarriers (NC, n = 8) and presymptomatic PSEN1-H163Y mutation carriers (MC, n = 6) via untargeted metabolomics using gas and liquid chromatography coupled with mass spectrometry, which identified 1199 metabolites. All the metabolites were compared between MC and NC using univariate analysis, as well as correlated with the ratio of Aß1-42/A ß 1-40 , using Spearman's correlation. Altered metabolites were subjected to Ingenuity Pathway Analysis (IPA). RESULTS: Based on principal component analysis the plasma metabolite profiles were divided into dataset A and dataset B. In dataset A, when comparing between presymptomatic MC and NC, the levels of 79 different metabolites were altered. Out of 79, only 14 were annotated metabolites. In dataset B, 37 metabolites were significantly altered between presymptomatic MC and NC and nine metabolites were annotated. In both datasets, annotated metabolites represent amino acids, fatty acyls, bile acids, hexoses, purine nucleosides, carboxylic acids, and glycerophosphatidylcholine species. 1-docosapentaenoyl-GPC was positively correlated, uric acid and glucose were negatively correlated with the ratio of plasma Aß1-42 /Aß1-40 (P < 0.05). INTERPRETATION: This study finds dysregulated metabolite classes, which are changed before the disease symptom onset. Also, it provides an opportunity to compare with sporadic Alzheimer's Disease. Observed findings in this study need to be validated in a larger and independent Familial Alzheimer's Disease (FAD) cohort.

A Novel Duplication in ATXN2 as Modifier for Spinocerebellar Ataxia 3 (SCA3) and C9ORF72-ALS.

BACKGROUND: The ataxin-2 (ATXN2) gene contains a cytosine-adenine-guanine repeat sequence ranging from 13 to 31 repeats, but when surpassing certain thresholds causes neurodegeneration. Genetic alterations in ATXN2 other than pathological cytosine adenine guanine (CAG) repeats are unknown. METHODS/RESULTS: We have identified a 9-base pair duplication in the 2-gene ATXN2 sense/antisense region. The duplication was found in a Swedish family with spinocerebellar ataxia 3 with parkinsonism, conferring a deviated age at onset unexplained by the concomitant presence of ATXN2 intermediate alleles. Similarly, C9ORF72 amyotrophic lateral sclerosis cases bearing the same duplication had earlier age at onset than those with C9ORF72 and ATXN2 intermediate alleles. No effect was evident in Parkinson's disease (PD) cases without known PD gene mutations. CONCLUSIONS: We describe the first genetic alteration other than the known intermediate-range CAG repeats in ATXN2. This 9-base pair duplication may act as an additional hit among carriers of pathological nucleotide expansions in ATXN3 and C9ORF72 with ATXN2 intermediate. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Novel Features and Abnormal Pattern of Cerebral Glucose Metabolism in Spinocerebellar Ataxia 19.

Spinocerebellar ataxia type 19 (SCA19), allelic with spinocerebellar ataxia type 22 (SCA22), is a rare syndrome caused by mutations in the KCND3 gene which encodes the potassium channel Kv4.3. Only 18 SCA19/22 families and sporadic cases of different ethnic backgrounds have been previously reported. As in other SCAs, the SCA19/22 phenotype is variable and usually consists of adult-onset slowly progressive ataxia and cognitive impairment; myoclonus and seizures; mild Parkinsonism occurs in some cases. Here we describe a Swedish SCA19/22 family spanning five generations and harboring the T377M mutation in KCND3. For the first time for this disease, 18F-fluorodeoxyglucose PET was assessed revealing widespread brain hypometabolism. In addition, we identified white matter abnormalities and found unusual features for SCA19/22 including early age of onset and fast rate of progression in the late course of disease in the oldest patient of this family.

Buccal Cell Micronucleus Frequency Is Significantly Elevated in Patients with Spinocerebellar Ataxia Type 2.

