Intermediate repeat expansions of TBP and STUB1: Genetic modifier or pure digenic inheritance in spinocerebellar ataxias?

PURPOSE: CAG/CAA repeat expansions in TBP>49 are responsible for spinocerebellar ataxia (SCA) type 17 (SCA17). We previously detected cosegregation of STUB1 variants causing SCA48 with intermediate alleles of TBP in 2 families. This cosegregation questions the existence of SCA48 as a monogenic disease. METHODS: We systematically sequenced TBP repeats in 34 probands of dominant ataxia families with STUB1 variants. In addition, we searched for pathogenic STUB1 variants in probands with expanded alleles of TBP>49 (n = 2) or intermediate alleles of TBP≥40 (n = 47). RESULTS: STUB1 variants were found in half of the TBP40-49 cohort. Mirroring this finding, TBP40-49 alleles were detected in 40% of STUB1 probands. The longer the TBP repeat length, the more likely the occurrence of cognitive impairment (P = .0129) and the faster the disease progression until death (P = .0003). Importantly, 13 STUB1 probands presenting with the full SCA48 clinical phenotype had normal TBP37-39 alleles, excluding digenic inheritance as the sole mode. CONCLUSION: We show that intermediate TBP40-49 alleles act as disease modifiers of SCA48 rather than a STUB1/TBP digenic model. This distinction from what has been proposed before has crucial consequences for genetic counseling in SCA48.

Dynamic Imaging of Individual Remyelination Profiles in Multiple Sclerosis.

BACKGROUND: Quantitative in vivo imaging of myelin loss and repair in patients with multiple sclerosis (MS) is essential to understand the pathogenesis of the disease and to evaluate promyelinating therapies. Selectively binding myelin in the central nervous system white matter, Pittsburgh compound B ([11 C]PiB) can be used as a positron emission tomography (PET) tracer to explore myelin dynamics in MS. METHODS: Patients with active relapsing-remitting MS (n = 20) and healthy controls (n = 8) were included in a longitudinal trial combining PET with [11 C]PiB and magnetic resonance imaging. Voxel-wise maps of [11 C]PiB distribution volume ratio, reflecting myelin content, were derived. Three dynamic indices were calculated for each patient: the global index of myelin content change; the index of demyelination; and the index of remyelination. RESULTS: At baseline, there was a progressive reduction in [11 C]PiB binding from the normal-appearing white matter to MS lesions, reflecting a decline in myelin content. White matter lesions were characterized by a centripetal decrease in the tracer binding at the voxel level. During follow-up, high between-patient variability was found for all indices of myelin content change. Dynamic remyelination was inversely correlated with clinical disability (p = 0.006 and beta-coefficient = -0.67 with the Expanded Disability Status Scale; p = 0.003 and beta-coefficient = -0.68 with the MS Severity Scale), whereas no significant clinical correlation was found for the demyelination index. INTERPRETATION: [11 C]PiB PET allows quantification of myelin dynamics in MS and enables stratification of patients depending on their individual remyelination potential, which significantly correlates with clinical disability. This technique should be considered to assess novel promyelinating drugs. Ann Neurol 2016;79:726-738.

A diagnostic flow chart for POLG-related diseases based on signs sensitivity and specificity.

OBJECTIVE: Diseases due to mutations of POLG gene, encoding the mitochondrial DNA polymerase, are reputed to have very diverse clinical presentations and have been proposed to cause up to 25% adult mitochondrial diseases. Our objective was the evaluation of the specificity and sensitivity of the signs encountered with POLG mutations. DESIGN: Forty-four patients out of 154 with sequenced POLG gene had mutations affecting either one (POLG(+/-) group) or two POLG alleles (POLG(+/+) group). Phenotyping included clinical signs, electroneuromyography and brain imaging while mitochondrial investigations encompassed muscle histochemistry, respiratory chain assays and search for multiple mitochondrial deletions. The specificity and sensitivity of the signs associated with POLG mutations were analysed by comparison between POLG(+/+) and patients without POLG mutation. RESULTS: High sensitivity but low specificity was observed with single signs such as axonal sensory neuropathy, cerebellar syndrome, movement disorders and weakness involving ocular, pharyngeal, axial and/or limb muscles. Specificity was increased with combination of previous signs plus psychiatric symptoms, cognitive impairment and epilepsy. High specificity and sensitivity was only obtained with sensory neuronopathy associated with one of the following signs: weakness of ocular, pharyngeal, axial and/or limb muscles. Mitochondrial investigations did not suffice for diagnosis. The widespread neuromuscular signs were often present since disease onset and were the rule above 50 years of age leading to a very low probability of POLG mutations in patients with less than three signs and absent sensory neuropathy. CONCLUSIONS: Phenotypes associated with POLG mutations follow a reproducible pattern, which allows establishing a diagnostic flow chart.

