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Biomedical subjects

M W Smith

Publications and source records attributed to M W Smith.

At least 37 records · Page 2Linked to original sources
PubMed2000

Genetic restriction of HIV-1 pathogenesis to AIDS by promoter alleles of IL10.

IL10 is a powerful TH-2 cell cytokine produced by lymphoid cells that limits HIV-1 replication in vivo, ostensibly by inhibiting macrophage/monocyte and T-cell lymphocyte replication and secretion of inflammatory cytokines (IL1, TNFalpha, IL6, IL8, and IL12). A genetic epidemiological scan of patients enrolled in AIDS cohorts for candidate gene-linked short tandem repeat polymorphisms revealed significant genotype associations for HIV-1 infection and progression to AIDS with markers adjacent to and tracking (by linkage disequilibrium) common single nucleotide polymorphic variants in the IL10 promoter region. Individuals carrying the IL10-5'-592A (IL10-5'A) promoter allele possibly were at increased risk for HIV-1 infection, and once infected they progressed to AIDS more rapidly than homozygotes for the alternative IL10-5'-592 C/C (IL10-+/+) genotype, particularly in the later stages of HIV-1 infection. An estimated 25-30% of long-term nonprogressors (who avoid clinical AIDS for 10 or more years after HIV-1 infection) can be attributed to their IL10-+/+ promoter genotype. Alternative IL10 promoter alleles are functionally distinct in relative IL10 production, in retention of an avian erythroblastosis virus transcription factor recognition sequence and in binding to specific putative nuclear transcription factors, suggesting a potential mechanism whereby IL10-5'A down-regulation of inhibitory IL10 facilitates HIV-1 replication in vivo, accelerating the onset of AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Influence of CCR5 promoter haplotypes on AIDS progression in African-Americans.

OBJECTIVES: To test the hypothesis that the CCR5 promoter variants in HIV-1-infected African-Americans affect the rate of progression to AIDS and to determine the extent of linkage disequilibrium between the CCR5P1 allele and the CCR5 59029A variant (referred to here as CCR5-2459A), both of which have been shown independently to accelerate AIDS progression in Caucasians. DESIGN: We used survival analysis to assess the effects of CCR5 promoter variants in HIV-1 seroincident Caucasians and African-Americans. SUBJECTS AND METHODS: Genotypes were determined for 806 Caucasians and 1067 African-Americans, which included 700 seroconverters, enrolled in four HIV/AIDS natural history cohort studies. These genotypes were used to determine linkage and haplotypes for CCR2 and CCR5 alleles. Survival analysis was used to assess the effect of CCR2, CCR5, and CCR5 promoter haplotypes on progression to AIDS in seroincident African-Americans. RESULTS: A survey of Caucasians and African-Americans demonstrated complete linkage disequilibrium between CCR5P1 and CCR5-2459A sites. The composite CCR5P1 haplotype (including the CCR5-2459A allele) is shown to be associated with rapid progression to AIDS endpoints in both African-American and Caucasian cohorts, but the effect is recessive in Caucasians and dominant in African-Americans. This is probably due to the presence of modulating genes or as yet unidentified polymorphisms that may differ between racial groups.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Short tandem repeat methodology for genotypic identification of single-person versus multi-person use of syringes.

OBJECTIVE: To develop laboratory methods to differentiate between single- versus multi-person use of syringes by injection drug users. METHODS: Forensic short tandem repeat (STR) genetic analysis was undertaken to cross-validate a test panel of trace blood contents from syringes representing single- versus multi-person syringe use. Laboratory-simulated scenarios of needle sharing generated 34 syringe washes that were blinded for evaluation. Polymerase chain reaction was used to amplify the polymorphic STR locus D6S502 from blood trace contents in used syringes. Alleles were sized and quantified using a commercial gene sequencer. A statistical algorithm was developed to determine the number of alleles present in the amplified DNA fragments. Syringes with more than two expected alleles were considered to represent multi-person syringe use. Sensitivity, specificity and the kappa coefficient were calculated. RESULTS: Allelic matrix-based analysis of alleles from the single STR successfully characterized single-use (n = 12) and multiple-use (n = 22) syringes with 68% sensitivity and 100% specificity upon re-analysis. The extent of agreement over and above chance (kappa = 0.6; P < 0.0001) indicated good agreement for differentiating single- versus multi-person syringe use. CONCLUSIONS: These findings suggest that improved genotypic STR analysis of syringe material could be an adjunct to methods for validating self-reported needle sharing, conducting behavioral surveillance of needle-sharing behaviors, and evaluating interventions such as needle-exchange programs. Assays based on multiple STR loci will undoubtedly improve upon the promising results obtained from laboratory simulations of needle sharing.