Spinocerebellar ataxia type 2 (SCA2) is part of a group of at least nine dominantly inherited disorders characterized by progressive degeneration of specific neuronal populations and a shared mutational mechanism involving the expansion of a CAG repeat tract in coding regions of novel genes. Efforts have been made to identify biomarkers of disease progression, which would allow timely preventive therapeutic interventions. In the present study was assessed the influence of several genome instability biomarkers on SCA2 clinical severity. A case-control design was applied on exfoliated epithelial buccal cells to determine micronuclei frequency and others nuclear anomalies, using 5% Giemsa stains. The slides were analyzed under 1000X magnification and nuclei morphological anomalies were identified according to Tolbert PE, et al. (1992) and Bolognesi C, et al. (2013) criteria. It was found a highly significant increase in micronuclei frequency in cases related to age and sex-matched healthy controls (p <0.001). There was a trend for karyolytic, pyknotic and condensed chromatin cells to be increased in SCA2 cases, and a significant association was found between binucleated cells and disease duration (r = 0.46; p = 0.027). Nor the CAG repeat length neither the age at onset correlated significantly with any of the studied markers (p >0.05). Our results are consistent with report previous in similar neurodegenerative diseases, and suggest that micronuclei and binucleated cells constitute potential peripheral biomarkers for SCA2. These results should be validated by other studies.

Correlations Between Methionine Cycle Metabolism, COMT Genotype, and Polyneuropathy in L-Dopa Treated Parkinson's Disease: A Preliminary Cross-Sectional Study.

BACKGROUND: Polyneuropathy (pnp) is recognized as a clinical feature of Parkinson's disease (PD). Whether pnp is a result of the alpha-synucleinopathy or related to treatment is debated. Previous studies support underlying disturbances in the methionine cycle mediated by L-dopa. OBJECTIVE: Describe possible relationships between methionine cycle metabolism and the development of pnp in L-dopa treated PD. Furthermore, we aim to investigate possible genetic risk factors by genotyping specific SNPs in enzymes involved in the abovementioned pathways. METHODS: In a cross-sectional study design, L-dopa treated PD patients (n = 33) and controls (n = 16) were evaluated with biochemical and genetic analyses. Subjects were assessed clinically and with regards to signs of pnp using established clinical neuropathy rating scales. RESULTS: 16/33 patients fulfilled a study diagnosis of pnp compared to 0 age-matched controls. Levels of homocysteine (Hcy) were significantly higher in patients with pnp (n = 16) compared to controls. A significant correlation between neuropathy scores and Hcy was seen in the whole patient group (n = 33). A significant difference in the genotype distribution of the COMT A158G polymorphism was demonstrated, favoring the low activity genotype in patients with pnp compared to both controls and patients without pnp. CONCLUSIONS: Pnp is a prevalent condition in L-dopa treated PD and an association may exist with elevated levels of Hcy, possibly reflecting an underlying impaired cellular methylation capacity. Furthermore, an association may exist between the low activity COMT genotype and pnp. These preliminary findings and the suggested pathophysiological mechanisms should be confirmed in future large-scale studies.

Prodromal spinocerebellar ataxia type 2: Prospects for early interventions and ethical challenges.

The characterization of prodromal stages in neurodegenerative disorders is becoming increasingly important because of the need for early neuroprotective therapies. Research during the past 3 decades in spinocerebellar ataxia type 2 has revealed a large body of evidence suggesting that many disease features precede the manifest cerebellar syndrome, which delineates the prodromal stage of this disorder. This stage is defined by clinical, imaging, and functional criteria, which are supported by early molecular events demonstrated in animal models. Knowledge regarding prodromal spinocerebellar ataxia type 2 provides insight into the mechanisms underlying neurodegeneration from the early stages, which enables the design of promising disease-modifying clinical trials through the identification of the optimum moment to begin the therapies, the appropriate selection of individuals, and the identification of sensitive outcome measures. The management of patients in prodromal spinocerebellar ataxia type 2 may raise ethical dilemmas related to predictive diagnosis and early interventions, which impose new challenges to clinical and therapeutic research. © 2017 International Parkinson and Movement Disorder Society.