Clinical and genetic keys to cerebellar ataxia due to FGF14 GAA expansions.

BACKGROUND: SCA27B caused by FGF14 intronic heterozygous GAA expansions with at least 250 repeats accounts for 10-60% of cases with unresolved cerebellar ataxia. We aimed to assess the size and frequency of FGF14 expanded alleles in individuals with cerebellar ataxia as compared with controls and to characterize genetic and clinical variability. METHODS: We sized this repeat in 1876 individuals from France sampled for research purposes in this cross-sectional study: 845 index cases with cerebellar ataxia and 324 affected relatives, 475 controls, as well as 119 cases with spastic paraplegia, and 113 with familial essential tremor. FINDINGS: A higher frequency of expanded allele carriers in index cases with ataxia was significant only above 300 GAA repeats (10.1%, n = 85) compared with controls (1.1%, n = 5) (p < 0.0001) whereas GAA250-299 alleles were detected in 1.7% of both groups. Eight of 14 index cases with GAA250-299 repeats had other causal pathogenic variants (4/14) and/or discordance of co-segregation (5/14), arguing against GAA causality. We compared the clinical signs in 127 GAA≥300 carriers to cases with non-expanded GAA ataxia resulting in defining a key phenotype triad: onset after 45 years, downbeat nystagmus, episodic ataxic features including diplopia; and a frequent absence of dysarthria. All maternally transmitted alleles above 100 GAA were unstable with a median expansion of +18 repeats per generation (r2 = 0.44; p < 0.0001). In comparison, paternally transmitted alleles above 100 GAA mostly decreased in size (-15 GAA (r2 = 0.63; p < 0.0001)), resulting in the transmission bias observed in SCA27B pedigrees. INTERPRETATION: SCA27B diagnosis must consider both the phenotype and GAA expansion size. In carriers of GAA250-299 repeats, the absence of documented familial transmission and a presentation deviating from the key SCA27B phenotype, should prompt the search for an alternative cause. Affected fathers have a reduced risk of having affected children, which has potential implications for genetic counseling. FUNDING: This work was supported by the Fondation pour la Recherche Médicale, grant number 13338 to JLM, the Association Connaître les Syndrome Cérébelleux - France (to GS) and by the European Union's Horizon 2020 research and innovation program under grant agreement No 779257 ("SOLVE-RD" to GS). DP holds a Fellowship award from the Canadian Institutes of Health Research (CIHR). SK received a grant (01GM1905C) from the Federal Ministry of Education and Research, Germany, through the TreatHSP network. This work was supported by the Australian Government National Health and Medical Research Council grants (GNT2001513 and MRFF2007677) to MB and PJL.

Annual change in Friedreich's ataxia evaluated by the Scale for the Assessment and Rating of Ataxia (SARA) is independent of disease severity.

BACKGROUND: The objective of the study was to evaluate the sensitivity to change of the Scale for the Assessment and Rating of Ataxia (score, 0-40) in Friedreich's ataxia. METHODS: This was a follow-up study in adult patients with genetically confirmed Friedreich's ataxia evaluated at least twice (minimum interval, 6 months). Participants were outpatients at the Center for Neurogenetics of the Pitie-Salpêtrière Hospital in Paris. RESULTS: We included 84 patients; 60% had 3 or more evaluations. The mean score on first assessment was 22.7 ± 9, and the mean follow-up was 1.84 ± 1.10 years. The mean increase was 1.36 ± 2.3 points/year; this variation was not significantly linked to factors known to influence disease severity such as age at onset, disease duration, GAA expansion length, and wheelchair use. CONCLUSIONS: In adult Friedreich's ataxia patients the Scale for the Assessment and Rating of Ataxia can detect annual changes independently of disease severity. In future therapeutic trials no patient stratification is globally required.

Quantitative assessment of the evolution of cerebellar signs in spinocerebellar ataxias.

