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Perhaps as many as 25-50% of adult patients and children with acquired immunodeficiency syndrome (AIDS) eventually suffer from neurological manifestations, including dysfunction of cognition, movement, and sensation. How can human immunodeficiency virus type 1 (HIV-1) result in neuronal damage if neurons themselves are for all intents and purposes not infected by the virus? This article reviews a series of experiments leading to a hypothesis that accounts at least in part for the neurotoxicity observed in the brains of AIDS patients. There is growing support for the existence of HIV- or immune-related toxins that lead indirectly to the injury or demise of neurons via a potentially complex web of interactions among macrophages (or microglia), astrocytes, and neurons. HIV-infected monocytoid cells (macrophages, microglia, or monocytes), after interacting with astrocytes, secrete eicosanoids, i.e., arachidonic acid and its metabolites, including platelet-activating factor. Macrophages activated by HIV-1 envelope protein gp120 also appear to release arachidonic acid and its metabolites. In addition, interferon-gamma (IFN-gamma) stimulation of macrophages induces release of the glutamate-like agonist, quinolinate. Furthermore, HIV-infected macrophage production of cytokines, including TNF-alpha and IL1-beta, contributes to astrogliosis. A final common pathway for neuronal susceptibility appears to be operative, similar to that observed in stroke, trauma, epilepsy, neuropathic pain, and several neurodegenerative diseases, possibly including Huntington's disease, Parkinson's disease, and amyotrophic lateral sclerosis. This mechanism involves the activation of voltage-dependent Ca2+ channels and N-methyl-D-aspartate (NMDA) receptor-operated channels, and, therefore, offers hope for future pharmacological intervention. This article focuses on clinically tolerated calcium channel antagonists and NMDA antagonists with the potential for trials in humans with AIDS dementia in the near future.
Mol Neurobiol
PMID:HIV-related neuronal injury. Potential therapeutic intervention with calcium channel antagonists and NMDA antagonists. 799 15

The incurable neurodegenerative disorder, Huntington's disease (HD), is caused by an expanded, unstable CAG repeat encoding a stretch of polyglutamine in a 4p16.3 gene (HD) of unknown function. Near the CAG repeat is a polyproline-encoding CCG repeat that shows more limited allelic variation. The mouse homologue, Hdh, has been mapped to chromosome 5, in a region devoid of mutations causing any comparable phenotype. We have isolated overlapping cDNAs from the Hdh gene and compared their sequences with the human transcript. The consensus mouse coding sequence is 86% identical to the human at the DNA level and 91% identical at the protein level. Despite the overall high level of conservation, Hdh possesses an imperfect CAG repeat encoding only seven consecutive glutamines, compared to the 13-36 residues that are normal in man. Although no evidence for polymorphic variation of the CAG repeat was seen, a nearby CCG repeat differed in length by one unit between several strains of laboratory mouse and Mus spretus. The absence of a long CAG repeat in the mouse is consistent with the lack of a spontaneous mouse model of HD. The information presented concerning the sequence of the mouse gene should facilitate attempts to create such a model.
Somat Cell Mol Genet 1994 Mar
PMID:Mouse Huntington's disease gene homolog (Hdh). 800 70

The gene causing Huntington's disease, an autosomal dominantly inherited, neurodegenerative disorder, has been identified recently. The corresponding mutation is involving an expansion in the number of (CAG)n repeats in the coding region of the Huntington's disease gene on chromosome 4. In this report, we demonstrate the length variation of the repeat in 513 non-HD chromosomes from normal individuals and HD patients showing 23 alleles with 11 to 33 repeats. Analyzing the inheritance of the (CAG)n stretch we found meiotic instability for HD alleles ([CAG]40 to [CAG]75) with a mutation frequency of approximately 0.7, while in 431 meioses of normal alleles only two expansions were identified. The risk of expansion during spermatogenesis is enhanced compared to oogenesis explaining juvenile onset by transmission from affected fathers. Further, the number of (CAG)n copies in an affected individual in relation to the sex of the transmitting parent was evaluated and no significant differences were found. No mosaicism or differences in the repeat lengths were observed in the DNA from different tissues including brain and lymphocytes of two HD patients indicating mitotic stability of the mutation. Therefore, the determination of the repeat number in the DNA of blood lymphocytes is probably representative of all tissues in a patient.
Hum Mol Genet 1993 Dec
PMID:Mitotic stability and meiotic variability of the (CAG)n repeat in the Huntington disease gene. 811 74

