A non-synonymous single nucleotide polymorphism in SIRT6 predicts neurological severity in Friedreich ataxia.

Introduction: Friedreich ataxia (FRDA) is a recessive neurodegenerative disease characterized by progressive ataxia, dyscoordination, and loss of vision. The variable length of the pathogenic GAA triplet repeat expansion in the FXN gene in part explains the interindividual variability in the severity of disease. The GAA repeat expansion leads to epigenetic silencing of FXN; therefore, variability in properties of epigenetic effector proteins could also regulate the severity of FRDA. Methods: In an exploratory analysis, DNA from 88 individuals with FRDA was analyzed to determine if any of five non-synonymous SNPs in HDACs/SIRTs predicted FRDA disease severity. Results suggested the need for a full analysis at the rs352493 locus in SIRT6 (p.Asn46Ser). In a cohort of 569 subjects with FRDA, disease features were compared between subjects homozygous for the common thymine SIRT6 variant (TT) and those with the less common cytosine variant on one allele and thymine on the other (CT). The biochemical properties of both variants of SIRT6 were analyzed and compared. Results: Linear regression in the exploratory cohort suggested that an SNP (rs352493) in SIRT6 correlated with neurological severity in FRDA. The follow-up analysis in a larger cohort agreed with the initial result that the genotype of SIRT6 at the locus rs352493 predicted the severity of disease features of FRDA. Those in the CT SIRT6 group performed better on measures of neurological and visual function over time than those in the more common TT SIRT6 group. The Asn to Ser amino acid change resulting from the SNP in SIRT6 did not alter the expression or enzymatic activity of SIRT6 or frataxin, but iPSC-derived neurons from people with FRDA in the CT SIRT6 group showed whole transcriptome differences compared to those in the TT SIRT6 group. Conclusion: People with FRDA in the CT SIRT6 group have less severe neurological and visual dysfunction than those in the TT SIRT6 group. Biochemical analyses indicate that the benefit conferred by T to C SNP in SIRT6 does not come from altered expression or enzymatic activity of SIRT6 or frataxin but is associated with changes in the transcriptome.

Randomized, double-blind, placebo-controlled study of interferon-γ 1b in Friedreich Ataxia.

Objective: In vitro, in vivo, and open-label studies suggest that interferon gamma (IFN-γ 1b) may improve clinical features in Friedreich Ataxia through an increase in frataxin levels. The present study evaluates the efficacy and safety of IFN-γ 1b in the treatment of Friedreich Ataxia through a double-blind, multicenter, placebo-controlled trial. Methods: Ninety-two subjects with FRDA between 10 and 25 years of age were enrolled. Subjects received either IFN-γ 1b or placebo for 6 months. The primary outcome measure was the modified Friedreich Ataxia Rating Scale (mFARS). Results: No difference was noted between the groups after 6 months of treatment in the mFARS or secondary outcome measures. No change was noted in buccal cell or whole blood frataxin levels. However, during an open-label extension period, subjects had a more stable course than expected based on natural history data. Conclusions: This study provides no direct evidence for a beneficial effect of IFN-γ1b in FRDA. The modest stabilization compared to natural history data leaves open the possibility that longer studies may demonstrate benefit.

Longitudinal analysis of contrast acuity in Friedreich ataxia.

