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Biomedical subjects

R Chakraborty

Publications and source records attributed to R Chakraborty.

At least 217 records · Page 12Linked to original sources
PubMed1984

Increase of the peroxidase activity of mouse submaxillary gland by reserpine.

The peroxidase activity of mouse submaxillary gland was found to be elevated by about 128% at 22 hr. after the administration of reserpine (0.5 mg/kg). This effect of reserpine was observed in rat also. Neither pretreatment with 6-hydroxy dopamine (6-OH dopamine) nor surgical sympathetic denervation could abolish the increase of the peroxidase activity elicited by reserpine. Also, treatment with propranolol, dibenamine or atropine sulfate failed to reverse the effect of reserpine. These results suggest that neither catecholamine nor acetyl choline is involved in this reserpine action.

Animals↗
PubMed1984

The pathophysiology of neurofibromatosis: IX. Paternal age as a factor in the origin of new mutations.

Von Recklinghausen neurofibromatosis is characterized by a relatively large proportion of apparently nonfamilial cases, presumed spontaneous mutations. This paper analyzes the distribution of paternal and maternal ages for 187 patients with von Recklinghausen disease representing the first definite case in their respective families. Mean paternal age was 32.8 years and mean maternal age was 27.4 years, both being significantly greater than for control populations (P equal to or less than .001). The advanced paternal age was not accounted for by the increase in maternal age. The methodology of controlling the general population paternal ages for each patient's birth year is described.

Adult↗
PubMed1984

Relationship between heterozygosity and genetic distance in the three major races of man.

In pairwise comparisons of gene frequency data from the three major races of man, the single locus measures of the heterozygosity within and the genetic distance between races are shown to be strongly correlated across the loci coding for red cell proteins and enzymes. The intercept of the regression line of genetic distance on heterozygosity in protein enzyme loci is statistically insignificant. These findings suggest that the genetic variability at the enzyme and protein loci in man is probably maintained by a balance of mutation and random genetic drift. At the blood group loci, however, the observed relationship between genetic distance and heterozygosity does not follow the expectation of the neutral mutation hypothesis. These observations are discussed in terms of the changes in probability of identical monomorphism in two populations during the process of gene differentiation.

Blood Group Antigens↗
PubMed1984

A method to detect excess risk of disease in structured data: cancer in relatives of retinoblastoma patients.

It is often of interest to know whether there is increased occurrence of a trait in a pedigree or other structured set of epidemiological data. In answering such questions most current methods use aggregate measures, such as relative risk, that may not relate the outcome for each individual to that individual's risk. In this paper we present a simple method, and its computational algorithm, to overcome this limitation. This new method also permits one to identify high-risk families or subsets of a collection of data, which is not always possible using other approaches. In a study of cancer risk among relatives of retinoblastoma patients, by applying this new method it was found that 11 of 33 families each obtained through a unilateral retinoblastoma patient are at statistically high risk of cancer at all sites combined, while there are 15 of 47 such families obtained through a bilaterally affected proband. These results are unlikely to have occurred by chance, indicating an overall excess risk in the ancestors of these retinoblastoma cases. The proposed test procedure does not specify the cause of elevated risk; however, a method is proposed that provides some indication regarding possible causal mechanisms under some circumstances.

Biometry↗
PubMed1984

Detection of nonrandom association of alleles from the distribution of the number of heterozygous loci in a sample.

The distribution of the number of heterozygous loci in two randomly chosen gametes or in a random diploid zygote provides information regarding the nonrandom association of alleles among different genetic loci. Two alternative statistics may be employed for detection of nonrandom association of genes of different loci when observations are made on these distributions: observed variance of the number of heterozygous loci (s2k) and a goodness-of-fit criterion (X2) to contrast the observed distribution with that expected under the hypothesis of random association of genes. It is shown, by simulation, that s2k is statistically more efficient than X2 to detect a given extent of nonrandom association. Asymptotic normality of s2k is justified, and X2 is shown to follow a chi-square (chi 2) distribution with partial loss of degrees of freedom arising because of estimation of parameters from the marginal gene frequency data. Whenever direct evaluations of linkage disequilibrium values are possible, tests based on maximum likelihood estimators of linkage disequilibria require a smaller sample size (number of zygotes or gametes) to detect a given level of nonrandom association in comparison with that required if such tests are conducted on the basis of s2k. Summarization of multilocus genotype (or haplotype) data, into the different number of heterozygous loci classes, thus, amounts to appreciable loss of information.

