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At least 775 records · Page 43Linked to original sources
PubMed2005

Association between vitamin D receptor FokI. Polymorphism and serum parathyroid hormone level in patients with chronic renal failure.

We investigated the relationship between vitamin D receptor (VDR) start codon polymorphism and serum levels of PTH, calcidiol, and calcium in 64 Spanish patients with chronic renal failure (CRF). An exon 2 fragment of the VDR gene was amplified by PCR, and cleaved with the restriction enzyme FokI. The alleles were identified according to the digestion pattern obtained as F (absence of restriction site) and f (presence of restriction site). Genotype frequencies in the patient population were 54.7% FF, 28.1% Ff and 17.2% ff, vs 46.7% FF, 43.3% Ff and 10% ff in a healthy control population. The difference between the two populations was statistically significant (p<0.01). Within the patient population, mean serum PTH level in the FF group was significantly higher (159.77+/-25.69 pg/ml) than in both the Ff and ff groups (106.67+/-19.07 and 77.55+/-15.85 pg/ml, respectively; p<0.05). However there were no significant differences in serum levels of calcidiol or calcium among genotypes. These results suggest that FokI polymorphisms of the VDR gene may determine parathyroid response in CRF patients.

Calcifediol↗
PubMed2001

Genetic diversity within and among Pinus pinaster populations: comparison between AFLP and microsatellite markers.

Twenty-three populations of Pinus pinaster (13 Aquitaine populations and 10 Corsican populations) were analysed at three microsatellite loci and 122 AFLP loci. The aims of the study were: (i) to compare levels of within-population and among-population diversity assessed with both kinds of markers; (ii) to compare Aquitaine and Corsican provenances of P. pinaster; and (iii) to know if both markers gave the same information for conservation purposes. Classical population genetics statistics were estimated and the ranking of populations obtained using different markers and/or parameters were compared by computing Spearman's rank correlations. Even though microsatellites showed a higher within-population diversity, they showed the same level of differentiation as AFLP markers. Moreover, both markers also showed a higher genetic diversity in the Aquitaine provenance and a higher differentiation among Corsican populations. AFLPs and microsatellites gave different population diversity rankings. Consequently, the results do not support the potential population identification within each provenance for conservation purposes.

Alleles↗
PubMed2000

An audit of current clinical practice in the management of osteoporosis in Nottingham.

BACKGROUND: Osteoporosis is now recognized by the World Health Organization and the Department of Health as a major public health problem. In 1994, the Advisory Group on Osteoporosis (AGO), set up by the Department of Health, recommended that Health Authorities and general practitioner fundholders should purchase bone densitometry services for the management of osteoporosis. The aims of this study were to assess the criteria for requests for bone densitometry from primary care in comparison with the AGO recommendations and to compare the numbers of patients referred with a low-trauma osteoporotic fracture with the expected number of fractures in the Nottingham area. METHODS: Patient referral data and requests for bone densitometry were collected by case note review of all new patients referred to the Nottingham Osteoporosis Clinic over a 12 month period and then compared with the AGO recommendations. The patients referred with a history of a low-trauma fracture were then compared with the expected incidence of fractures, calculated using age-sex-specific fracture incidence data applied to the Nottingham population Census statistics. RESULTS: A total of 413 patients were referred to the Osteoporosis Clinic for bone densitometry. Almost two-thirds of the patients had no clinical indicators for requests for scanning, in comparison with the AGO recommendations. Seventy-seven patients were referred with vertebral fracture, 12 hip, 20 colles and 26 other fractures. Using age-sex-specific fracture incidence data applied to the Nottingham population Census statistics, it was estimated that the expected incidence of hip fractures would be 812, distal forearm fractures 514 and vertebral fractures presenting to clinical attention 625. This represents 1.5 per cent of the total hip fractures, 3.9 per cent distal forearm and 12.3 per cent vertebral actually presenting to the Osteoporosis Clinic. CONCLUSION: Bone densitometry was requested in up to 60 per cent of the patients with no clinical risk factors to warrant bone densitometry. Osteoporosis-related fractures remain unrecognized in clinical practice. The majority of patients do not receive specialist assessment despite being at high risk of future fracture. Further steps are necessary to educate health care professionals in primary and secondary care, but more importantly, to direct services more proactively in those at high risk of future fracture.

Absorptiometry, Photon↗
PubMedDate not supplied

Frequency of CYP21 gene mutations in Czech patients with steroid 21-hydroxylase deficiency and statistical comparison with other populations.