Association of glutathione S-transferase omega polymorphism and spinocerebellar ataxia type 2.

BACKGROUND: Spinocerebellar ataxia type 2 is a neurodegenerative disorder caused by a CAG repeat expansion in ATXN2 gene. There is high clinical variability among affected patients suggesting the occurring of modifier genes influencing the clinical phenotype. OBJECTIVE: The objective is to assess the association of GSTO1 rs4925 and GSTO2 rs2297235 SNPs on the clinical phenotype in SCA2 patients. METHODS: A case-control study was performed in a sample of 120 SCA2 Cuban patients and 100 healthy subjects. Age at onset, 60° Maximal Saccade Velocity and SARA score were used as clinical markers. GSTO1 rs4925 and GSTO2 rs2297235 SNPs were determined by PCR/RFLP. RESULTS: Distribution of the GSTO1 alleles and genotypes was nearly equal between the control group and SCA2 patients. GSTO1 genotypes were not associated to clinical markers in SCA2 patients. Distribution of the GSTO2 "G" allele and "AG" genotype differed significantly between SCA2 patients and controls. Symptomatic SCA2 individuals had a 2.29-fold higher chance of carrying at least one "G" allele at GSTO2 rs2297235 than controls (OR=2.29, 95% CI: 1.29-4.04). GSTO2 genotypes were significantly associated to age at onset (p=0.037) but not to 60° Maximal Saccade Velocity or SARA score in SCA2 patients. CONCLUSION: The GSTO1 rs4925 polymorphism is not associated to SCA2. Meanwhile, the GSTO2 rs2297235 "AG" genotype is associated to SCA2 but failed to show any association with clinical markers, with the exception of a potential association with the age at disease onset.

Epidemiological, clinical, and molecular characterization of Cuban families with spinocerebellar ataxia type 3/Machado-Joseph disease.

BACKGROUND: Spinocerebellar Ataxia Type 3/Machado-Joseph Disease (SCA3/MJD) is a hereditary neurodegenerative disorder resulting from the expansion of CAG repeats in the ATXN3 gene. It is the most common autosomal dominant ataxia in the world, but its frequency prevalence in Cuba remains uncertain. We undertook a national study in order to characterize the ATXN3 gene and to determine the prevalence of SCA3/MJD in Cuba. RESULTS: Twenty-two individuals belonging to 8 non-related families were identified as carriers of an expanded ATXN3 allele. The affected families come from the central and western region of the country. Ataxia of gait was the initial symptom in all of the cases. The normal alleles ranged between 14 and 33 CAG repeats while the expanded ones ranged from 63 to 77 repeats. The mean age at onset was 40 ± 9 years and significantly correlated with the number of CAG repeats in the expanded alleles. CONCLUSIONS: This disorder was identified as the second most common form of spinocerebellar ataxia (SCA) in Cuba based on molecular testing, and showing a different geographical distribution from that of SCA2. This research constitutes the first clinical and molecular characterization of Cuban SCA3 families, opening the way for the implementation of predictive diagnosis for at risk family members.

SCA2 predictive testing in Cuba: challenging concepts and protocol evolution.

Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disease caused by a CAG repeat expansion in the ATXN2 gene. Cuba has the highest prevalence (6.57 cases/10(5) inhabitants) of SCA2 in the world. The existence of 753 affected individuals and 7173 relatives at risk prompted the development in 2001 of the first predictive testing program in the country. The medical records of over 1193 individuals, who requested the test within a 13-year period, were analyzed retrospectively. The presymptomatic and the prenatal tests had uptake rates of 43.4 and 23.9 %, respectively. Several ethical challenges resulted from this program. These include the following: (1) withdrawal due to the initial protocol's length; (2) the request to participate by 16 at-risk adolescents; (3) the decision made by ten out of 33 couples with a test-positive fetus to carry the pregnancy to term, leading to de facto predictive testing of minors; (4) the elevated frequency of the ATXN2 gene large normal alleles (≥23 to 31 repeats) in the reference population. These issues have led to major changes in the guidelines of the predictive testing protocol: (1) the protocol length was shortened; (2) the inclusion criteria were expanded to reach at-risk adolescents with an interest in prenatal diagnosis; (3) interdisciplinary follow-up was offered to families in which test-positive fetuses were not aborted; (4) prenatal testing was made available to carriers of large normal alleles with ≥27 CAG repeats. The profiles of the participants were similar to those reported for other predictive testing programs for conditions like Huntington disease and familial adenomatous polyposis. The genetic counseling practices at the community level, the ample health education provided to the at-risk population, together with multidisciplinary and specialized attention to the affected families, are lessons from the Cuban experience that can be relevant for other international teams conducting predictive testing for other late-onset neurodegenerative disorders.

