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Biomedical subjects

G Barbujani

Publications and source records attributed to G Barbujani.

70 records · Page 4Linked to original sources
PubMed1987

Autocorrelation of gene frequencies under isolation by distance.

Spatial autocorrelation statistics are used for description of geographic variation of gene frequencies, but the relationship of these indices with the parameters describing the genetic structure of populations is not established. A simple relation is derived here between kinship coefficient and a measure of spatial autocorrelation, Moran's I. The autocorrelation coefficient of gene frequencies at a given distance is a direct function of the kinship at that distance, and an inverse function of the standardized gene frequency variance, Fst. Under isolation by distance, the expected values of Moran's I for any allele may be calculated by means of Malécot-Morton function, which predicts an exponential decline of genetic similarity in space. This allows comparison of observed gene frequency patterns with the patterns that should be caused by interaction of short range migration and random genetic drift.

Alleles↗
PubMed1987

Biological performance in beta-thal heterozygotes and normals: results of a longitudinal comparison in a former malarial environment.

Families of beta-thal heterozygotes and of normals studied in 1956 by Silvestroni and Bianco in the small town of Berra near Ferrara were studied again in 1981-85. It was possible to compare mortality, fertility, and migration, in the two groups of heterozygotes and normals after the lapse of one generation. At the power of resolution of the sample available and of the methods used, no difference was visible. However, it was possible to establish the upper limits of the differences in average age at death and in average fertility at the 5% level of significance.

Age Factors↗
PubMed1987

Diversity of some gene frequencies in European and Asian populations. III. Spatial correlogram analysis.

The gene frequencies at eight loci in some European and Asian human populations have been subjected to spatial autocorrelation analysis, using Geary's c coefficient. Contrary to what is expected for markers affected only by gene flow and genetic drift, the spatial correlograms show distinct modes of gene frequency variation: there are significant clinal patterns (at the GLO and ESD loci), significant non-clinal patterns (AK, ADA, 6-PGD and GPT) and marginally significant patterns (PGP and SOD). Any hypothesis on the evolution of these polymorphisms should account for the observed heterogeneity of their geographical distributions.

Asia↗
PubMed1987

Diversity of some gene frequencies in European and Asian populations. II. Fit of an isolation by distance model.

Six enzyme polymorphisms have been studied in European and Asian populations, using kinship as an index of genetic differentiation. Four clusters of populations are apparent, corresponding to four geographical regions. The differences between such groups account for a large fraction of genetic diversity, while minor differences are apparent between populations belonging to the same continent or subcontinent. The kinship as bioassayed from three loci (GLO, ESD, 6-PGD) correlates significantly with space, showing an exponential decline with the increase of distance between populations.

Asia↗
PubMed1986

Surveillance of birth defects: the Multicommunity Sets Technique tested by computer simulation.

Using a computer simulation for a series of births subject to various congenital malformations, the surveillance performance of the Multicommunity Sets Technique (MST) was compared to that of the Cumulative Sum Technique (CUSUM). Increases in malformation frequencies were simulated in (i) 6 out of 6 centres and (ii) only 3 out of 6 centres. MST was neither more sensitive nor more specific than CUSUM, and signalled increases with greater delay. One type of CUSUM procedure showed to accumulate more false alarms than MST in long periods of surveillance at the baseline malformation rate. The advantage of CUSUM was also shown for a single malformation with a very low baseline incidence, which according to Chen et al. (1983) should have been particularly suitable for MST surveillance.

Computer Simulation↗
PubMed1986

Torus palatinus: a segregation analysis.

Segregation analysis of 99 sibships in 2 samples from Venezuela and Japan indicates that a torus palatinus is inherited in simple dominant fashion. The gene shows variable expressivity and penetrance close to 85%, without significant heterogeneity between the populations considered. No evidence of sporadic cases has been found.

Gene Frequency↗
PubMed1985

A two-step test for the heterogeneity of Fst values at different loci.