OBJECTIVE: To determine the natural history of contrast acuity in Friedreich ataxia. METHODS: In the Friedreich Ataxia-Clinical Outcome Measures Study, participants (n = 764) underwent binocular high- and low-contrast visual acuity testing at annual study visits. Mixed-effects linear regression was used to model visual acuity as a function of time, with random intercepts and slopes to account for intraindividual correlation of repeated measurements. A time-varying covariate was used to adjust for diabetes, and interaction terms were used to assess for effect modification by GAA repeat length, disease duration, and other variables. RESULTS: Across a median of 4.4 years of follow-up, visual acuity decreased significantly at 100% contrast (-0.37 letters/y, 95% confidence interval [CI]: -0.52 to -0.21), 2.5% contrast (-0.81 letters/year, 95% CI: -0.99 to -0.65), and 1.25% contrast (-1.12 letters/y, 95% CI: -1.29 to -0.96 letters/year). There was a significant interaction between time and GAA repeat length such that the rate of decrease in visual acuity was greater for patients with higher GAA repeat lengths at 2.5% contrast (p = 0.018) and 1.25% contrast (p = 0.043) but not 100% contrast. There was no effect modification by age at onset after adjusting for GAA repeat length. CONCLUSIONS: Low-contrast visual acuity decreases linearly over time in Friedreich ataxia, and the rate of decrease is greater at higher GAA repeat lengths. Contrast sensitivity has the potential to serve as a biomarker and surrogate outcome in future studies of Friedreich ataxia.

Progression of Friedreich ataxia: quantitative characterization over 5 years.

OBJECTIVE: Friedreich ataxia (FRDA) is a progressive neurodegenerative disorder of adults and children. This study analyzed neurological outcomes and changes to identify predictors of progression and generate power calculations for clinical trials. METHODS: Eight hundred and twelve subjects in a natural history study were evaluated annually across 12 sites using the Friedreich Ataxia Rating Scale (FARS), 9-Hole Peg Test, Timed 25-Foot Walk, visual acuity tests, self-reported surveys and disability scales. Cross-sectional outcomes were assessed from recent visits, and longitudinal changes were gaged over 5 years from baseline. RESULTS: Cross-sectional outcomes correlated with measures of disease severity. Age, genetic severity (guanine-adenine-adenine [GAA] repeat length), and testing site predicted performance. Serial progression was relatively linear using FARS and composite measures of performance, while individual performance outcomes were nonlinear over time. Age strongly predicted change from baseline until removing the effects of baseline FARS scores, when GAA becomes a more important factor. Progression is fastest in younger subjects and subjects with longer GAA repeats. Improved coefficients of variation show that progression results are more reproducible over longer assessment durations. INTERPRETATION: While age predicted progression speed in simple analyses and may provide an effective way to stratify cohorts, separating the effects of age and genetic severity is difficult. Controlling for baseline severity, GAA is the major determinant of progression rate in FRDA. Clinical trials will benefit from enrollment of younger subjects, and sample size requirements will shrink with longer assessment periods. These findings should prove useful in devising gene therapy trials in the near future.

Comorbid Medical Conditions in Friedreich Ataxia: Association With Inflammatory Bowel Disease and Growth Hormone Deficiency.

Friedreich ataxia is a progressive degenerative disease with neurologic and cardiac involvement. This study characterizes comorbid medical conditions in a large cohort of patients with Friedreich ataxia. Patient diagnoses were collected in a large natural history study of 641 subjects. Prevalence of diagnoses in the cohort with Friedreich ataxia was compared with prevalence in the population without Friedreich ataxia. Ten patients (1.6%) had inflammatory bowel disease, 3.5 times more common in this cohort of individuals with Friedreich ataxia than in the general population. Four subjects were growth hormone deficient, reflecting a prevalence in Friedreich ataxia that is 28 times greater than the general population. The present study identifies specific diagnoses not traditionally associated with Friedreich ataxia that are found at higher frequency in this disease. These associations could represent coincidence, shared genetic background, or potentially interactive disease mechanisms with Friedreich ataxia.

Frataxin levels in peripheral tissue in Friedreich ataxia.

