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Biomedical subjects

B Devlin

Publications and source records attributed to B Devlin.

At least 73 records · Page 4Linked to original sources
PubMed1993

Genotypic divergence precedes clinical dissemination in a case of synchronous bilateral B-cell malignant lymphoma of the testes.

Malignant lymphoma of the testis occurs bilaterally more often than any other tumor type. We report the case of a 62-year-old man who presented with synchronous, bilateral, testicular malignant lymphomas without clinical or radiologic evidence of extratesticular disease. The patient received no therapy other than bilateral orchiectomy and subsequently developed widespread disease 6 months later. Southern blot DNA analysis was performed on the initial orchiectomy samples for immunoglobulin (Ig) gene rearrangements. These genotypic analyses showed different clonal rearrangements in the Ig heavy chain JH region but identical clonal rearrangements in the Ig light chain C Kappa region. To our knowledge this is the first genotypic demonstration of a common clonal origin in synchronous, bilateral, testicular malignant lymphomas. We interpret these findings as molecular evidence that the patient's malignant lymphoma was already disseminated at initial presentation, although it was clinically undetectable at that time.

Antigens, CD↗
PubMed1993

Communicating the diagnosis of lung cancer.

In order to assess their reaction to the information given, 50 patients underwent a semi-structured interview with a social worker within 1 week of having been told the diagnosis of lung cancer. There were 32 men and 18 women with a mean age of 63 (range 38-82) years. Thirty-eight (76%) belonged to Registrar General social class IV or V, and 45 (90%) had left school at the age of 15 years. Two patients were unaware of the diagnosis despite having been told that they had lung cancer. Two patients would have preferred not to have been told the diagnosis and two were unsure, while 46 (92%) felt that telling them the diagnosis truthfully had been correct. No patient felt that they had been given too much information, but 13 (26%) indicated a lack of information about prognosis. Despite being told 'bad news', 31 (62%) felt more reassured after their interview with the doctor, 5 (10%) felt less reassured, and 14 (28%) were uncertain. Twenty-one (42%) patients were experiencing a sense of guilt or regret at having smoked. Many patients had concerns about specific symptoms which they expected to suffer. In general, patients wanted to be told their diagnosis truthfully and required a high level of information. Many patients felt reassured by the discussion of such details.

Adult↗
PubMed1993

Forensic inference from genetic markers.

This review provides an overview of forensic inference from genetic markers. Because the judge and jurors are charged with decision-making, the forensic expert's job is to provide a useful summary of the evidence to the court. Hence, this review focuses on the likelihood ratio as a means of summarizing the genetic data for either criminal or civil cases. The properties of the genetic markers frequently used in today's court cases, those being VNTR loci, are discussed in detail. Unlike traditional markers, the data from VNTR loci are complicated because current molecular methods generate data that follow a finite mixture distribution. Critical ancillary issues are also covered, though not in detail.

Bayes Theorem↗
PubMed1993

Population genetics of the HRAS1 minisatellite locus.

Several years ago it was reported that rare HRAS1 VNTR alleles occurred more frequently in U.S. Caucasian cancer patients than in unaffected controls. Such an association, in theory, could be caused by undetected population heterogeneity. Also, in a study clearly relevant to this issue, it was recently reported that significant deviations from Hardy-Weinberg equilibrium exist at this locus in a sample of U.S. Caucasians. These considerations motivate our population genetic analysis of the HRAS1 locus. From published studies of the HRAS1 VNTR locus, which classified alleles into types, we found only small differences in the allele frequency distributions of samples from various European nations, although there were larger differences among ethnic groups (African American, Caucasian, and Oriental). In an analysis of variation of rare-allele frequencies among samples from four European nations, most of the variance was attributable to molecular methodology, and very samples from four European nations, most of the variance was attributable to molecular methodology, and very little of the variance was accounted for by nationality. In addition, we showed that mixture of European subpopulations should result in only minor deviations from expected genotype proportions in a Caucasian database and demonstrated that there was no significant deviation from Hardy-Weinberg equilibrium in our HRAS1 data.

Alleles↗
PubMed1993

Physical properties of VNTR data, and their impact on a test of allelic independence.

In this article we describe the physical properties of VNTR data, as well as their effects on the two-dimensional distribution of fragment pairs. Tests of independence of alleles at a locus may confound those physical properties with allele independence. A recently proposed test by Geisser and Johnson is an example. We show that alleles can be strictly independent, yet the proposed test suggests large violations of allele independence because it is sensitive to well-known electrophoretic phenomena.

