Impaired synaptic plasticity in mice carrying the Huntington's disease mutation.
(9/1997)
Cognitive impairment is an early symptom of Huntington's disease (HD). Mice engineered to carry the HD mutation in the endogenous huntingtin gene showed a significant reduction in long-term potentiation (LTP), a measure of synaptic plasticity often thought to be involved in memory. However, LTP could be induced in mutant slices by an 'enhanced' tetanic stimulus, implying that the LTP-producing mechanism is intact in mutant mice, but that their synapses are less able to reach the threshold for LTP induction. Mutant mice showed less post-tetanic potentiation than wild-type animals, and also showed decreased paired pulse facilitation, suggesting that excitatory synapses in HD mutant mice are impaired in their ability to sustain transmission during repetitive stimulation. We show that mutants, while normal in their ability to transmit at low frequencies, released significantly less glutamate during higher frequency synaptic activation. Thus, a reduced ability of Huntington synapses to respond to repetitive synaptic demand of even moderate frequency could result not only in a functional impairment of LTP induction, but could also serve as a substrate for the cognitive symptoms that comprise the early-stage pathology of HD. (+info)
A European pilot quality assessment scheme for molecular diagnosis of Huntington's disease.
(10/1997)
This paper reports a European pilot External Quality Assessment (EQA) scheme for the molecular diagnosis of Huntington's disease (HD). The European Molecular Genetics Quality Network (EMQN) chose HD as a relatively simple assay that allows a range of difficulty in terms of technical competence and interpretation. Fourteen centres from 12 different countries participated. The scheme organiser provided five cases together with mock clinical information. The participating laboratories were asked to complete the analyses and return the reports in English to their normal laboratory format within a fixed period. The scheme demonstrates a level of potential misdiagnosis in molecular analysis of HD as well as a wide variety in way of reporting laboratory results. Overall 9/146 (6.2%) of alleles fell outside the set limits, and the rate of misdiagnosis was 1/78 (1.3%). A closer estimate of diagnostic accuracy will require expansion of the scheme. (+info)
Self-assembly of polyglutamine-containing huntingtin fragments into amyloid-like fibrils: implications for Huntington's disease pathology.
(11/1997)
Huntington's disease is a progressive neurodegenerative disorder caused by a polyglutamine [poly(Q)] repeat expansion in the first exon of the huntingtin protein. Previously, we showed that N-terminal huntingtin peptides with poly(Q) tracts in the pathological range (51-122 glutamines), but not with poly(Q) tracts in the normal range (20 and 30 glutamines), form high molecular weight protein aggregates with a fibrillar or ribbon-like morphology, reminiscent of scrapie prion rods and beta-amyloid fibrils in Alzheimer's disease. Here we report that the formation of amyloid-like huntingtin aggregates in vitro not only depends on poly(Q) repeat length but also critically depends on protein concentration and time. Furthermore, the in vitro aggregation of huntingtin can be seeded by preformed fibrils. Together, these results suggest that amyloid fibrillogenesis in Huntington's disease, like in Alzheimer's disease, is a nucleation-dependent polymerization. (+info)
A worldwide assessment of the frequency of suicide, suicide attempts, or psychiatric hospitalization after predictive testing for Huntington disease.
(12/1997)
Prior to the implementation of predictive-testing programs for Huntington disease (HD), significant concern was raised concerning the likelihood of catastrophic events (CEs), particularly in those persons receiving an increased-risk result. We have investigated the frequency of CEs-that is, suicide, suicide attempt, and psychiatric hospitalization-after an HD predictive-testing result, through questionnaires sent to predictive-testing centers worldwide. A total of 44 persons (0.97%) in a cohort of 4,527 test participants had a CE: 5 successful suicides, 21 suicide attempts, and 18 hospitalizations for psychiatric reasons. All persons committing suicide had signs of HD, whereas 11 (52.4%) of 21 persons attempting suicide and 8 (44.4%) of 18 who had a psychiatric hospitalization were symptomatic. A total of 11 (84.6%) of 13 asymptomatic persons who experienced a CE during the first year after HD predictive testing received an increased-risk result. Factors associated with an increased risk of a CE included (a) a psychiatric history +info)
Huntington's disease and alcohol abuse.