OBJECTIVE: Friedreich ataxia (FRDA) is an autosomal recessive ataxia resulting from mutations in the frataxin gene (FXN). Such mutations, usually expanded guanine-adenine-adenine (GAA) repeats, give rise to decreased levels of frataxin protein in both affected and unaffected tissues. The goal was to understand the relationship of frataxin levels in peripheral tissues to disease status. METHODS: Frataxin levels were measured in buccal cells and blood, and analyzed in relation to disease features. Site-directed mutant frataxin was also transfected into human embryonic kidney cells to model results from specific point mutations. RESULTS: There was no evidence for change in frataxin levels over time with repeated measures analysis, although linear regression analysis of cross-sectional data predicted a small increase over decades. GAA repeat length predicted frataxin levels in both tissues, and frataxin levels themselves predicted neurological ratings (accounting for age). Compound heterozygous patients for a GAA expansion and a point mutation in FXN generally had lower levels of frataxin than those homozygous for the presence of two GAA repeat expansions, though levels varied dramatically between tissues in some compound heterozygotes for point mutations. The G130V mutation led to decreased levels of frataxin in vitro as well as in vivo, while the R165C mutation produced normal immunoreactive levels of frataxin both in vitro and in vivo. Start codon mutations led to low levels of frataxin in buccal cells but preserved immunoreactive frataxin levels in blood. INTERPRETATION: The present data show that peripheral frataxin levels reflect disease features in FRDA, but emphasize the need for interpretation of such levels in the context of specific mutations.

Natural history of Huntington disease.

IMPORTANCE: Understanding the natural history of Huntington disease will inform patients and clinicians on the disease course and researchers on the design of clinical trials. OBJECTIVE: To determine the longitudinal change in clinical features among individuals with Huntington disease compared with controls. DESIGN, SETTING, AND PARTICIPANTS: Prospective, longitudinal cohort study at 44 research sites in Australia (n = 2), Canada (n =4), and the United States (n = 38). Three hundred thirty-four individuals with clinically manifest Huntington disease who had at least 3 years of annually accrued longitudinal data and 142 controls consisting of caregivers and spouses who had no genetic risk of Huntington disease. MAIN OUTCOMES AND MEASURES: Change in movement, cognition, behavior, and function as measured by the Unified Huntington's Disease Rating Scale, the Mini-Mental State Examination, and vital signs. RESULTS: Total motor score worsened by 3.0 points (95% CI, 2.5-3.4) per year and chorea worsened by 0.3 point per year (95% CI, 0.1-0.5). Cognition declined by 0.7 point (95% CI, 0.6-0.8) per year on the Mini-Mental State Examination. Behavior, as measured by the product of frequency and severity score on the Unified Huntington's Disease Rating Scale, worsened by 0.6 point per year (95% CI, 0.0-1.2). Total functional capacity declined by 0.6 point per year (95% CI, 0.5-0.7). Compared with controls, baseline body mass index was lower in those with Huntington disease (25.8 vs 28.8; P < .001), and average pulse was higher (74.2 vs 69.6 beats/min; P < .001). CONCLUSIONS AND RELEVANCE: Over 3 years, the cardinal features of Huntington disease all declined in a monotonic manner. These data quantify the natural history of the disease and may inform the design of trials aimed at reducing its burden. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00313495.

Analysis of the visual system in Friedreich ataxia.

To use optical coherence tomography (OCT) and contrast letter acuity to characterize vision loss in Friedreich ataxia (FRDA). High- and low-contrast letter acuity and neurological measures were assessed in 507 patients with FRDA. In addition, OCT was performed on 63 FRDA patients to evaluate retinal nerve fiber layer (RNFL) and macular thickness. Both OCT and acuity measures were analyzed in relation to genetic severity, neurologic function, and other disease features. High- and low-contrast letter acuity was significantly predicted by age and GAA repeat length, and highly correlated with neurological outcomes. When tested by OCT, 52.7% of eyes (n = 110) had RNFL thickness values below the fifth percentile for age-matched controls. RNFL thickness was significantly lowest for those with worse scores on the Friedreich ataxia rating scale (FARS), worse performance measure composite Z2 scores, and lower scores for high- and low-contrast acuity. In linear regression analysis, GAA repeat length and age independently predicted RNFL thickness. In a subcohort of participants, 21% of eyes from adult subjects (n = 29 eyes) had macular thickness values below the first percentile for age-matched controls, suggesting that macular abnormalities can also be present in FRDA. Low-contrast acuity and RNFL thickness capture visual and neurologic function in FRDA, and reflect genetic severity and disease progression independently. This suggests that such measures are useful markers of neurologic progression in FRDA.