Alleles↗
PubMed1992

On the probability of matching DNA fingerprints.

Forensic scientists commonly assume that DNA fingerprint patterns are infrequent in the general population and that genotypes are independent across loci. To test these assumptions, the number of matching DNA patterns in two large databases from the Federal Bureau of Investigation (FBI) and from Lifecodes was determined. No deviation from independence across loci in either database was apparent. For the Lifecodes database, the probability of a three-locus match ranges from 1 in 6,233 in Caucasians to 1 in 119,889 in Blacks. When considering all trios of five loci in the FBI database, there was only a single match observed out of more than 7.6 million comparisons. If independence is assumed, the probability of a five-locus match ranged from 1.32 x 10(-12) in Southeast Hispanics to 5.59 x 10(-14) in Blacks, implying that the minimum number of possible patterns for each ethnic group is several orders of magnitude greater than their corresponding population sizes in the United States. The most common five-locus pattern can have a frequency no greater than about 10(-6). Hence, individual five-locus DNA profiles are extremely uncommon, if not unique.

Black People↗
PubMed1992

Ethnic differentiation at VNTR loci, with special reference to forensic applications.

Allele-rich VNTR loci provide valuable information for forensic inference. Interpretation of this information is complicated by measurement error, which renders discrete alleles difficult to distinguish. Two methods have been used to circumvent this difficulty--i.e., binning methods and direct evaluation of allele frequencies, the latter achieved by modeling the data as a mixture distribution. We use this modeling approach to estimate the allele frequency distributions for two loci--D17S79 and D2S44--for black, Caucasian, and Hispanic samples from the Lifecodes and FBI data bases. The data bases are differentiated by the restriction enzyme used: PstI (Lifecodes) and HaeIII (FBI). Our results show that alleles common in one ethnic group are almost always common in all ethnic groups, and likewise for rare alleles; this pattern holds for both loci. Gene diversity, or heterozygosity, measured as one minus the sum of the squared allele frequencies, is greater for D2S44 than for D17S79, in both data bases. The average gene diversity across ethnic groups when PstI (HaeIII) is used is .918 (.918) for D17S79 and is .985 (.983) for D2S44. The variance in gene diversity among ethnic groups is greater for D17S79 than for D2S44. The number of alleles, like the gene diversity, is greater for D2S44 than for D17S79. The mean numbers of alleles across ethnic groups, estimated from the PstI (HaeIII) data, are 40.25 (41.5) for D17S79 and 104 (103) for D2S44. The number of alleles is correlated with sample size. We use the estimated allele frequency distributions for each ethnic group to explore the effects of unwittingly mixing populations and thereby violating independence assumptions. We show that, even in extreme cases of mixture, the estimated genotype probabilities are good estimates of the true probabilities, contradicting recent claims. Because the binning methods currently used for forensic inference show even less differentiation among ethnic groups, we conclude that mixture has little or no impact on the use of VNTR loci for forensics.

Alleles↗
PubMed1992

A note on Hardy-Weinberg equilibrium of VNTR data by using the Federal Bureau of Investigation's fixed-bin method.

To fully utilize the information of VNTR data for forensic inference, the probability of observing the matching suspect and evidentiary profile in a reference population is estimated, usually by assuming independence of alleles within and between loci. This assumption has been challenged on the basis of the observation that there is frequently an excess of single-band phenotypes (SBP) in forensic data bases, which could indicate lack of independence. Nevertheless, another explanation is that the excess SBP are artifacts of laboratory methods. In this report we examine the excess of SBP for three VNTR loci studied by the FBI (D17S79 and D2S44, for blacks, and D14S13, for Caucasians). The FBI claims that the excess is due to the effect of null alleles; the null alleles are suspected to be too small to be detected. We estimate the frequency of null alleles for two loci (D17S79 and D14S13) by comparing, for these loci, the data from the FBI data base and the data from the Lifecodes data base. These comparisons yield information on small fragments because Lifecodes uses the restriction enzyme PstI, which yields larger fragments than does HaeIII, which the FBI uses. For D17S79 in blacks, we estimate a null allele frequency of 4.4%, and, for D14S13 in Caucasians, we estimate a frequency of 3.0%. The null-allele frequency for D2S44 in blacks is derived similarly, again being based on analyses of DNA cut with HaeIII and PstI; our estimate of the null-allele frequency for this locus is 1.5%.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗
PubMed1991

Estimation of allele frequencies for VNTR loci.