Alleles↗
PubMed2000

Polymorphisms of the human IFNG gene noncoding regions.

Interferon gamma (IFN-gamma) is a multifunctional cytokine that is essential in the development of Th1 cells and in cellular responses to a variety of intracellular pathogens including human immunodeficiency virus (HIV-1). We screened genomic DNA samples from a predominately Caucasian male population of HIV-infected and healthy donors for polymorphisms in the human IFNG gene from -777 to +5608 by single-stranded conformational polymorphism. Surprisingly, the proximal promoter (-777 to transcription start) is invariant as no polymorphisms were found in over 100 samples tested. However, further screening revealed polymorphisms in other regions of the gene including a single base insertion in a poly-T tract in the first intron, three single base pair substitutions in the third intron, and another single base pair substitution in the 3' untranslated region (UTR). Electrophoretic mobility shift assay was used to investigate whether these variants have altered DNA-binding abilities, since intronic enhancer elements have been reported for the IFNG gene. Oligonucleotides constructed for two third intron variants showed no difference in DNA-binding abilities as compared with wild-type sequences. However, the 3'UTR variant showed the formation of unique DNA-binding complexes to radiolabeled oligonucleotide probes as compared with the wild-type sequence. The influence of a CA-repeat microsatellite on AIDS disease progression in HIV-1 seroconverters was tested by a Cox proportional hazards model. There is no evidence of an association between alleles and infection with HIV-1 or progression to AIDS. We report an invariant proximal human IFNG promoter and the existence of multiple intronic variants and a potentially functional 3'UTR polymorphism.

3' Untranslated Regions↗
PubMed2000

Proximally porous coated femoral stem in total hip replacement--5- to 13-year follow-up report.

A series of total hip replacements was performed using a proximally porous coated, tapered femoral stem system. At a mean follow-up of 8.1 (5-13) years, 80 out of 107 hips were available for clinical and radiological examination. The mean age at the index procedure was 58.6 years. The mean Harris Hip Score at final follow-up was 91.7. Radiological ingrowth was observed in 77 femoral stems, 2 stems were fibrous stable and 1 stem was loose.

Female↗
PubMed2000

Cementless hemispheric acetabular component in total hip replacement.

A series of 198 total hip arthroplasties was performed using a porous-coated, hemispheric press-fit cup. One hundred and twenty-seven cups were available for clinical and radiological examination at mean follow-up of 10.6 years. The mean age at the index procedure was 61.2 years. The mean Harris hip score at final follow-up was 89.8. Three cups were revised for aseptic loosening and two liners were changed for eccentric wear and pelvic osteolysis. Nine additional patients showed mild or suspected osteolysis. Two cups were rated "fibrous" stable. There was no correlation between additional screw fixation of the press-fit cup and osteolysis or revision.

Adult↗
PubMed2000

Supracondylar nailing of distal periprosthetic femoral fractures.

Seven patients who sustained complex distal femoral fractures above total knee arthroplasties all treated by supracondylar (retrograde) femoral nailing were retrospectively evaluated. All the patients demonstrated uncomplicated postoperative follow-ups and returned to weight bearing between 2 and 3 months after surgery. No delayed healing occurred and alignment of the femur was satisfactory.

Aged↗
PubMed2000

Structural and cellular adaptation of duodenal iron uptake in rats maintained on an iron-deficient diet.