Alleles↗
PubMed1984

Nonrandom sampling in human genetics: familial correlations.

In the context of human genetics, sampling is often nonrandom in that pedigrees are frequently selected by virtue of their having at least one affected individual. For quantitative traits, it may be that the proband is selected because of a phenotypic value above some predetermined cut-point; this will also be true for diseases defined by a cut-point above which individuals are said to be affected (e.g. diabetes, hypertension, and obesity). Relatively little attention has been given to the implications of these forms of nonrandom sampling. In this paper, we show that the biases introduced by such sampling are sufficient to lead to erroneous model specification and biased parameter estimates in path analysis. Existing methodologies used to correct for such sampling (e.g., elimination of proband or regression techniques) also result in similar bias in estimation and model fitting. Thus, it is possible to make inferences which do not reflect underlying biology, but are artifacts of the sampling design. As a consequence, method-of-moment estimators are developed for means, variances, and correlations under such sampling. Simulation results are used to demonstrate the superiority of this method over alternate strategies.

Biometry↗
PubMed1984

Cancer mortality in relatives of retinoblastoma patients.

The risk of other cancers in relatives of retinoblastoma (RTB) patients was determined by a survey of the mortality experience of siblings, parents, parental siblings, and grandparents of all U.S. or Canadian RTB patients referred to The University of Texas M.D. Anderson Hospital and Tumor Institute between 1944 and 1980. Expected mortality was ascertained by the application of age-, sex-, race-, and calendar year-specific U.S. mortality rates to the observed person-years. Among 607 relatives of 33 unilateral-sporadic RTB probands, no excess in cancer deaths was observed (observed/expected = 18/22). Among 733 relatives of 47 bilateral-familial RTB probands, a slight excess in cancer deaths was observed (41/31). A significant excess in cancer deaths was occurred in relatives under age 55 years (18/9) and in fathers (7/1) of the bilateral RTB probands. To determine whether the cancer excess was related to some unique allele associated with second tumors in RTB survivors, the cancer mortality of 203 relatives of the 14 RTB patients with second tumors was examined, and no excess was observed (11/11). To determine whether the excess might be attributable to an unexpressed RTB gene or precursor, the mortality experience was examined in 6 kindreds in which parents, unaffected by RTB, had more than 1 child with RTB. Among these 72 relatives a significant excess in cancer deaths was observed (8/2). The findings demonstrate a modest overall cancer excess in relatives of hereditary RTB patients and suggest it may be attributable to an unexpressed RTB gene or precursor in a small number of kindreds. Mechanisms for an apparent "precursor" might involve a delayed mutation, genetic mosaicism, or a submicroscopic balanced chromosomal translocation.

Adolescent↗
PubMed1984

Multistage risk models and the age pattern in familial polyposis coli.

Multistage risk models provide a close fit to most age patterns of adult-onset cancers. Such models posit that a number of events must occur before some cell in a tissue is transformed from normal to neoplastic. When an approximate version of the models has been fitted to data, this number has been estimated to be about 4-6. In fitting the same approximate model to the age pattern of onset of colon cancer in bearers of the Familial Polyposis coli (FPC) gene, several authors have found that the number of stages estimated was about two to three fewer than those for colon cancer in the general population. However, when an exact multistage model is used rather than an approximation to it, this is no longer the case: the number of stages estimated from the general population becomes too large to be compatible with what is known about carcinogenesis from laboratory experiments, and the number estimated from FPC victims is larger than that for the general population. "Inherited-hit" models of the nature of the FPC gene may be correct at the cellular level, but multistage models as commonly formulated cannot be used on data on the age-onset patterns in populations of individuals to infer such mechanisms or estimate their parameters.