BACKGROUND: Responsive ataxia rating scales are essential for determining outcome measures in clinical trials. METHODS: We evaluated the responsiveness over time of the composite cerebellar functional severity score, a quantitative score measuring cerebellar ataxia in 133 patients with autosomal dominant cerebellar ataxias (ADCA), which were prospectively evaluated at inclusion and after one-year of follow-up. A more responsive tool was developed, the Cerebellar Functional Severity score writing, incorporating the writing test at dominant hand to the Cerebellar Functional Severity score. RESULTS: Within the one-year follow-up period, the Cerebellar Functional Severity score and its writing version increased significantly and the Scale for the Assessment and Rating of Ataxia decreased significantly reflecting increased severity of the cerebellar symptoms. The Cerebellar Functional Severity score writing responsiveness was best in genotypes SCA1, 2, and 3 compared with the other genotypes (effect size = 0.196, standardized response mean (SRM) = 0.624 versus effect size = -0.051, SRM = -0.150). The Cerebellar Functional Severity score writing used as an outcome measure would require only 163 SCA1, 2, or 3 patients per group in a two-arm interventional trial for a 50% reduction in progression and 80% of power. DISCUSSION: Our study demonstrates that the Cerebellar Functional Severity score and Cerebellar Functional Severity score writing are responsive quantitative scores for evaluating sensitivity to change in ADCA patients and can be used as outcome measures in clinical trials, especially when targeting genotypes SCA1, 2 and 3.

Frequency of mitochondrial defects in patients with chronic intestinal pseudo-obstruction.

BACKGROUND & AIMS: Chronic intestinal pseudo-obstruction (CIPO) is a rare disorder caused by intestinal dysmotility and characterized by chronic symptoms suggesting bowel obstruction in the absence of fixed, occluding lesions. CIPO has been associated with primary defects of the mitochondrial oxidative phosphorylation pathway, although the frequency of mitochondrial disorders in patients with CIPO is unknown. This study evaluates mitochondrial function in patients with CIPO. METHODS: A retrospective study was performed of data collected from 80 CIPO patients at a tertiary centre over a 25-year period. Mitochondrial disorders were detected by analysis of serum lactate and thymidine phosphorylase activities, brain magnetic resonance images, and muscle biopsies. Genes encoding thymidine phosphorylase, mitochondrial DNA tRNA(leu(UUR)) or tRNA(lys), and DNA polymerase-gamma were analyzed for mutations. RESULTS: Mitochondrial defects were identified in 15 patients (10 women; median age at diagnosis 32 years), representing 19% of the study cohort. All 15 patients had extra-digestive symptoms, 5 had mutations in the thymidine phosphorylase gene, 2 had mutations in tRNA(leu(UUR)), and 5 had mutations in the DNA polymerase-gamma gene. No genetic defect was detected in 3 of the patients with mitochondrial disorders. Patients with mitochondrial CIPO differed from patients without mitochondrial defects in their very severe nutritional status (frequent and long-term requirement for parenteral nutrition) and poor prognosis (frequent digestive and neurologic complications that led to a high incidence of premature death). CONCLUSION: Mitochondrial disorders seem to be an important cause of CIPO. Patients with CIPO, especially severe cases with associated neurologic symptoms, should be tested for mitochondrial defects.

Quantitative neuroimaging biomarkers in a series of 20 adult patients with POLG mutations.

Mutations in the gene encoding polymerase gamma (POLG) are a common cause of mitochondrial diseases in adults. We retrospectively analyzed volumetric and diffusion tensor imaging data from 20 adult POLG-mutated patients compared to healthy controls. We used an original clinical binary load score and electroneuromyography to evaluate disease severity. Patients showed atrophy in the basal ganglia, amygdala, and brainstem (p < 0.05) compared to controls, as well as decreased fractional anisotropy (FA) in the cingulate gyrus, the internal capsule and the corona radiata (p < 0.05). Clinical scores correlated with decreased FA and increased radial diffusivity in several brain regions (p < 0.05).

Low cancer prevalence in polyglutamine expansion diseases.

