Identification and allele-specific silencing of the mutant huntingtin allele in Huntington's disease patient-derived fibroblasts

Huntington's disease (HD) is a dominantly inherited neurodegenerative disorder caused by the expression of mutant huntingtin protein (Htt). Suppression of Htt expression, using RNA interference, might be an effective therapy. However, if reduction of wild-type protein is not well tolerated in the brain, it may be necessary to suppress just the product of the mutant allele. We present a small interfering RNA (siRNA) that selectively reduces the endogenous mRNA for a heterozygous HD donor's pathogenic allele by approximately 80% by specifically targeting a single-nucleotide polymorphism (SNP) located several thousand bases downstream from the disease-causing mutation. In addition, we show selective suppression of endogenous mutant Htt protein, using this siRNA. We further present a method, using just a heterozygous patient's own mRNA, to determine which SNP variants correspond to the mutant allele. The method may be useful in any disorder in which a targeted SNP is far downstream from the pathogenic mutation. These results indicate that allele-specific treatment for Huntington's disease may be clinically feasible and practical.

Creatine-supplemented diet extends Purkinje cell survival in spinocerebellar ataxia type 1 transgenic mice but does not prevent the ataxic phenotype

It is not known why expression of a protein with an expanded polyglutamine region is pathogenic in spinocerebellar ataxia, Huntington's disease and several other neurodegenerative diseases. Dietary supplementation with creatine improves survival and motor performance and delays neuronal atrophy in the R6/2 transgenic mouse model of Huntington's disease. These effects may be due to improved energy and calcium homeostasis, enhanced presynaptic glutamate uptake, or protection of mitochondria from the mitochondrial permeability transition. We tested the effects of a 2% creatine-supplemented diet and treatment with taurine-conjugated ursodeoxycholic acid, a bile constituent that can inhibit the mitochondrial permeability transition, on ataxia and Purkinje cell survival in a transgenic model of spinocerebellar ataxia type 1. After 24 weeks, transgenic mice on the 2% creatine diet had cerebellar phosphocreatine levels that were 72.5% of wildtype controls, compared to 26.8% in transgenic mice fed a control diet. The creatine diet resulted in maintenance of Purkinje cell numbers in these transgenic mice at levels comparable to wildtype controls, while transgenic mice fed a control diet lost over 25% of their Purkinje cell population. Nevertheless, the ataxic phenotype was neither improved nor delayed. Repeated s.c. ursodeoxycholic acid injections markedly elevated ursodeoxycholic acid levels in the brain without adverse effects, but provided no improvement in phenotype or cell survival in spinocerebellar ataxia type 1 mice. These results demonstrate that preserving neurons from degeneration is insufficient to prevent a behavioral phenotype in this transgenic model of polyglutamine disease. In addition, we suggest that the means by which creatine mitigates against the neurodegenerative effects of an ataxin-1 protein containing an expanded polyglutamine region is through mechanisms other than stabilization of mitochondrial membranes.

Distribution of patients' paroxysmal atrial tachyarrhythmia episodes: implications for detection of treatment efficacy

INTRODUCTION

Clinical trials of treatments for paroxysmal atrial tachyarrhythmia (pAT) often compare different treatment groups using the time to first episode recurrence. This approach assumes that the time to the first recurrence is representative of all times between successive episodes in a given patient. We subjected this assumption to an empiric test.

METHODS AND RESULTS

Records of pAT onsets from a chronologic series of 134 patients with dual chamber implantable defibrillators were analyzed; 14 had experienced >10 pAT episodes, which is sufficient for meaningful statistical modeling of the time intervals between episodes. Episodes were independent and randomly distributed in 9 of 14 patients, but a fit of the data to an exponential distribution, required by the stated assumption, was rejected in 13 of 14. In contrast, a Weibull distribution yielded an adequate goodness of fit in 5 of the 9 cases with independent and randomly distributed data. Monte Carlo methods were used to determine the impact of violations of the exponential distribution assumption on clinical trials using time from cardioversion to first episode recurrence as the dependent measure. In a parallel groups design, substantial loss of power occurs with sample sizes <500 patients per group. In a cross-over design, there is insufficient power to detect a 30% reduction in episode frequency even with 300 patients.

