Biomedical subjects

David Comas

Publications and source records attributed to David Comas.

6 recordsLinked to original sources

PubMed2003

Association study between Alzheimer's disease and genes involved in Abeta biosynthesis, aggregation and degradation: suggestive results with BACE1.

BACKGROUND: Amyloid beta-peptide (Abeta) biosynthesis, aggregation and degradation constitute three important steps to consider in the study of pathological mechanisms involved in Alzheimer's disease (AD). Several proteins have been suggested as involved in each of these processes: proteolytic cleavage of the amyloid precursor protein by the beta-site APP cleaving enzyme (BACE), increased amyloid fibril formation by the activity of the acetylcholinesterase (ACHE gene), and degradation of Abeta aggregates by the plasmin system have been exhaustively documented. METHODS: A case-control design was used to evaluate the possible association between candidate genes involved in these three processes and AD. We analysed three polymorphisms located at the BACE1 gene, one polymorphism at the ACHE gene, and two variants located at the tissue plasminogen activator and plasminogen activator inhibitor-1 (genes TPA and PAI- 1, respectively), both part of the plasmin system. RESULTS: We found an association between BACE1 exon 5 GG genotype and AD (age-and gender-adjusted odds ratio = 2.14, P =0.014). Although a similar association was reported previously by Nowotny and collaborators only in subjects carrying the epsilon4-allele of the apolipoprotein E gene (APOE), we did not detect this effect. However,when we combined our results with those previously reported, a clear increase of the risk to develop AD appeared in subjects carrying both the BACE1 exon 5 GG genotype and the APOE epsilon4-allele (crude OR = 2.2, P = 0.004). CONCLUSION: These data suggest a possible genetic relation between BACE1 and AD.

3' Untranslated Regions↗

PubMed2003

Joint analysis of candidate genes related to Alzheimer's disease in a Spanish population.

BACKGROUND: Besides the repeated association between the epsilon 4 allele of the apolipoprotein E and Alzheimer's disease, several candidate genes have been analysed with inconsistent results. Most of these studies have examined only one or two polymorphisms in a defined population, which provides a lack of a general view of the Alzheimer's disease genetic component. OBJECTIVE: To overcome this limitation, nine polymorphisms in seven different candidate genes (A2M, ACT, APOE, APP, BH, HSP70-2, and IL1-A) were genotyped. METHODS: The sample comprised 112 Alzheimer's disease patients and 89 controls from Spain. Since haplotype reconstruction may add power to association studies, we also tested for linkage disequilibrium within the A2M and APOE genes. RESULTS: Except for the APOE gene, allele and genotype frequencies were not different between cases and controls, even when stratifying for the APOE genotype. CONCLUSION: The present results suggest that future association studies should be performed using a battery of polymorphisms in different and new candidate genes, taking into account the linkage disequilibrium in the region.

Alzheimer Disease↗

PubMed2003

HSP70-2 (HSPA1B) is associated with noncognitive symptoms in late-onset Alzheimer's disease.

Neuropsychiatric manifestations are common in Alzheimer's disease (AD) and their phenotypic expression might be related to physiopathological and genetic causes. Multiple studies have implicated oxidative stress to the pathogenesis and possible etiology of AD. One of the mechanisms to protect cells from oxidative stress is the expression of heat-shock proteins (HSP). HSPA1B (alternatively known as HSP70-2) has been related to AD pathophysiology. In the present analysis, 77 AD patients were classified according to their cognitive status with the Neuropsychiatric Inventory and were genotyped for an insertion/deletion (A1/A2) polymorphism. The A2 allele conferred a significant increase of psychiatric morbidity in an allele-dose manner (P < .05). This pattern can be attributed to all AD stages and the severity of the behavioral disturbances was higher for those patients carrying one or two A2 alleles. These results indicate a possible association between the A2 allele and an overexpression of noncognitive symptoms in AD.

Age Factors↗

PubMed2002

A global perspective on genetic variation at the ADH genes reveals unusual patterns of linkage disequilibrium and diversity.

Variants of different Class I alcohol dehydrogenase (ADH) genes have been shown to be associated with an effect that is protective against alcoholism. Previous work from our laboratory has shown that the two sites showing the association are in linkage disequilibrium and has identified the ADH1B Arg47His site as causative, with the ADH1C Ile349Val site showing association only because of the disequilibrium. Here, we describe an initial study of the nature of linkage disequilibrium and genetic variation, in population samples from different regions of the world, in a larger segment of the ADH cluster (including the three Class I ADH genes and ADH7). Linkage disequilibrium across approximately 40 kb of the Class I ADH cluster is moderate to strong in all population samples that we studied. We observed nominally significant pairwise linkage disequilibrium, in some populations, between the ADH7 site and some Class I ADH sites, at moderate values and at a molecular distance as great as 100 kb. Our data indicate (1) that most ADH-alcoholism association studies have failed to consider many sites in the ADH cluster that may harbor etiologically significant alleles and (2) that the relevance of the various ADH sites will be population dependent. Some individual sites in the Class I ADH cluster show Fst values that are among the highest seen among several dozen unlinked sites that were studied in the same subset of populations. The high Fst values can be attributed to the discrepant frequencies of specific alleles in eastern Asia relative to those in other regions of the world. These alleles are part of a single haplotype that exists at high (>65%) frequency only in the eastern-Asian samples. It seems unlikely that this haplotype, which is rare or unobserved in other populations, reached such high frequency because of random genetic drift alone.

Alcohol Dehydrogenase↗

PubMed2002

Determination of haploid DNA sequences in humans: application to the glucocerebrosidase pseudogene.

Variation analyses in the human genome at the sequence level, especially human genetic population analysis and genetic epidemiology, are hampered by the difficulty to ascertain haplotypes on autosomal regions. We have designed a new methodological approach to obtain autosomal haploid sequences from diploid organisms. First, genotypes are unambiguously determined through long-range PCR and diploid DNA sequencing. Second, cloning the whole PCR-amplified segment and sequencing a single clone for those fragments that presented a heterozygous position discern the allelic phase. The second allele is deduced from the genotype, and the phase reconfirmed by sequencing a second clone. A hundred human chromosomes were analysed for a 5.4 kb encompassing the glucocerebrosidase pseudogene on human chromosome 1. Haplotypes were unambiguously ascertained for all samples. The manner to combine the used techniques makes this approach a novelty. Haploid sequences from diploid organisms are obtained in a less time consuming and more accurate manner than in other used procedures.

Glucosylceramidase↗

PubMed2002

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Evolution, Molecular↗