Depressed mood and suicidality in individuals exposed to tetrabenazine in a large Huntington disease observational study.

BACKGROUND: Tetrabenazine, a treatment for chorea in Huntington disease, carries a boxed warning due to safety, especially related to suicidality. OBJECTIVE: To compare the frequency of depressed mood and suicidality among a closely monitored cohort of individuals with Huntington disease who were exposed and not exposed to tetrabenazine. METHODS: A longitudinal prospective study involving 1360 individuals with HD evaluated at 48 research centers in Australia, Canada, and the United States was examined for frequency of depressed mood that triggered a risk assessment, suicidal thoughts, suicide attempts, and completed suicide among individuals with prior, new, and no exposure to tetrabenazine.. Seventy-seven individuals were on tetrabenazine at study enrollment (prior exposure), 64 individuals were exposed to tetrabenazine during the study's course (new exposure), and 1219 individuals had no exposure to tetrabenazine. RESULTS: The hazard ratio for depressed mood among those with prior exposure to tetrabenazine compared to no exposure was 0.9 (95% CI, 0.5-1.6) and for those with new exposure compared to no exposure was 1.2 (95% CI, 0.8-1.9). One individual (1.3%) with prior exposure, one individual (1.6%) with new exposure, and 35 individuals (2.9%) with no exposure to tetrabenazine reported suicidal thoughts. The hazard ratio for suicidal ideation among those with prior exposure to tetrabenazine compared to no exposure was 0.5 (95% CI, 0.1-3.8) and for those with new exposure to tetrabenazine compared to no exposure was 0.6 (95% CI, 0.1-4.4). Among individuals with prior or new exposure to tetrabenazine, no suicide attempts or suicides occurred. Among those with no exposure to tetrabenazine 17 suicide attempts (1.4%) and four suicides (0.3%) occurred. CONCLUSIONS: In a large observational study with close clinical supervision, tetrabenazine treatment was not associated with an increased risk of depressed mood, suicidal ideation, suicide attempts, or suicide.

Friedreich ataxia clinical outcome measures: natural history evaluation in 410 participants.

Friedreich ataxia is an autosomal recessive neurodegenerative disorder characterized by ataxia, dysarthria, and areflexia. The authors report the progress of a large international noninterventional cohort (n = 410), tracking the natural history of disease progression using the neurologic examination-based Friedreich Ataxia Rating Scale. The authors analyzed the rate of progression with cross-sectional analysis and longitudinal analysis over a 2-year period. The Friedreich Ataxia Rating Scale captured disease progression when used at 1 and 2 years following initial evaluation, with a lower ratio of standard deviation of change to mean change over 2 years of evaluation. However, modeling of disease progression identified substantial ceiling effects in the Friedreich Ataxia Rating Scale, suggesting this measure is most useful in subjects before maximal deficit is approached.

FXN methylation predicts expression and clinical outcome in Friedreich ataxia.