CONCLUSION

Clinical trials that rely on time to first episode recurrence may be considerably less able to detect efficacious treatments than may have been supposed. Analysis of multiple episode onsets recorded over time should be used to avoid this pitfall.

In vivo transduction of cerebellar Purkinje cells using adeno-associated virus vectors

We investigated whether adenovirus or adeno-associated virus vectors can transduce cerebellar Purkinje cells (PCs) in vivo. Mice were injected in the deep cerebellar nuclei (DCN) with lacZ-transducing adenovirus (Ad.RSV-betagal) or a recombinant AAV serotype 2 (rAAV2) vector (vTR-CMVbeta) mixed with wild-type adenovirus type 5 (Ad5). One week later, Ad.RSV-betagal transduced cells were found throughout the cerebellar white matter in a dose-dependent manner, but few transduced PCs were evident. In contrast, vTR-CMVbeta with Ad5 transduced several hundred PCs throughout the injected hemisphere. Using an rAAV2 vector transducing a CMV-regulated green fluorescent protein gene, we again found PC transduction, but only with Ad5 coinjection. To assess the effect of injection site and to determine whether the apparent requirement for Ad5 coinfection is observed with other promoters, a beta-actin-regulated vector was injected with or without Ad5 to DCN or cerebellar cortical sites. Thousands of transduced PCs were observed under each condition. Cortical injection yielded greater numbers of transduced cells. Injection of rAAV2 without Ad5 led to greater specificity for PC transduction. We conclude that injection of rAAV2 vectors into the cerebellum is an effective means for transferring genes into substantial numbers of Purkinje cells in vivo.

Cerebellar allografts survive and transiently alleviate ataxia in a transgenic model of spinocerebellar ataxia type-1

Spinocerebellar ataxia type 1 (SCA-1) is one of several neurodegenerative diseases, including Huntington's disease, spinobulbar muscular atrophy, dentatorubral-pallidoluysian atrophy, and SCA-2, SCA-3, SCA-6, and SCA-7, each caused by an expanded number of CAG repeats in the coding region of their respective genes. The mechanism by which the resulting proteins are pathogenic is unknown. Clinical trials of neural transplants in Huntington's disease patients are under way. While initial reports are encouraging, definitive evidence of graft survival in patients despite the ongoing disease process is not possible with current imaging techniques. Transplants in primates have shown long-term survival of striatal grafts and recovery of function, but have used lesioning to model Huntington's phenotypically. Studies of striatal grafts in a transgenic mouse model of Huntington's have not yet shown a behavioral benefit. We describe a behavioral benefit of cerebellar grafts in a transgenic model of SCA-1 in which the ataxic phenotype results from expression of an expanded ataxin-1 protein. Mice were transplanted at an age when their ataxic phenotype is just becoming evident. Compared with sham-operated littermates, grafted mice showed better performance on multiple behavioral tests of cerebellar function. Differences persisted for 10 to 12 weeks posttransplant, after which there was a progressive decline in motor performance. At 20 weeks postsurgery, donor Purkinje cell survival was evident in 9 of 12 graft recipients. These results indicate that transplants can have behavioral benefits and grafts can survive long-term despite the ongoing pathological process in a brain actively expressing an expanded polyglutamine protein.

Factors of the Rotter Internal-External scale

Previous investigators have reported that the Rotter I-E scale (1966) may measure many dimensions rather than a unidimensional trait. Following Collins (1974), each of the 23 forced-choice internal and external alternatives of the I-E scale were separated and administered as 46 Likert-scale items. The Likert-format administration was equivalent to the original method. Principal factors analysis and varimax rotation yielded five factors: belief in a nonrational world, belief in a politically unresponsive world, belief in a predictable world, belief in a just world, and belief in the meaningfulness of personal effort. These factors are similar to those reported by Collins.