The recent identification of the Huntington's disease (HD) gene, enabled us to synthesize oligopeptides corresponding with the carboxy-terminal end of the predicted HD-gene (IT15) product. Immunobiochemcial studies with polyclonal antibodies directed against this synthetic peptide (position 3114-3141) on lymphoblastoid cells from normal individuals and patients with Huntington disease, revealed the presence of a protein (huntingtin) with a molecular mass of approximately 330 kDa. Immunocytochemical studies showed a cytoplasmic localization of huntingtin in various cell types including neurons. In most of the neuronal cells the protein was also present in the nucleus. No difference in molecular mass or intracellular localization was found between normal and mutant cells.
Hum Mol Genet 1993 Dec
PMID:Characterization and localization of the Huntington disease gene product. 811 75

The CCG rich sequence immediately 3' to the CAG repeat that is expanded in Huntington's disease (HD) has recently been shown to be polymorphic with at least 4 alleles differing by multiples of 3 bp being found in the normal population. We have studied the allele distribution in 180 HD families resident in Scotland and have found very strong evidence for disequilibrium in this population. For the 131 families where phase was unambiguously determined, 130 were shown to have a CCG repeat allele of 176 bp cosegregating with the HD chromosome. This observation is significantly different to the normal population distribution where 31% of people have an allele of 185 bp. The evidence for and against a possible founder effect in the Scottish HD population is discussed. We propose the hypothesis that we may have identified a region of the IT15 gene that is critical in Huntington's disease.
Hum Mol Genet 1994 Jan
PMID:A single allele from the polymorphic CCG rich sequence immediately 3' to the unstable CAG trinucleotide in the IT15 cDNA shows almost complete disequilibrium with Huntington's disease chromosomes in the Scottish population. 816 20

The polymorphic CAG repeat that is expanded on Huntington disease (HD) chromosomes is flanked by a CCG repeat. Here we show that this CCG tract, previously assumed to be invariant at seven CCG repeats, is also polymorphic. We have identified five CCG alleles from 205 normal chromosomes, with 137 (67%) having alleles of seven repeats, five (2%) with nine repeats, 61 (30%) with 10 repeats, one (0.5%) with 11 repeats and one (0.5%) with 12 repeats. In contrast, analysis of 113 HD chromosomes revealed that the majority (105 chromosomes, 93%) contained seven CCG repeats, while the remaining eight chromosomes (7%) had allele sizes of 10 CCG repeats. Despite evidence that both CAG and CCG are polymorphic on normal chromosomes, we have found that it is only the CAG length that has a significant impact on age of onset. The discovery of larger sized CCG alleles, however, has significant implications for the assessment of CAG repeat length, particularly for persons with estimated CAG size of 36-42 repeats, since an overestimation of CAG length in this range could result in erroneous information being imparted to patients.
Hum Mol Genet 1994 Jan
PMID:A CCG repeat polymorphism adjacent to the CAG repeat in the Huntington disease gene: implications for diagnostic accuracy and predictive testing. 816 53