OBJECTIVE: To undertake mutational analysis in patients with different forms of steroid 21-hydroxylase deficiency. SUBJECTS AND METHODS: CYP21 gene molecular analysis was performed in 76 Czech patients diagnosed with steroid 21-hydroxylase deficiency. Eight of the most common point mutations (intron 2 splice, P30L, 8bp deletion in exon 3, I172N, V281L, Q318X, R356W, and P453S) were analyzed using an amplification-created restriction site method, and 5 additional mutations (intron 7 splice, F307insT, cluster in exon 6, R484P, and R484X) were analyzed using dot-blot hybridization with 5'-biotin-labeled oligonucleotides. Deletions and conversions were screened using a sequence-specific oligonucleotide hybridization method. Comparison of common mutation frequencies in CYP21 reported for different regions, both within Europe and worldwide (North and South America, Asia, and North Africa), was undertaken and the significance of the differences was determined by statistical analysis (Fisher's F test, Student's t test, paired t test, and confidence intervals) using a value of p < 0.05. RESULTS: The most frequent genetic defect found in this group of Czech patients was intron 2 splice mutation (46.7%). Comparison of mutation frequencies between Czech and other European populations showed that the Czech patients had a lower frequency of deletions/large gene conversions, R356W, and cluster mutations in exon 6, together with a higher frequency of intron 2 splice mutation, 8-bp deletion and F307insT compared with other populations. CONCLUSION: A high prevalence of P30L mutations, mostly associated with nonclassical forms of congenital adrenal hyperplasia, was found in Czech patients with classic simple virilizing forms of steroid 21-hydroxylase deficiency.

Czech Republic↗
PubMed1999

Some statistical improvements for estimating population size and mutation rate from segregating sites in DNA sequences.

In population genetics, under a neutral Wright-Fisher model, the scaling parameter straight theta=4Nmu represents twice the average number of new mutants per generation. The effective population size is N and mu is the mutation rate per sequence per generation. Watterson proposed a consistent estimator of this parameter based on the number of segregating sites in a sample of nucleotide sequences. We study the distribution of the Watterson estimator. Enlarging the size of the sample, we asymptotically set a Central Limit Theorem for the Watterson estimator. This exhibits asymptotic normality with a slow rate of convergence. We then prove the asymptotic efficiency of this estimator. In the second part, we illustrate the slow rate of convergence found in the Central Limit Theorem. To this end, by studying the confidence intervals, we show that the asymptotic Gaussian distribution is not a good approximation for the Watterson estimator.

Base Sequence↗
PubMed1994

Collective adaptation in a statistical model of an evolving population.

We simulate asexually and sexually reproducing model populations evolving in a rugged fitness landscape where fit and unfit genotypes are distributed at random, and where all fit genotypes have the same a priori probability of reproduction. Varying the fraction chi of unfit genotypes at a fixed mutation rate we observe a strikingly different behavior for the two reproduction mechanisms. For the asexually reproducing population, the effective mutation rate lambda decreases roughly proportionally to (1-chi), and the fraction delta of sterile individuals--processing an unfit genotype--accordingly increases roughly proportionally to chi. On the other hand, lambda remains approximately constant (and delta increases proportionally to chi) for small values of chi:but, at a critical value chi*, both lambda and delta suddenly drop. This corresponds to the transition to an adaptive regime where the average fitness of the population is enhanced. We show how this transition can be interpreted in terms of an improvement of the collective fitness of the population.

Biological Evolution↗
PubMed2006

Benchmarking performance in organ donation programs: dependence on demographics and mortality rates.

PURPOSE: Donors whose diagnosis of death is based upon neurologic criteria are the primary source of organs for human transplantation. The current measure of effectiveness of organ donation programs is the crude statistic, donors per million population (DPMP). This statistic represents the number of available donors, divided by the potential donor population. Comparisons between transplantation programs are done using the DPMP statistic. We sought to determine if variance in organ donation rates, reported as DPMP could be accounted for by differences in population demographics, specifically age and gender-specific mortality rates. METHODS: We obtained the population distribution and deaths for the year 2000 for the Calgary Health Region (CHR) and the country of Spain. Expected deaths were then calculated by standardizing the sample, based upon weighted averages of age, gender and cause-specific mortality rates. RESULTS: In 2000, Spain reported a crude organ donation rate of 33.9 DPMP. Standardizing the observed deaths in Spain using the CHR population distribution and calculating expected deaths based on the CHR rates, resulted in an adjusted rate of 19.2 DPMP (P < 0.05). CONCLUSIONS: These results bring into question the reliability of using crude DPMP as a measure of organ and tissue donation program performance. Alternative measures of benchmarking performance in organ donation programs should be considered.