Iron deficiency induced in rats maintained on a commercial diet with a low iron content has been used to investigate adaptive mechanisms that enhance duodenal iron uptake. These adaptive changes have been divided into those that result from changes in villus surface area (structural adaptation) and those that reflect changes in the way individual enterocytes express iron transport function (cellular adaptation). Cellular adaptation was assessed by carrying out microdensitometry of autoradiographs prepared from duodenal tissue previously incubated for 5 min in 200 micromol/l 59Fe2+-ascorbate. Structural adaptation was studied by performing image analysis of microdissected and sectioned villi. Cellular adaptation involved increased iron uptake by enterocytes present in the lower villus. Thus iron deficiency resulted in a threefold enhanced expression of uptake in the lower 100 microm villus (3.9+/-2.4 versus 12.6+/-1.5 arbitrary units, P<0.001). Maximal uptake was reached in the upper region of both control and iron-deficient villi, but iron deficiency had no effect on cellular uptake at this part of the villus. Structural adaptation involved the lengthening (+16%, P<0.05) and broadening (+14%) of villi in the duodenum of iron-deficient rats. The resultant expansion in villus area caused a further increase in uptake that was mostly expressed in the upper villus. Maximal uptake corrected for structure occurred in the middle third of villi from control and iron-deficient rats. Cellular plus structural adaptation produced a twofold increase in iron uptake. More than half of this effect was caused by changes in villus structure. [3H]Thymidine labelling experiments revealed a slightly earlier expression of enterocyte iron uptake in iron deficiency.

Adaptation, Physiological↗
PubMed2000

Risk adjustment of capitation payments to behavioral health care carve-outs: how well do existing methodologies account for psychiatric disability?

This study used 1994-1995 administrative data from a large public employer to examine the viability of commercial risk adjustment systems for setting capitation payments to competing behavioral health care "carve-outs". The ability of Hierarchical Condition Categories and Adjusted Diagnostic Groups to predict psychiatric expenditures was improved by controlling separately for psychiatric disability. However, even the best models underpredicted expenditures of patients with psychiatric disability by 15%. Relative to full capitation, "mixed" payment systems and soft capitation reduce the ability of carve-outs to earn disproportionate profits by enrolling healthy patients and avoiding sick ones, yet also diminish incentives for cost containment.

Adult↗
PubMed2000

Significant admixture linkage disequilibrium across 30 cM around the FY locus in African Americans.

Scientists, to understand the importance of allelic polymorphisms on phenotypes that are quantitative and environmentally interacting, are now turning to population-association screens, especially in instances in which pedigree analysis is difficult. Because association screens require linkage disequilibrium between markers and disease loci, maximizing the degree of linkage disequilibrium increases the chances of discovering functional gene-marker associations. One theoretically valid approach-mapping by admixture linkage disequilibrium (MALD), using recently admixed African Americans-is empirically evaluated here by measurement of marker associations with 15 short tandem repeats (STRs) and an insertion/deletion polymorphism of the AT3 locus in a 70-cM segment at 1q22-23, around the FY (Duffy) locus. The FY polymorphism (-46T-->C) disrupts the GATA promoter motif, specifically blocking FY erythroid expression and has a nearly fixed allele-frequency difference between European Americans and native Africans that is likely a consequence of a selective advantage of FY-/- in malaria infections. Analysis of linkage disequilibrium around the FY gene has indicated that there is strong and consistent linkage disequilibrium between FY and three flanking loci (D1S303, SPTA1, and D1S484) spanning 8 cM. We observed significant linkage-disequilibrium signals over a 30-cM region from -4.4 to 16.3 cM (from D1S2777 to D1S196) for STRs and at 26.4 cM (AT3), which provided quantitative estimates of centimorgan limits, by MALD assessment in African American population-association analyses, of 5-10 cM.

Africa↗
PubMed2000

Results of all-polyethylene tibial components as a cost-saving technique.

