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Biomedical subjects

E Pollak

Publications and source records attributed to E Pollak.

At least 19 recordsLinked to original sources
PubMed2006

The Haemo-QoL Index: developing a short measure for health-related quality of life assessment in children and adolescents with haemophilia.

As quality of life (QoL) research is increasingly focusing on children and adolescents with haemophilia, the need for both age-appropriate and disease-specific assessment tools becomes apparent. Therefore, a set of questionnaires measuring QoL in children and adolescents with haemophilia was simultaneously developed in six languages within the European Haemo-QoL project (Haemophilia, 8, 2002, 47; Haemophilia, 10, 2004, 17). For implementation in larger studies and for use in daily clinical routine, a both short and psychometrically robust version of the questionnaire is needed. Using from the Haemo-QoL field study complete data sets of 306 children and adolescents (4-16 years) and their parents, a multivariate approach of item selection was applied to construct an eight-item instrument, the Haemo-QoL Index. The instrument is applicable to different age groups and represents the core content as well as the multidimensional structure of the original long versions. According to preliminary analyses, the index's psychometric performance concerning reliability and convergent validity is good. Further validation of the instrument's performance on a new and independent sample is needed.

Adolescent↗
PubMed2000

Fixation probabilities when the population size undergoes cyclic fluctuations.

Let us assume that there is a monoecious random mating population that changes cyclically in size. Then, the probability that a nonrecessive favorable mutant is ultimately fixed, if it is originally present in a single heterozygote, is approximately proportional to the harmonic mean of the effective population sizes in the cycle and inversely proportional to the population size when the mutant appears. This approximation works well if the selective advantage s of the mutant is small and the length k of a cycle is small in comparison with the population sizes in a cycle. If k is large the harmonic mean is, in general, replaced by a weighted harmonic mean that puts the largest weights on reciprocals of effective population sizes in the first few generations after the mutant appears.

Alleles↗
PubMed2000

The effective number of a population that varies cyclically in size. I. Discrete generations.

We consider a dioecious population having numbers of males and females that vary over time in cycles of length k. It is shown that if k is small in comparison with the numbers of males and females in any generation of the cycle, the effective population number (or size), N(e), is approximately equal to the harmonic mean of the effective population sizes during any given cycle. This result holds whether the locus under consideration is autosomal or sex-linked and whether inbreeding effective population numbers or variance effective population numbers are involved in the calculation of N(e). If, however, only two successive generations in the cycle are considered and the population changes in size between these generations, the inbreeding effective population number, N(eI), differs from the variance effective population number, N(eV). The mutation effective population number turns out to be the same as the number derived using calculations involving probabilities of identity by descent. It is also shown that, at least in one special case, the eigenvalue effective population number is the same as N(eV).

Alleles↗
PubMed2000

The effective population size of some age-structured populations.

It was shown in a previous paper that if generations are discrete, then the effective population size of a large population can be derived from the theory of multitype branching processes. It turns out to be proportional to the reciprocal of a term that appears in the denominator of expressions for survival probabilities when there is a supercritical positively regular branching process for which the dominant positive eigenvalue of the first moment matrix is slightly larger than 1. If there is an age-structured population with unchanging proportions among sexes and age groups, then the effective population size is shown to be also obtainable from the theory of multitype branching processes. The expression for this parameter has the same form as in the corresponding model for discrete generations, multiplied by an appropriate measure of the average length of a generation. Results are obtained for dioecious random mating populations, populations reproducing partly by selfing, and populations reproducing partly by full-sib mating.

Age Factors↗
PubMed1999

On the theory of partially inbreeding finite populations. VI. The survival probability of a two-locus allele combination when there is partial selfing.

Consider a large population with two loci that may be linked, with one having alleles A and a and the second alleles B and b. Let there be initially one individual with genotype AB/ab in a population otherwise consisting of ab/ab individuals. We assume that AB/ab, Ab/aB, AB/aB, AB/Ab and AB/AB individuals have higher probabilities of survival to adulthood than individuals with genotype ab/ab. The probability that AB ultimately survives, if there is a positive probability of selfing, is calculated. To simplify calculations, it is assumed that the number of offspring produced by any individual follows a Poisson distribution and that genotypes of separate offspring are independent. If recombination is possible, we conclude that a population with a high probability of selfing is more likely to accumulate epistatically favorable genes than one reproducing largely by random mating. This advantage of selfing becomes more pronounced as the strength of selection in favor of AB increases.

Alleles↗
PubMed1998

On the theory of partially inbreeding finite populations. V. The effective size of a partially selfing age-structured population.

Consider a large population, with the same age distribution at times 0, 1, 2, ..., in which there is reproduction by selfing with probability beta and by random mating with probability 1-beta. An individual between i and i + 1 units of age at time t is said to be in age group i at that time. Let L be the mean, among copies of an allele A in genotypes of offspring in age group 0, of ages of parents when the inbreeding coefficient has attained an equilibrium value. Then if there is no selection and allele A is originally present in one heterozygote, the probability that it is ultimately fixed is 1/(2N0L), where N0 is the number of individuals in age group 0 at any time. The effective population size can then be derived. It turns out to be the same as for a population with discrete generations having the same mean and variance of the number of successful gametes produced during a lifetime and the same number of individuals entering the population per generation.