OBJECTIVE: Polyglutamine (PolyQ) diseases are dominantly transmitted neurologic disorders, caused by coding and expanded CAG trinucleotide repeats. Cancer was reported retrospectively to be rare in patients with PolyQ diseases and we aimed to investigate its prevalence in France. METHODS: Consecutive patients with Huntington disease (HD) and spinocerebellar ataxia (SCA) were questioned about cancer, cardiovascular diseases, and related risk factors in 4 university hospitals in Paris, Toulouse, Strasbourg, and Montpellier. Standardized incidence ratios (SIR), based on age- and sex-adjusted rate of the French population, were assessed for different types of cancer. RESULTS: We questioned 372 patients with HD and 134 patients with SCA. SIR showed significantly reduced risk of cancer in HD: 23 observed cases vs 111.05 expected ones (SIR 0.21, 95% confidence interval [CI] 0.13-0.31), as well as in SCA: 7 observed cases vs 34.73 expected (SIR 0.23, 95% CI 0.08-0.42). This was surprising since risk behavior for cancer was increased in these patients, with significantly greater tobacco and alcohol consumption in patients with HD vs patients with SCA (p < 0.0056). There was no association between CAG repeat size and cancer or cardiovascular disease. However, in patients with HD, skin cancers were more frequent than expected (5 vs 0.98, SIR 5.11, 95% CI 1.65-11.95). CONCLUSIONS: There was a decreased cancer rate in PolyQ diseases despite high incidence of risk factors. Intriguingly, skin cancer incidence was higher, suggesting a crosstalk between neurodegeneration and skin tumorigenesis.

Nocturnal agitation in Huntington disease is caused by arousal-related abnormal movements rather than by rapid eye movement sleep behavior disorder.

BACKGROUND: Patients with Huntington disease (HD) and their spouses often complain of agitation during sleep, but the causes are mostly unknown. OBJECTIVE: To evaluate sleep and nocturnal movements in patients with various HD stages and CAG repeats length. METHODS: The clinical features and sleep studies of 29 patients with HD were retrospectively collected (11 referred for genotype-phenotype correlations and 18 for agitation during sleep) and compared with those of 29 age- and sex-matched healthy controls. All patients had videopolysomnography, but the movements during arousals were re-analyzed in six patients with HD with stored video. RESULTS: The patients had a longer total sleep period and REM sleep onset latency, but no other differences in sleep than controls. There was no correlation between CAG repeat length and sleep measures, but total sleep time and sleep efficiency were lower in the subgroup with moderate than milder form of HD. Periodic limb movements and REM sleep behavior disorders were excluded, although 2/29 patients had abnormal REM sleep without atonia. In contrast, they had clumsy and opisthotonos-like movements during arousals from non-REM or REM sleep. Some movements were violent and harmful. They might consist of voluntary movements inappropriately involving the proximal part of the limbs on a background of exaggerated hypotonia. Giant (>65 mcV) sleep spindles were observed in seven (24%) patients with HD and one control. CONCLUSION: The nocturnal agitation in patients with HD seems related to anosognostic voluntary movements on arousals, rather than to REM sleep behavior disorder and other sleep problems.

Factors influencing disease progression in autosomal dominant cerebellar ataxia and spastic paraplegia.

OBJECTIVES: To evaluate disease progression and determine validity of clinical tools for therapeutic trials. DESIGN: Prospective cohort study (36 months). SETTING: Referral center. PATIENTS: One hundred sixty-two patients with autosomal dominant cerebellar ataxia and 64 with hereditary spastic paraplegia. MAIN OUTCOME MEASURES: The quantitative Composite Cerebellar Functional Severity Score with the writing test (CCFSw) and Scale for the Assessment and Rating of Ataxia (SARA) score. RESULTS: Disease worsened in patients with SCA1, SCA2, and SCA3 mutations (mean [SE] increase in CCFSw, +0.014 [0.005] to +0.025 [0.004] per year), improved in patients with SPG4 mutations (mean [SE] increase in CCFSw, -0.012 [0.003] per year; P = .02), and remained stable in patients with SCA6, SCA7, or other SCA mutations (mean [SE] increase in CCFSw, -0.015 [0.011] to +0.009 [0.013] per year) or hereditary spastic paraplegia with other SPG mutations (mean [SE] increase in CCFSw, -0.005 [0.005] per year). Progression was faster in patients with SCA2 mutations and normal alleles with 22 or fewer repeats (P = .02) and in patients with SCA3 mutations with parkinsonism and/or dystonia at baseline (P = .003). Whereas CCFSw distinguished between patients with ataxia and spasticity, SARA scores increased in both groups. A 2-arm trial with SARA score as the outcome measure would require 57 patients with SCA2 mutations, 70 with SCA1 mutations, and 75 with SCA3 mutations per group to detect a 50% reduction in disease progression (power, 80%; α = .05). CONCLUSIONS: Disease progressed faster in SCA s with polyglutamine expansions in SCA1, 2, and 3 than the other groups. Both outcome measures are suitable for therapeutic trials; SARA requires fewer patients to attain the same power, but CCFSw needs less stratification. We demonstrate that the choice of clinical outcome measure is critical for reliable evaluation of progression in neurodegenerative diseases.