Since 1992, the authors have used an all polyethylene tibial component in relatively less active patients older than 70 years of age who present for primary total knee replacement. Results of 312 knee replacements performed between March 1992 and March 1998 are presented in the hopes of showing this technique as a viable cost saving measure. Three hundred twelve primary total knee replacements were performed by the same group of surgeons. Fourteen patients died before the first year postoperative evaluation, leaving an index group of 298 knees in 231 patients. All components were evaluated using the radiographic and clinical parameters of the Knee Society. Hospital for Special Surgery scores also were calculated. All patients were given the Short Form-36 Quality of Life Assessment preoperatively and annually postoperatively. Clinical scores showed dramatic improvement. There have been three revisions (0.7%) but none were for aseptic loosening. Radiographic review revealed 295 replacements with optimum fixation. To date, no patient has osteolysis. The cost differential was significant. The use of this type of tibial component has, to date, afforded excellent clinical and radiographic results. Additional followup is needed to show the longevity of these results and to monitor wear or subsidence of these prostheses. Should these results continue to prove satisfactory in this particular group of patients with relatively low physical demands, significant cost savings may be realized.

Aged↗
PubMed2000

The impact of the Citibank, NA, health management program on changes in employee health risks over time.

This study estimated the impact of the Citibank Health Management Program on changes in health risks among Citibank employees. McNemar chi-squared tests compared the probability of being at high risk for poor health when the first and last health-risk appraisal surveys were taken. Logistic regression controlled for baseline differences in subsequent analyses when those who participated in more intensive program features were compared with those who participated in less intensive features. Declines in risk were noted for 8 of 10 risk categories. Most changes were small, except those related to exercise habits, seatbelt use, and stress levels. For nine health risk categories, those who participated in more intensive program services were significantly more likely than others to reduce their health risks. Thus, the Citibank Health Management Program was associated with significant reductions in health risk.

Adolescent↗
PubMed2000

Polygenic and multifactorial disease gene association in man: Lessons from AIDS.

In an age when the majority of monogenic human disease genes have been identified, a particular challenge for the coming generation of human geneticists will be resolving complex polygenic and multifactorial diseases. The tools of molecular and population genetic association have much potential as well as peril in uncovering small cryptic genetic effects in disease. We have used a candidate gene approach to identify eight distinct human loci with alleles that in different ways influence the outcome of exposure to HIV-1, the AIDS virus. The successes in these gene hunts have validated the approach and illustrate the strengths and limitations of association analysis in an actual case history. The integration of genetic associations, well-described clinical cohorts, extensive basic research on AIDS pathogenesis, and functional interpretation of gene connections to disease offers a formula for detecting such genes in complex human genetic phenotypes.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Delayed metabolism of human brain natriuretic peptide reflects resistance to neutral endopeptidase.

Metabolism of natriuretic peptides is regulated by two degradative pathways: uptake by the clearance receptor (natriuretic peptide receptor C--NPR-C) and hydrolysis by neutral endopeptidase (NEP). Affinity studies favour a dominant role of NPR-C in hormone degradation in several species but do not account for the efficacy of NEP inhibitors in vivo, nor the uniquely prolonged half life (t((1/2))) of human brain natriuretic peptide (hBNP). Postulating that (1) delayed metabolism of hBNP reflects resistance to NEP and (2) interactions between NPR-C and NEP increase enzyme activity, we have used purified ovine and human NEP, plus ovine lung plasma membranes to study the relative importance of receptor and enzyme pathways. We have also related the findings to hormone metabolism in vivo. Binding affinities of atrial natriuretic peptide (ANP), hBNP and ovine BNP (oBNP) to oNPR-C were similar (K(d)=8-16 pM). In contrast, unlike ANP and oBNP, hBNP was not significantly degraded by purified oNEP or plasma membranes. Despite similar (and high) affinity of oNPR-C for oBNP and hBNP, the t((1/2)) of hBNP (12.7 min) was more than fourfold that of oBNP (2.6 min). Although we found no evidence for receptor-enzyme interaction, our results show that the delayed metabolism of hBNP reflects resistance to NEP. These findings have important implications for future treatment strategies in human disease.

Animals↗
PubMed1999

A signal recognition particle receptor gene from the early-diverging eukaryote, Giardia lamblia.