Adolescent↗
PubMed1998

Statistically efficient estimation using population coding.

Coarse codes are widely used throughout the brain to encode sensory and motor variables. Methods designed to interpret these codes, such as population vector analysis, are either inefficient (the variance of the estimate is much larger than the smallest possible variance) or biologically implausible, like maximum likelihood. Moreover, these methods attempt to compute a scalar or vector estimate of the encoded variable. Neurons are faced with a similar estimation problem. They must read out the responses of the presynaptic neurons, but, by contrast, they typically encode the variable with a further population code rather than as a scalar. We show how a nonlinear recurrent network can be used to perform estimation in a near-optimal way while keeping the estimate in a coarse code format. This work suggests that lateral connections in the cortex may be involved in cleaning up uncorrelated noise among neurons representing similar variables.

Computer Simulation↗
PubMed1993

[Demographic review of the Netherlands, 1992].

Demographic trends in the Netherlands during 1992 are reviewed. Among the findings, the author notes that "in 1992 the Dutch population grew by 110 thousand.... The number of births fell by some 2 thousand, immigration by 3.5 thousand. The number of deaths remained unchanged. Emigration increased by 1.5 thousand.... Twelve per cent of the population live in a one person household. Thirty years ago this was only 3%. Due to the decreased average number of children per family the proportion of children fell from 44% in 1960 to 30% in 1992. The number of people who were born abroad shows an annual growth of 4.4%. The growth of the native population is 0.44% per year.... Fertility is highest for 30 year old women. In 1970 this was the case for those who were 26 years of age." (SUMMARY IN ENG)

Age Factors↗
PubMed1996

Measurement of genetic structure within populations using Moran's spatial autocorrelation statistics.

Spatial structure of genetic variation within populations, an important interacting influence on evolutionary and ecological processes, can be analyzed in detail by using spatial autocorrelation statistics. This paper characterizes the statistical properties of spatial autocorrelation statistics in this context and develops estimators of gene dispersal based on data on standing patterns of genetic variation. Large numbers of Monte Carlo simulations and a wide variety of sampling strategies are utilized. The results show that spatial autocorrelation statistics are highly predictable and informative. Thus, strong hypothesis tests for neutral theory can be formulated. Most strikingly, robust estimators of gene dispersal can be obtained with practical sample sizes. Details about optimal sampling strategies are also described.

Biological Evolution↗
PubMedDate not supplied

From a theoretical framework of human exposure and dose assessment to computational system implementation: the Modeling ENvironment for TOtal Risk Studies (MENTOR).

Georgopoulos and Lioy (1994) presented a theoretical framework for exposure analysis, incorporating multiple levels of empirical and mechanistic information while characterizing/reducing uncertainties. The present review summarizes efforts towards implementing that framework, through the development of a mechanistic source-to-dose Modeling ENvironment for TOtal Risks studies (MENTOR), a computational toolbox that provides various modeling and data analysis tools to facilitate assessment of cumulative and aggregate (multipathway) exposures to contaminant mixtures. MENTOR adopts a "Person Oriented Modeling" (POM) approach that can be applied to either specific individuals or to populations/subpopulations of interest; the latter is accomplished by defining samples of "virtual" individuals that statistically reproduce the physiological, demographic, etc., attributes of the populations studied. MENTOR implementations currently incorporate and expand USEPA's SHEDS (Stochastic Human Exposure and Dose Simulation) approach and consider multiple exposure routes (inhalation, food, drinking water intake; non-dietary ingestion; dermal absorption). Typically, simulations involve: (1) characterizing background levels of contaminants by combining model predictions and measurement studies; (2) characterizing multimedia levels and temporal profiles of contaminants in various residential and occupational microenvironments; (3) selecting sample populations that statistically reproduce essential demographics (age, gender, race, occupation, education) of relevant population units (e.g., census tracts); (4) developing activity event sequences for each member of the sample by matching attributes to entries of USEPA's Consolidated Human Activity Database (CHAD); (5) calculating intake rates for the sample population members, reflecting physiological attributes and activities pursued; (6) combining intake rates from multiple routes to assess exposures; (7) estimating target tissue doses with physiologically based dosimetry/toxicokinetic modeling.