(13/1997)
The dopamine, glutamate and GABA systems are known to mediate the effects of alcohol on the movement disorders, though their exact roles are not clear. Thus, use of alcohol has implications for pathogenesis as well as management of the movement disorders. These implications are discussed citing a patient who had a strong family history of Huntington's disease and in whom movement disorder and behavioral problems were manifest under alcohol use and withdrawal, but not while being abstinent. (+info)
Ultrastructural localization and progressive formation of neuropil aggregates in Huntington's disease transgenic mice.
(14/1997)
How aggregates of polyglutamine proteins are involved in the neurological symptoms of glutamine repeat diseases is unknown. We show that huntingtin aggregates are present in the neuronal processes of transgenic mice that express exon 1 of the Huntington's disease (HD) gene. Unlike aggregates in the nucleus, these neuropil aggregates are usually smaller and are not ubiquitinated. Electron microscopy reveals many neuropil aggregates in axons and axon terminals. Huntingtin aggregates in the axon terminal are co-localized with some synaptic vesicles, implying that they may affect synaptic transmission and neuronal communication. The formation of neuropil aggregates is highly correlated with the development of neurological symptoms. The present study raises the possibility that neuropil aggregates may cause a dysfunction in neuronal communication and con-tribute to the neurological symptoms of HD. (+info)
Transglutaminase aggregates huntingtin into nonamyloidogenic polymers, and its enzymatic activity increases in Huntington's disease brain nuclei.
(15/1997)
The protein huntingtin (htt), aggregated in neuronal nuclear inclusions, is pathognomonic of Huntington's disease (HD). Constructs, translated in vitro from the N terminus of htt, containing either polyQ23 from a normal individual, or polyQ41 or polyQ67 from an HD patient, were all soluble. Transglutaminase (TGase) crosslinked these proteins, and the aggregations did not have the staining properties of amyloid. More TGase-catalyzed aggregates formed when the polyglutamine domain of htt exceeded the pathologic threshold of polyQ36. Furthermore, shorter htt constructs, containing 135 aa or fewer, formed more aggregates than did larger htt constructs. TGase activity in the HD brain was increased compared with the control, with notable increases in cell nuclei. The increased TGase activity was brain specific. In lymphoblastoid cells from HD patients, TGase activity was decreased. TGase-mediated crosslinking of htt may be involved in the formation of the nonamyloidogenic nuclear inclusions found in the HD brain. The staining properties of nuclear inclusions in the HD brain revealed that they were not amyloid. (+info)
Analysis of the CAG repeat number in a patient with Huntington's disease.
(16/1997)
This study was performed to confirm 1) the difference in the trinucleotide CAG repeat number among tissues, 2) somatic mosaicism in each tissue, 3) the correlation of the repeat number with pathological severity in Huntington's disease. The CAG repeat number was determined by analysis of the polymerase chain reaction (PCR) product in various tissues, including central nervous system (CNS) tissues and non-CNS tissues. We also determined the pathological severity grade in each brain section and compared this with the results of CAG repeat analyses. The patient was a Japanese male with Huntington's disease who died at 62 years of age. Genomic DNA was extracted from 10 parts of the central nervous system and 6 parts of other tissues from the patient. Each part of the formalin-fixed brain was subjected to gross and microscopic pathological assessment. The main peaks of CAG repeat in all tissues were 22 and 44. In analysis of somatic mosaicism, high degrees of mosaicism were obtained in the caudate nucleus, putamen and cerebral cortex, in which more severe degeneration was observed by pathological examination. These results, although this is a single case study, indicated that pathological severity did not correlate with the CAG repeat number, but it did relate to the degree of somatic mosaicism. Somatic mosaicism might reflect region-specific neuronal degeneration in Huntington's disease. (+info)