VNTR loci provide valuable information for a number of fields of study involving human genetics, ranging from forensics (DNA fingerprinting and paternity testing) to linkage analysis and population genetics. Alleles of a VNTR locus are simply fragments obtained from a particular portion of the DNA molecule and are defined in terms of their length. The essential element of a VNTR fragment is the repeat, which is a short sequence of basepairs. The core of the fragment is composed of a variable number of identical repeats that are linked in tandem. A sample of fragments from a population of individuals exhibits substantial variation in length because of variation in the number of repeats. Each distinct fragment length defines an allele, but any given fragment is measured with error. Therefore the observed distribution of fragment lengths is not discrete but is continuous, and determination of distinct allele classes is not straightforward. A mixture model is the natural statistical method for estimating the allele frequencies of VNTR loci. In this article we develop nonparametric methods for obtaining the distribution of allele sizes and estimates of their frequencies. Methods for obtaining maximum-likelihood estimates are developed. In addition, we suggest an empirical Bayes method to improve the maximum-likelihood estimates of the gene frequencies; the empirical Bayes procedure effects a local smoothing. The latter method works particularly well when measurement error is large relative to the repeat size, because the estimated distribution of allele frequencies when maximum likelihood is used is unreliable because of an alternating pattern of over- and underestimation. We define alleles and estimate the allele frequencies for two VNTR loci from the human genome (D17S79 and D2S44), from data obtained from Lifecodes, Inc.

Alleles↗
PubMed1990

No excess of homozygosity at loci used for DNA fingerprinting.

Variable number of tandem repeat (VNTR) loci are extremely valuable for the forensic technique known as DNA fingerprinting because of their hypervariability. Nevertheless, the use of these loci in forensics has been controversial. One criticism of DNA fingerprinting is that the VNTR loci used for the "fingerprints" violate the assumption of Hardy-Weinberg equilibrium (H-W), making it difficult to calculate the probability of observing a genotype in the population. If one can assume H-W, the probability of observing the pair of alleles constituting an individual's genotype can be calculated by taking the product of the alleles' frequencies in the population and multiplying by two if the alleles are different. The evidence cited against assuming H-W is homozygote excess, which is presumed to be caused by an undetected mixture of two or more populations with limited interpopulational mating and distinct allele frequencies. For most VNTR loci, measurement error makes it impossible to test these claims by standard methods. The Lifecodes database of three VNTR loci used for forensics was used to show that the claimed excess of homozygotes is not necessarily real because many heterozygotes with similar allele sizes are misclassified as homozygotes. A simple test of H-W that takes such misclassifications into account was developed to test for an overall excess or dearth of heterozygotes in the sample (the complement of homozygote dearth or excess). The application of this test to the Lifecodes database revealed that there was no consistent evidence of violation of H-W for the Caucasian, black, or Hispanic populations.

DNA↗
PubMed1989

Gene flow by pollen into small populations: Data from experimental and natural stands of wild radish.

Gene flow can have an especially strong impact on the evolution of small populations. However, empirical studies on the actual rates and patterns of gene flow into small populations are few. Thus, we sought to measure gene flow into small populations of wild radish. Raphanus sativus. We found significant differences in gene flow receipt among experimental populations and within those populations over a season. A maximum-likelihood estimate revealed that almost all of the gene flow into these synthetic populations had its origin in relatively distant (>650 m), large natural populations rather than the proximal (255-400 m), small synthetic populations. We also estimated rates of interpopulation mating from simple paternity analysis of progeny produced by seven small (ca. 50 plants) natural populations. Again, we found significant heterogeneity in gene flow receipt. Although these populations varied 10-fold in their range of isolation distances (100-1000 m), gene flow rates did not vary with distance. The magnitude of gene flow rates estimated in all but one population was great enough for gene flow to play an important role in the evolution of these small populations.

Journal Article↗
PubMed1985

Social interaction and interpersonal distance in normal and behaviorally disturbed boys.

Frequency of social interaction and interpersonal distance of 24 normal and 24 behaviorally disturbed white, preadolescent boys were examined. Each child's behavior was analyzed from videotapes that were recorded during four 60-min sessions, during which time the child played with the same unfamiliar peer, matched for age and emotional functioning. The results indicated that the frequency of global social interactions was a powerful discriminator between normal and disturbed boys at the older but not at the younger age levels. Proximity to peers and adults also was a powerful discriminator at both age levels. These results were discussed in relationship to the development of social skills in preadolescent children, the need to establish criteria for social competence, and the evaluation of social skills training programs from a development perspective.

Age Factors↗