Complex Mixtures↗
PubMed1977

Influence of population on the classification of ECG-VCG's using linear regression techniques.

This paper describes the influence of different populations on statistical multivariate classification rules and classification results where the word "population" refers only to the frequency of diagnoses to be expected, the so-called prior probabilities. Using linear regression as a multivariate classification technique and six groups consisting of five pathological conditions and normals as test data, it has been shown: (a) That the population influences to a great extent the selection of the best ECG-VCG measurements for the classification rule. (b) That a mismatch of the populations in the learning and test sets can considerably decrease the number of correct classifications. (c) That a certain correction of the mismatch can be achieved when the prior probabilities in the learning and test sets are known, Further, the paper discusses the change of prior probabilities over the years at the Variety Club Heart Hospital in the University of Minnesota and its effect on the performance of the classification algorithm which has been used.

Electrocardiography↗
PubMed1991

HIV-1 seropositivity and mortality at University Hospital, Kinshasa, Zaire, 1987.

This study examines the impact of HIV-1 infection and AIDS on 500 of 563 consecutive deaths at University Hospital, Kinshasa, Zaire, in late 1987. HIV-1 seroprevalence was 31% for the entire population and 43% for the 247 adults. Forty-two (38%) of the 110 HIV-1-seropositive adult deaths occurred in those between the ages of 25 and 34 years. The mean age of death for seropositives was 36 years, 7.5 years less than seronegative deaths. AIDS and AIDS-associated diagnoses such as cryptococcal meningitis, chronic diarrhea and pneumonia accounted for 42% of all adult deaths and 74% of all HIV-1-seropositive adult deaths. Seventeen per cent of 50 sera initially negative by enzyme-linked immunosorbent assay (ELISA) were ultimately found to be HIV-1-seropositive by Western blot or p24 antigen testing. The data indicate that HIV-1 infection and AIDS contribute significantly to adult mortality in Kinshasa population and that sensitivity of ELISA tests decreases in terminal HIV-1 infection.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Prediction of anticoagulation during hemodialysis by population kinetics and an artificial neural network.

All systems currently used for routine hemodialysis require heparin administration to prevent blood clotting in the extracorporeal circuit. We tested the hypothesis that population-based statistical techniques can be used to predict heparin concentrations during routine hemodialysis. Two predictive models were developed, one based on nonlinear mixed effects modeling (NONMEM) and the other on a multilayer perceptron neural network. Serial clotting time data were obtained from forty-nine patients and used to develop the models. The models were used to predict the clotting times of 70 patients in a prospective test. We determined that the neural network provided greater precision, had fewer outliers in its predictions, and did not have the model misspecification in bolus administration that the NONMEM predictions demonstrated. A final NONMEM model was developed using all data from 119 patients to identify important covariates for predicting the heparin pharmacodynamic parameters, volume of distribution, and clearance. Both the volume of distribution and clearance increased following the initiation of dialysis and as the patient's baseline clotting time increased. The volume of distribution also increased as the patient's weight increased but was decreased by smoking and diabetes. Population-based statistical techniques may provide a useful alternative to existing methods for prescribing heparin.

Adult↗
PubMed2003

Human genetic diversity and the nonexistence of biological races.

Sewall Wright's population structure statistic, F(ST), measured among samples of world populations is often 15% or less. This would indicate that 85% of genetic variation occurs within groups while only 15% can be attributed to allele frequency differences among groups. In this paper, we show that this low value reflects strong biases that result from violating hidden assumptions that define F(ST). These limitations on F(ST) are demonstrated algebraically and in the context of analyzing dinucleotide repeat allele frequencies for a set of eight loci genotyped in eight human groups and in chimpanzees. In our analyses, estimates of F(ST) fail to identify important variation. For example, when the analysis includes only humans, F(ST) = 0.119, but adding the chimpanzees increases it only a little, F(ST) = 0.183. By relaxing the underlying statistical assumptions, the results for chimpanzees become consistent with common knowledge, and we see a richer pattern of human genetic diversity. Some human groups are far more diverged than would be implied by standard computations of F(ST), while other groups are much less diverged. We discuss the relevance of these findings to the application of biological race concepts to humans. Four different race concepts are considered: typological, population, taxonomic, and lineage. Surprisingly, a great deal of genetic variation within groups is consistent with each of these concepts. However, none of the race concepts is compatible with the patterns of variation revealed by our analyses.

Chi-Square Distribution↗