The molecular mechanisms for targeting and translocation of secreted proteins are highly conserved from bacteria to mammalian cells, although the machinery is more complex in higher eukaryotes. To investigate protein transport in the early-diverging eukaryote, Giardia lamblia, we cloned the gene encoding the alpha subunit (SRalpha) of the signal recognition particle (SRP) receptor. SRalpha is a small GTPase that functions in SRP-ribosome targeting to the ER. Sequence and phylogenetic analyses showed that SRalpha from G. lamblia is most homologous to SRalpha proteins from higher eukaryotes, although it lacks some conserved motifs. Specifically, giardial SRalpha has an N-terminal extension that enables SRalpha of higher eukaryotes to interact with a beta subunit that anchors it in the ER membrane. While the C-terminal regions are similar, giardial SRalpha lacks a prominent 13 amino acid regulatory loop that is characteristic of higher eukaryotic versions. Thus, giardial SRalpha resembles that of higher eukaryotes, but likely diverged before the advent of the regulatory loop. The 1.8 kb SRalpha transcript has extremely short untranslated regions (UTRs): a 1-2 nt 5'- and a 9 nt 3' UTR with the polyadenylation signal overlapping with the stop codon. RT-PCR, Northern and Western analyses showed that SRalpha is present at relatively constant levels during vegetative growth and encystation, even though there are extensive changes in endomembrane structures and secretory activity during encystation. Imnuno-EM showed that SRalpha localizes to ER-like structures, strengthening the observation of a typical ER in G. lamlia. Unexpectedly, SRalpha was also found in the lysosome-like peripheral vacuoles, suggesting unusual protein traffic in this early eukaryote. Our results indicate that the eukaryotic type of cotranslational transport appeared early in the evolution of the eukaryotic cell.

Amino Acid Sequence↗
PubMed1999

Modelling molecular mechanisms controlling sequential gene expression in differentiating mammalian enterocytes.

The gut epithelium represents a continuous developmental system in which cell proliferation in intestinal crypts is followed by the sequential expression of digestive and absorptive functions as enterocytes migrate out of crypts to the tips of intestinal villi. We have developed a mathematical model in the present work to mimic these sequential aspects of enterocyte differentiation. Using this model allows the characteristics of lactase expression to be ascribed to transcriptional control. In the case of a glucose transporter, however, it became necessary to assume an additional translational control that decreased exponentially as enterocytes migrated along villi. The suggestion that this type of modelling is useful in predicting which set of enterocytes is likely to use translation or transcription to control gene expression is also discussed.

Animals↗
PubMed1999

A scan for linkage disequilibrium across the human genome.

Linkage disequilibrium (LD), the tendency for alleles of linked loci to co-occur nonrandomly on chromosomal haplotypes, is an increasingly useful phenomenon for (1) revealing historic perturbation of populations including founder effects, admixture, or incomplete selective sweeps; (2) estimating elapsed time since such events based on time-dependent decay of LD; and (3) disease and phenotype mapping, particularly for traits not amenable to traditional pedigree analysis. Because few descriptions of LD for most regions of the human genome exist, we searched the human genome for the amount and extent of LD among 5048 autosomal short tandem repeat polymorphism (STRP) loci ascertained as specific haplotypes in the European CEPH mapping families. Evidence is presented indicating that approximately 4% of STRP loci separated by <4.0 cM are in LD. The fraction of locus pairs within these intervals that display small Fisher's exact test (FET) probabilities is directly proportional to the inverse of recombination distance between them (1/cM). The distribution of LD is nonuniform on a chromosomal scale and in a marker density-independent fashion, with chromosomes 2, 15, and 18 being significantly different from the genome average. Furthermore, a stepwise (locus-by-locus) 5-cM sliding-window analysis across 22 autosomes revealed nine genomic regions (2.2-6.4 cM), where the frequency of small FET probabilities among loci was greater than or equal to that presented by the HLA on chromosome 6, a region known to have extensive LD. Although the spatial heterogeneity of LD we detect in Europeans is consistent with the operation of natural selection, absence of a formal test for such genomic scale data prevents eliminating neutral processes as the evolutionary origin of the LD.

Alleles↗