The recent observation that the mutation underlying a number of genetic diseases including fragile sites, FRAXA and FRAXE (associated with mental retardation), myotonic dystrophy, spinal and bulbar muscular atrophy (Kennedy's disease), Huntington's disease and spinocerebellar ataxia type 1 are caused by the expansion of a trinucleotide repeat sequence will lead to interest in the identification of such sequences in regions related to other diseases. We report here the identification of all ten classes of trinucleotide repeats within a 2 Mbp region of 4p16.3 containing the Huntington's disease (HD) gene. Fifty one triplet repeats were identified and localised on a high resolution restriction map of a cosmid contig covering this region. This included the triplet repeat (CAG)n, which has subsequently been shown to be expanded in Huntington's disease patients.
Hum Mol Genet 1994 Jan
PMID:Distribution of trinucleotide repeat sequences across a 2 Mbp region containing the Huntington's disease gene. 816 55

Huntington disease (HD) is associated with significant expansion of a CAG trinucleotide repeat within a novel gene. However, no clues to the function of this gene were apparent by sequence alignment to other proteins. We have therefore sought to identify the mouse gene (hd) as a first step in the development of an animal model for HD to provide insights into the molecular pathogenesis of this disease. Here, we report the sequencing of cDNA clones spanning 9,992 nucleotides encoding the murine HD homologue (hd), which exhibits 90% peptide sequence identity, including conservation of the CAG and adjacent CCG repeats. In addition, we show that the CCG is polymorphic in the mouse. Sequence analysis provides strong evidence that the first in frame methionine 5' to the CAG repeat, is the translational start site, for both the mouse and human transcript. As in human, the gene appears expressed in the mouse as 2 large transcripts. We observe evidence for alternate splicing of the hd gene in mouse tissues which would predict two protein products differing by 480 amino acid residues with a molecular mass difference of approximately 54 kilodaltons.
Hum Mol Genet 1994 Jan
PMID:Sequence of the murine Huntington disease gene: evidence for conservation, alternate splicing and polymorphism in a triplet (CCG) repeat [corrected]. 816 57

Huntington's disease, a neurodegenerative disorder characterized by loss of striatal neurons, is caused by an expanded, unstable trinucleotide repeat in a novel 4p16.3 gene. To lay the foundation for exploring the pathogenic mechanism in HD, we have determined the structure of the disease gene and examined its expression. The HD locus spans 180 kb and consists of 67 exons ranging in size from 48 bp to 341 bp with an average of 138 bp. Scanning of the HD transcript failed to reveal any additional sequence alterations characteristic of HD chromosomes. A codon loss polymorphism in linkage disequilibrium with the disorder revealed that both normal and HD alleles are represented in the mRNA population in HD heterozygotes, indicating that the defect does not eliminate transcription. The gene is ubiquitously expressed as two alternatively polyadenylated forms displaying different relative abundance in various fetal and adult tissues, suggesting the operation of interacting factors in determining specificity of cell loss. The HD gene was disrupted in a female carrying a balanced translocation with a breakpoint between exons 40 and 41. The absence of any abnormal phenotype in this individual argues against simple inactivation of the gene as the mechanism by which the expanded trinucleotide repeat causes HD. Taken together, these observations suggest that the dominant HD mutation either confers a new property on the mRNA or, more likely, alters an interaction at the protein level.
Somat Cell Mol Genet 1994 01
PMID:Structure and expression of the Huntington's disease gene: evidence against simple inactivation due to an expanded CAG repeat. 819 74

IT15 is a novel gene, localized to chromosome 4, and encoding a protein named Huntingtin. A polymorphic CAG repeat in the proposed open reading frame of IT15 has been characterized, and an elongation of this repeat has been correlated to Huntington's Disease. We have investigated the CAG repeat in the Huntingtin gene in 71 unrelated Danish patients with Huntington's Disease, and found repeat lengths of 39 to 70 repeat units in contrast to 9 to 30 CAG's on normal chromosomes. Comparison of repeat length and age at onset of disease symptoms in 52 individuals indicates an inverse correlation between the age at onset and the number of CAG repeat units.
Hum Mol Genet 1993 Sep
PMID:Trinucleotide repeat elongation in the Huntingtin gene in Huntington disease patients from 71 Danish families. 824 74


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