Age Factors↗
PubMed1984

Heritability of quantitative variation at the group-specific component (Gc) locus.

Human group-specific component (Gc) is the plasma transport protein for vitamin D; in addition, polymorphic electrophoretic variants of Gc are found in all human populations. Because of its physiologic importance and in view of the extensive genetic variation at the Gc locus, we have determined the heritability of quantitative variation in Gc by comparing a series of monozygotic (MZ) and dizygotic (DZ) twins of known Gc genotype. The series included 31 MZ twin pairs, 13 DZ twin pairs, and 45 unrelated controls. Since Gc concentration is increased by estrogens, pregnant women and women taking oral contraceptives were excluded. We found no age-related differences in Gc concentration or differences between males and females, but the concentrations of Gc in the three electrophoretically determined genotypes were significantly different from each other. Using classical methods of heritability analysis, the overall heritability of variation in Gc concentration is approximately 70%. Heritability in males is greater than in females, probably reflecting the additional environmental effect of estrogens in women. To determine if the differences in Gc concentration between the three genotypes explain the high heritability, a new variance decomposition procedure was developed following classical methods in quantitative genetics. Application of this method suggests that 19% of the total variation in Gc concentration, combining both sexes, is due to electrophoretic differences between individuals (30% in females and 20% in males). Thus, the genetic component of variation in Gc concentration can be decomposed into a major gene component--the result of electrophoretic variation at the structural locus--and a second, unexplained, polygenic component.

Adolescent↗
PubMed1984

Variations in the length of human Y chromosome: a statistical study.

A statistical test is proposed to examine the relationship between the mean and variance of the relative length of Y chromosome (as measured by Y/A2 or Y/F indices) in various racial groups. It is shown that the variance of Y chromosome length within a population is quadratically related with its mean if the Y chromosome length variation is caused only by variations in the number of copies of repeated DNA sequences. No such relationship is observed in the available data on relative lengths of the Y chromosome in various racial groups. We thus conclude that the length polymorphism in human Y chromosome may not be solely due to variations in the amount of Y chromosome-specific repeated DNA.

Humans↗
PubMed1984

Collagen hydrolysis by a new Streptomyces species.

A soil streptomycete hydrolysed collagen extracted from bovine Achilles tendon, calf skin, carp swim bladder and rat tail tendon. Enzyme activity was highest with rat tail tendon collagen as substrate. The taxonomy of the streptomycete was studied according to internationally approved methods. Comparative studies revealed that it resembled Streptomyces humidus , S. rochei and S. distatochromogenes in some respects, but differed in many cultural and physiological characteristics. Based on these differences the organism was given a new identity as Streptomyces species A.

Achilles Tendon↗
PubMed1983

Structured exploratory data analysis (SEDA) of finger ridge-count inheritance: I. Major gene index, midparental correlation, and offspring-between-parents function in 125 south Indian families.

Fourteen dermatoglyphic traits measured on 125 Velanadu Brahmin families were analyzed for mode of inheritance using three Structured Exploratory Data Analysis (SEDA) statistics: the major gene index, the offspring between parents function, and the traditional midparental correlation coefficient. Since the traits are integer valued with restricted ranges of variation, we simulated various transmission models with discrete expression to better understand the nature of the SEDA statistics for such variables. In addition, permutation procedures were employed to aid the interpretation of the SEDA results. These analyses suggest that corresponding homologous fingers on the left and right hands exhibit similar transmission characteristics. The relationship of the parent and child total ridge-counts of the two hands separately, as well as their combined total, virtually simulate complete Galtonian blending inheritance. Results for the individual digital ridge-counts as well as the pattern-intensity-index variable also suggest a multifactorial mode of transmission or possibly one involving several genes.

Dermatoglyphics↗
PubMed1983

Structured exploratory data analysis (SEDA) of finger ridge-count inheritance: II. Association arrays in parent-offspring and sib-sib pairs.