Herencia epigenética (metilación del ácido desoxirribonucleico): contexto clínico en neurodegeneraciones y gen ATXN2 / Epigenetic heredity (deoxyribonucleic acid methylation): Clinical context in neurodegenerative disorders and ATXN2 gene

La epigenética es el colectivo de cambios en el fenotipo debidos a procesos que surgen independientes de la secuencia primaria del ADN. Está íntimamente relacionada con los cambios en los niveles y perfiles de expresión de los genes. Estos cambios están mediados por las modificaciones en las colas de histonas cromatineanas, la metilación del ADN, los micro-ARN y la remodelación de la cromatina, constituyendo los fundamentos de la herencia epigenética. La metilación del ADN involucra la adición del grupo metilo a la citosina del ADN genómico. Esta reacción es mediada por las enzimas metiltransferasas. La metilación regula la expresión génica, reprimiendo la transcripción, en tanto que su ausencia activa la expresión. Varias enfermedades humanas, como el cáncer, la enfermedad de Alzheimer, el ictus, el Parkinson o la diabetes mellitus tipo 2, están vinculadas a procesos epigenéticos. En este trabajo se presentan las bases de la herencia epigenética con énfasis en la metilación del ADN. También se ilustran los mecanismos patogénicos que relacionan a la epigenética con varias enfermedades humanas y, más específicamente, las neurodegeneraciones. Discutimos los conceptos actuales para poder entender la contribución de la epigenética en enfermedades neurodegenerativas. Se enfatiza en los hallazgos obtenidos por nuestro laboratorio y otros investigadores en el gen ATXN2, causante de la ataxia espinocerebelosa tipo 2 y otras enfermedades neurodegenerativas, como la esclerosis lateral amiotrófica. Los procesos epigenéticos desempeñan un rol primordial en la patogénesis de varias enfermedades humanas y en varias neurodegeneraciones. Este conocimiento ha impulsado un desarrollo tecnológico en las técnicas de análisis de los patrones de metilación y se proyectará al área terapéutica(AU)

Epigenetics is the group of changes in the phenotype which are related with the process independently of the primary DNA sequence. These changes are intimately related with changes in the gene expression level and its profile across the body. These are mediated by histone tail modifications, DNA methylation, micro-RNAs, with chromatin remodeling remaining as the foundation of epigenetic changes. DNA methylation involves the covalent addition of methyl group to cytosine of the DNA, which is mediated by methyltransferases enzymes. DNA methylation regulates gene expression by repressing transcription, while de-methylation activates gene transcription. Several human diseases are related with the epigenetic process: cancer, Alzheimer disease, stroke, Parkinson disease, and diabetes. We present here the basis of epigenetic inheritance and show the pathogenic mechanisms relating epigenetics in human diseases, specifically with regard to neurodegeneration. We discuss current concepts aimed at understanding the contribution of epigenetics to human neurodegenerative diseases. We also discuss recent findings obtained in our and other centers regarding the ATXN2 gene that causes spinocerebellar ataxia 2 and amyotrophic lateral sclerosis. Epigenetics play a pivotal role in the pathogenesis of human diseases and in several neurodegenerative disorders, and this knowledge will illuminate the pathways in the diagnostic and therapeutic field, which ultimately will be translated into the clinic context ofneurodegenerative diseases (AU)