Under genetic drift and in the absence of selection, the Fst values are expected to be equal at all loci, and heterogeneity among such values is considered as an evidence for different systematic pressures affecting the different genetic systems considered. A two-step test is here proposed. Fst values at various loci are classified into two nonarbitrary groups through the analysis of the association between pairs of genetic and environmental variables; the heterogeneity is then assessed by Wilcoxon's two-sample test. Estimation of the theoretical variance of Fst, which causes major shortcomings in the test proposed by Lewontin and Krakauer in 1973, is thus avoided.

Chromosome Mapping↗
PubMed1985

Segregation analysis of hemophilia A and B.

We analyzed a sample of 1,485 families with hemophilia A and B and with unknown diagnosis. The frequency of sporadic cases was estimated to be .166 and .078 for the two types of hemophilia, respectively. The sex ratio of mutation rates did not differ significantly from unity. The average age of maternal grandfathers of probands at birth of mothers with a single child, affected by hemophilia B, and of maternal grandfathers of probands at birth of mothers with more than one child affected by hemophilia B, was higher than the age in appropriate control groups.

Age Factors↗
PubMed1984

Duchenne muscular dystrophy. Frequency of sporadic cases.

A segregation analysis on 135 Duchenne families from Venetia (Italy) suggests that the proportion of sporadic cases might be less than expected. Support for this view is also given by an analysis of a pooled sample including 284 additional sibships from comparable studies published previously. Several hypotheses were tested: the maximum likelihood was obtained for a segregation frequency p = 0.46 and for a proportion of sporadic cases x = 0.227 +/- 0.048.

Gene Frequency↗
PubMed1984

Beta-thalassemia in the Po Delta: selection, geography, and population structure.

The allele frequencies for beta-thalassemia for 51 localities in the province of Rovigo, and in 25 localities in the province of Ferrara, were studied. It was observed that in the province of Ferrara there is a significant cline of frequencies; these decrease from the coast of the Adriatic Sea toward the west. No such gradient was visible in Rovigo. It was advanced, also on the basis of geography documented by ancient maps, that in the province of Rovigo there were multiple foci of selection for the thalassemia gene, and that in the province of Ferrara selection was stronger in the Oriental part of the area. Examination of the isolation by distance model with these data showed that the Malécot-Morton model fits for the Ferrara data and geography, whereas it does not for Rovigo.

Alleles↗
PubMed1983

A new rare variant of the glyoxalase I system of the red cell: GLO-Sicily.

A fast variant of the red cell enzyme glyoxalase I was identified in a sample of 663 persons from Eastern Sicily; the allele was designated GLOSi. The gene frequencies for the common alleles GLO1 and GLO2 are not different from those observed in other southern Italian populations, and are in agreement with the hypothesis of a westward gene flow from Asia.

Alleles↗
PubMedDate not supplied

Comparison of two statistical techniques for the surveillance of birth defects through a Monte Carlo simulation.

In a multi-hospital surveillance system for detecting increases in congenital malformation rates, the performance of the set technique applied individually to hospitals and of the cumulative sum (Cusum) technique applied to the aggregate of hospitals has been compared using a Monte Carlo method. The Cusum technique appears to be both more sensitive to real increases and less likely to issue false alarms.

Computers↗
PubMedDate not supplied

A cline for glyoxalase I allele frequencies in Italy.

A gradient of glyoxalase I allele frequencies is described in Italian populations. The association between longitude and allele frequency is assessed through simple and multiple correlation, and gene flow is suggested as a major factor in the origin of such a pattern.

Alleles↗
PubMedDate not supplied

Surnames in Ferrara: distribution, isonymy and levels of inbreeding.

The distributions of surnames in populations of small and large towns are almost exactly linearized by a log-log transformation. This indicates probable fit of genetic models to most such distributions, even when the number of surnames is very large. Genetic parameters can then be conveniently calculated from surname distributions. It was found that inbreeding indicators calculated from isonymy are negatively correlated with the size of the towns from which the names were extracted. It was also found that the levels of inbreeding at present observed in Ferrara have little effect on the frequency of homozygotes for the beta-thalassaemia gene.

Consanguinity↗