Familial similarity of the dermatoglyphic trait values of finger ridge-count scores and pattern intensity index is examined for 125 nuclear families from the Velanadu Brahmin population of Southern India by the method of association arrays. This methodology assesses parent-offspring and sibship similarity through a collection of measures of dependence that is sensitive to a variety of nonlinear trends and stochastic relationships between trait values. The method is used in conjunction with various weights to determine the relationship between family size and the level and form of dependence. These analyses reveal that siblings are most strongly associated for ridge-counts of the middle digit and less associated for the thumb and fifth digit ridge-counts. Further, sibship similarity for ridge-counts increases with family size for the thumb and fifth digit but remains relatively constant over all family sizes for the middle finger. Family size effects are also observed for total ridge-counts of the left hand, right hand, and both hands combined, and for the pattern intensity index. These effects of family size may be due to the most pronounced changes occurring in the amniotic environment between the first and second pregnancy, which are most strongly manifested in the sibship associations of smaller families.

Dermatoglyphics↗
PubMed1983

Paternity exclusion and the paternity index for two linked loci.

Algebraic expressions for the average exclusion frequency and the paternity index are derived for two linked loci, each with two alleles segregating in a population. The effects of recombination and gametic disequilibrium on these two statistics are discussed. As long as recombination is known to exist, the average exclusion frequency is similar for different recombination fractions. The paternity index, on the other hand, depends very much on both the recombination fraction and gametic disequilibrium. The effects of multiple alleles and dominance on these statistics are also briefly discussed.

Adult↗
PubMed1983

Differences in the relative distribution of human gene diversity between electrophoretic and red and white cell antigen loci.

Gene frequency data for 25 loci (2 HLA loci, 9 blood group loci, and 14 electrophoretically detectable loci) were collected from the literature of 18 human populations from all over the world. The data were subjected to a hierarchical gene diversity analysis to provide an estimate of the relative distribution of genetic variation between and within populations and population groups for different types of loci. Two different ways of grouping the populations, i.e., according to anthropological criteria and to a cluster analysis based on gene frequency data, gave essentially the same results. For all loci combined approximately 86% of total gene diversity was found within populations, 3% was associated with differences between populations within groups, and 11% related to group differences. These results are very similar to those obtained in previous studies based on fewer loci and different sets of populations. The distribution of genetic variation is different for different types of loci. The HLA loci give a picture very similar to that of the electrophoretic loci while the blood group loci have a substantially larger fraction of the total gene diversity distributed between populations or population groups.

Blood Group Antigens↗
PubMed1983

Path analysis in genetic epidemiology: a critique.

Path analysis, a form of general linear structural equation models, is used in studies of human genetics data to discern genetic, environmental, and cultural factors contributing to familial resemblance. It postulates a set of linear and additive parametric relationships between phenotypes and genetic and cultural variables and then essentially uses the assumption of multivariate normality to estimate and perform tests of hypothesis on parameters. Such an approach has been advocated for the analysis of genetic epidemiological data by D. C. Rao, N. Morton, C. R. Cloninger, L. J. Eaves, and W. E. Nance, among others. This paper reviews and evaluates the formulations, assumptions, methodological procedures, interpretations, and applications of path analysis. To give perspective, we begin with a discussion of path analysis as it occurs in the form of general linear causal models in several disciplines of the social sciences. Several specific path analysis models applied to lipoprotein concentrations, IQ, and twin data are then reviewed to keep the presentation self-contained. The bulk of the critical discussion that follows is directed toward the following four facets of path analysis: (1) coherence of model specification and applicability to data; (2) plausibility of modeling assumptions; (3) interpretability and utility of the model; and (4) validity of statistical and computational procedures. In the concluding section, a brief discussion of the problem of appropriate model selection is presented, followed by a number of suggestions of essentially model-free alternative methods of use in the treatment of complex structured data such as occurs in genetic epidemiology.

Asian↗