Age Distribution↗
PubMed1997

Calretinin in neurochemically well-defined cell populations of rabbit retina.

In the rabbit retina, parvalbumin has been localized selectively to AII amacrine cells, while 28 kDa calbindin could be detected in horizontal cells, in one type of depolarizing cone bipolar cell and a population of wide-field amacrine cells. The distribution of the third neuronal calcium binding protein, calretinin, however, has not been studied to date in detail in the rabbit retina. Therefore in this study we aimed to describe the overall distribution of calretinin in the different retinal layers and the possible colocalization pattern with other neurochemical marker molecules. A few cone photoreceptor cells were found to be labeled, whereas the outer plexiform layer was free from immunoreactive elements. In the most proximal row of the inner nuclear layer amacrine cells were labeled, while more distally a few cells emitted beaded axon-like processes toward the outer retina. There were large (18-28 microm in diameter) cells labeled in the ganglion cell layer, of which many apparently had their axon stained. Some of the calretinin immunoreactive amacrine cells (the AII neurons) also contained parvalbumin. Colocalization of calretinin and 28 kDa calbindin could not be ascertained in the same amacrine cell populations, nor was tyrosine hydroxylase present in calretinin-containing cells. There was partial colocalization of calretinin in the gamma-aminobutyric acid-positive amacrine cell population. Parvalbumin containing ganglion cells were also positive for calretinin; however, the calretinin-positive ganglion cells were more numerous. gamma-Aminobutyric acid could be colocalized in some calretinin-positive neurons of the ganglion cell layer.

Animals↗
PubMed1996

On the theory of partially inbreeding finite populations. IV. The effective population size for polyploids reproducing by partial selfing.

Consider a population of size N in which there is reproduction by selfing with probability beta and by random mating with probability 1-beta. In each cell of any individual, homologous chromosomes appear 2n times, with n among them having been contributed by each parent. Wright [Proc. Natl. Acad. Sci. 24:372 (1938)] showed that if beta = 0, there is no double reduction in gamete formation, and a Poisson offspring distribution, the probability of nonidentity by descent of two random copies of a gene in an individual of generation t + 1 is approximately 1-1/2nN times as large as it is in generation t if N is large. This result will be generalized to populations with any beta > or = 0 and any offspring distribution. If n = 2 or 3, a result will be obtained that also holds for any probability of double reduction.

Inbreeding↗
PubMed1995

The effect of renal function on serum levels of CA 125.

OBJECTIVE: Serum assays for CA 125 are used to monitor disease status in patients undergoing treatment for epithelial ovarian cancer. While a number of benign gynecologic as well as benign and malignant nongynecologic conditions are associated with CA 125 elevations, the established "normal" range describes a healthy population of women. The metabolism and clearance of CA 125 is not well understood. Because mild degrees of renal impairment frequently occur in ovarian cancer patients, we investigated the effect of impaired renal function on basal CA 125 in a population of female dialysis patients. METHODS: Twenty-five women on hemodialysis were selected at random. Patients ranged in age from 29 to 87 years. Renal disease was secondary in most cases to diabetes mellitus or hypertension. The creatinine clearance was less than 10 cc/min for all patients. The duration of dialysis ranged from 3 months to 14 years. Serum levels of CA 125 were measured using monoclonal antibodies in an immunoradiometric assay. RESULTS: The mean of duplicate determinations for 23 of 25 (92%) patients fell within the normal range for otherwise healthy women (< 35 U/ml). There was no apparent correlation between CA 125 level and age, menopausal status, BUN, serum creatinine, adequacy of dialysis, or primary underlying diagnosis. Of the 2 patients (8%) with CA 125 levels above the normal range, 1 was premenopausal and the other was postmenopausal; their CA 125 elevations were marginal (49.81 and 50.51). CONCLUSIONS: The results of this study demonstrate that even marked renal insufficiency is not itself associated with significant elevations of CA 125 above the normal range selected for otherwise healthy women. The development of renal insufficiency during treatment for ovarian cancer should not alter the interpretation of serum levels of CA 125.

Adult↗
PubMed1995

Some effects of selection when there is partial full-sib mating.

If there is selection only for viability between zygote formation and adulthood, the frequency of a particular allele changes between these two stages of life. With complete mating this is all that happens, but if there is a positive probability that full sibs mate, there is an extra change between adulthood and the appearance of zygotes in the next generation. This occurs because there are then correlated frequencies of the alleles carried by the mates. An expression for the change in the frequency of an allele, which incorporates these two effects, is derived, and the result is found to be consistent with earlier work by the author on the probability of survival of a rare allele in a large population. The result is inconsistent with the usual expression for the change in frequency of an allele when there is partial inbreeding because that expression does not incorporate the second change in frequency within one generation.

Gene Frequency↗