OBJECTIVE: Friedreich ataxia (FA) is the most common ataxia and results from an expanded GAA repeat in the first intron of FXN. This leads to epigenetic modifications and reduced frataxin. We investigated the relationships between genetic, epigenetic, and clinical parameters in a large case-control study of FA. METHODS: Clinical data and samples were obtained from individuals with FA during annual visits to our dedicated FA clinic. GAA expansions were evaluated by polymerase chain reaction (PCR) and restriction endonuclease digest. DNA methylation was measured using bisulfite-based EpiTYPER MassARRAY (Sequenom, San Diego, CA). FXN expression was determined using real-time reverse transcriptase PCR. Significant correlations between the different parameters were examined using the nonparametric Spearman rank correlation coefficient, as well as univariate and multivariate regression modeling. RESULTS: Characteristic DNA methylation was identified upstream and downstream of the expansion, and validated in an independent FA cohort. Univariate and multivariate analyses showed significant inverse correlations between upstream methylation and FXN expression, and variation in downstream methylation and age of onset. FXN expression also inversely correlated with the Friedreich Ataxia Rating Scale score, an indicator of disease severity. INTERPRETATION: These novel findings provide compelling evidence for the link between the GAA expansion, the DNA methylation profile, FXN expression, and clinical outcome in FA. Epigenetic profiling of FXN could be used to gain greater insight into disease onset and progression, but also as a biomarker to learn more about specific treatment responses and pharmacological mechanism(s). This work also highlights the potential for developing therapies aimed at increasing frataxin levels to treat this debilitating disease.

Use of Tetrabenazine in Huntington Disease Patients on Antidepressants or with Advanced Disease: Results from the TETRA-HD Study.

The safety and effectiveness of tetrabenazine in different sub-populations of Huntington disease (HD) is not known. In this study, we evaluated the safety of tetrabenazine in individuals on an antidepressant and its effectiveness in advanced HD. Tetrabenazine was not associated with an increased incidence of depressed mood among those taking antidepressants and was effective at reducing chorea in those with advanced HD.

The relationship between CAG repeat length and clinical progression in Huntington's disease.

The objective of this study was to examine the relationship between CAG repeat length (CAGn) and clinical progression in patients with Huntington's disease (HD). There are conflicting reports about the relationship between CAGn and clinical progression of HD. We conducted an analysis of data from the Coenzyme Q10 and Remacemide Evaluation in Huntington's Disease (CARE-HD) clinical trial. We modeled progression over 30 months on the Unified Huntington's Disease Rating Scale (UHDRS) and supplemental neuropsychological and behavioral tests using multiple linear regression. Mean subject age was 47.9 +/- 10.5 years and mean CAGn was 45.0 +/- 4.1. Multiple linear regression revealed statistically significant associations between CAGn and worsening on several motor, cognitive, and functional outcomes, but not behavioral outcomes. Many effects were clinically important; 10 additional CAG repeats were associated with an 81% increase in progression on the Independence Scale. These associations were not observed in the absence of age adjustment. Age at the time of assessment confounds the association between CAGn and progression. Adjusting for age shows that longer CAGn is associated with greater clinical progression of HD. This finding may account for the variable results from previous studies examining CAGn and progression. Adjusting for CAGn may be important for clinical trials.

Self-reported adherence versus pill count in Parkinson's disease: the NET-PD experience.

PURPOSE: To compare the Morisky medication adherence questionnaire to pill counts as measures of adherence in the NET-PD futility clinical trials. BACKGROUND: Like in other chronic diseases, non-adherence with medications occurs in Parkinson's disease (PD), although nonadherence has not been of significant concern in most PD clinical trials. The most common approach to assessment is to do a pill count at each visit. The simple, 4-question Morisky medication adherence questionnaire may provide an alternative approach to monitoring treatment adherence in PD. METHODS: Adherence data from two NET-PD Phase II clinical trials enrolling a total of 413 participants were analyzed. The association between demographic and clinical characteristics and adherence was explored. RESULTS: Ninety-percent of participants took 80% or more of the study drug. However, the Morisky medication adherence questionnaires showed 56% report high and 44% report medium adherence. Agreement between the two measures is fair (ICC = 0.40). CONCLUSIONS: Overall adherence as assessed by pill count appears high. The Morisky medication adherence questionnaire may be useful in PD clinical trials, since it is moderately correlated to pill count and may be more sensitive to nonadherence.