Interaction of normal and expanded CAG repeat sizes influences age at onset of Huntington disease

Huntington disease (HD) is a neurodegenerative disorder caused by the abnormal expansion of CAG repeats in the HD gene on chromosome 4p16.3. Past studies have shown that the size of expanded CAG repeat is inversely associated with age at onset (AO) of HD. It is not known whether the normal Huntington allele size influences the relation between the expanded repeat and AO of HD. Data collected from two independent cohorts were used to test the hypothesis that the unexpanded CAG repeat interacts with the expanded CAG repeat to influence AO of HD. In the New England Huntington Disease Center Without Walls (NEHD) cohort of 221 HD affected persons and in the HD-MAPS cohort of 533 HD affected persons, we found evidence supporting an interaction between the expanded and unexpanded CAG repeat sizes which influences AO of HD (P = 0.08 and 0.07, respectively). The association was statistically significant when both cohorts were combined (P = 0.012). The estimated heritability of the AO residual was 0.56 after adjustment for normal and expanded repeats and their interaction. An analysis of tertiles of repeats sizes revealed that the effect of the normal allele is seen among persons with large HD repeat sizes (47-83). These findings suggest that an increase in the size of the normal repeat may mitigate the expression of the disease among HD affected persons with large expanded CAG repeats.

Weight loss in early stage of Huntington's disease

BACKGROUND

Huntington's disease (HD) is an autosomal dominant disease with neurologic manifestations. In transgenic mouse models of HD, weight loss is recognized as a feature associated with the disease onset. It is unclear whether a similar pattern occurs in humans.

METHODS

Data from the Huntington Study Group were used to evaluate whether HD is associated with lower body mass index (BMI) at the earliest stage of the disease. There were 361 case subjects in whom HD had been diagnosed with an independence scale rating of 100 (no special care needed), a total functional capacity score of >or=11, and HD duration of <4 years. For each case subject, five sex- and age-matched control subjects were selected from the National Heart, Lung, and Blood Institute Family Heart Study or the Framingham Offspring Study.

RESULTS

Among case subjects, neither disease duration, nor dystonia, nor chorea score was significantly associated with BMI. BMI was significantly lower among case than among control subjects. Among men, age-adjusted BMI (+/-SE) was 25.90 +/- 0.34 kg/m(2) for case subjects with HD and 27.68 +/- 0.16 kg/m(2) for control subjects. Among women, corresponding values were 24.34 +/- 0.43 for case subjects with HD and 26.63 +/- 0.21 kg/m(2) for control subjects.

CONCLUSIONS

At an early stage of the disease, subjects with Huntington's disease had lower body mass index than matched controls from the general population. The cause of weight loss is unknown but the parallel to observations in Huntington's disease transgenic mice suggests that it is a significant hallmark of Huntington's disease gene expression.

Effects of paired and unpaired eye-blink conditioning on Purkinje cell morphology

This experiment addressed (1) the importance of conjunctive stimulus presentation for morphological plasticity of cerebellar Purkinje cells and inhibitory interneurons and (2) whether plasticity is restricted to the spiny branches of Purkinje cells, which receive parallel fiber input. These issues were investigated in naive rabbits and in rabbits that received paired or unpaired presentations of the conditioned stimulus (CS) and unconditioned stimulus (US). To direct CS input to the cerebellar cortex, pontine stimulation served as the CS. Air puffs to the cornea served as the US. Paired condition rabbits received pontine stimulation for 350 msec paired with a coterminating 100-msec air puff. Unpaired condition rabbits received the same stimuli in a pseudorandom order at 1- to 32-sec intervals. Rabbits were trained for a mean of 12 days. Naive rabbits received no treatment. In Golgi-stained Purkinje neurons in lobule HVI, total dendritic length, main branch length, total spiny branch length, and number of spiny branch arbors were all greater in the naive group than in the paired and unpaired groups, which did not differ. No differences were found between the hemispheres ipsilateral and contralateral to the trained eye. The dendritic length and number of branches for inhibitory interneurons did not differ across groups. The Purkinje cell morphological changes detected with these methods do not appear to be uniquely related to the conjunctive activation of the CS and US in the paired condition.

Effect of nootropic Solcoseryl on kainic acid-induced excitotoxic brain injury

Solcoseryl (S) has been shown to provide significant cytoprotection in a variety of models of cerebral hypoxia. In the present study, we quantified the epileptiform effects caused by kainic acid administered into the pontine reticular formation of rats and their response to S pretreatment. Compared to saline, the agent appeared to significantly reduce the mortality of rats in the course of status epilepticus. However, S-pretreated rats manifested an increased incidence of behavioral seizures. This untoward effect is attributed to the fact that S improves the functional potential of injured tissue and retards the period of metabolic exhaustion at a time when neuronal activity should be minimized.

Hippocampal stimulation disrupts spatial working memory even 8 h after acquisition

The present experiment used hippocampal stimulation to determine the temporal gradient of consolidation of spatial working memory. Rats were trained to perform a spatial working memory task on a radial maze with 12 arms. Each rat went to the ends of 6 arms to obtain a food reward. After 8 h, the rat chose among all the arms to find the ones not previously chosen (and consequently still having food). During some test sessions, the hippocampus was stimulated electrically either at a current level just high enough to produce an electrophysiological seizure, or at a current level below this seizure threshold. Stimulation occurred at one of five intervals (0 to 8 h) following the completion of the first six choices. During other test sessions, the hippocampus was not stimulated. After seizure stimulation, the number of retroactive errors (returning to arms chosen prior to stimulation) increased at all delay intervals; the number of proactive errors (returning to arms chosen after stimulation) increased only with the delay of 8 h. Subthreshold stimulation had no influence on either type of error. These results indicate that normal hippocampal function is required for the maintenance of spatial information in working memory, and that the time course of consolidation of this information is significantly greater than that seen in other types of memory, or consolidation may not take place at all.