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S Abrahamson

Publications and source records attributed to S Abrahamson.

At least 19 recordsLinked to original sources
PubMed1990

Risk estimates: past, present, and future.

Risk estimates for genetic disease developed over the past 30 y have been reviewed. The influence of dose rate and nonlinear dose-response curves on low dose estimates are discussed, and a reevaluation of doubling dose from acute irradiation is presented. The issue of differential sensitivity between human and mouse data are discussed with respect to the lack of an observable induced mutation rate in the offspring of A-bomb survivors. It is concluded that the "presumably" more sensitive mouse-derived risk estimates would not predict a significant increase in F1 abnormalities in humans. Therefore, it may be premature to accept the interpretation that man is less radiosensitive than the mouse.

Animals↗
PubMed1984

Chromosome mutation tests for mutagenesis in Drosophila melanogaster. A report of the U.S. Environmental Protection Agency Gene-Tox Program.

The term 'chromosome mutations' was chosen and defined for this review to refer to alterations of chromosome structure (reciprocal, heritable translocations), of chromosome number (loss or gain of a whole chromosome), or of chromosome content (loss or gain of a part of a chromosome). Chromosome mutations may result from chromosome breakage (clastogenesis) and its consequences or from disruption of chromosome behavior during cell division (nondisjunction). State-of-the-art protocols are outlined to test for heritable translocations, for whole-or partial chromosome loss (clastogenesis), and for whole chromosome loss or gain (nondisjunction). The literature up to 1980 was reviewed and 106 papers were selected for the evaluation of 116 chemicals for one or more chromosome mutation end points. The criteria used for acceptance of data from the literature were not stringent, as most of this work was done some time ago and for purposes other than testing. The main criterion was that germ cell stage sampling was correct. For the evaluation of the accepted data, numerical requirements were set up, using as a guide the control data from all the papers. Compounds were classified, when possible, as mutagenic (+) or nonmutagenic (-). Those not classifiable, usually due to insufficient numbers of chromosomes tested, were listed as inconclusive (inc). Of 61 compounds tested for heritable translocations, 27 were positive, 8 were negative, and 26 were inconclusive. Of the 35 with conclusive data, only 21 also have definitive carcinogenesis classifications (all positive). Of these, 19 were deemed mutagenic, which gives agreement of 90.5%. Of the 76 compounds tested for clastogenesis by the chromosome loss test, 26 were positive, 13 were negative, and 37 were inconclusive. Of the 39 with conclusive data, only 20 also have definitive carcinogenesis classifications. 15 of the 19 carcinogens were positive. Four of the carcinogens were negative and 1 noncarcinogen was positive, for an overall agreement of 75%. Of 44 compounds tested for nondisjunction, 15 were positive, 13 were negative, 16 were inconclusive. Of the 28 compounds with conclusive data, only 9 have definitive carcinogenesis classifications (all positive). Five of these were deemed negative and agreement was only 44%. It should be noted that these data do not fairly represent these short-term tests as conducted with current protocols. A more equitable comparison could be achieved with planned experiments that include the sex-linked recessive lethal (SLRL) test in the comparison.

Aneuploidy↗
PubMed1983

Germ cell comparative Drosophila mutagenesis: sensitivity and mutation pattern in chemically treated stem cells.

Mutagenesis studies on Drosophila oogonial cells with methylnitrosourea, dimethylnitrosamine, and diethylnitrosamine revealed unexpectedly high rates of sex-linked recessive lethals relative to other male and female germ cell stages. Indeed, the oogonial mutation rates with chemicals are higher than with massive X-ray or neutron exposures of oogonia. Analysis of the distribution of lethals per treated female suggests most of the mutations recovered are of independent origin, with very small levels of clustering of identical mutations. In the male stem cell population (spermatogonia) on the other hand, the distribution of lethals is primarily nonrandom and highly clustered. The nature of the mutational endpoint and the different pattern of germ cell development in the two sexes are the probable causes of this difference. The oogonial sensitivity to chemical mutagens may have important bearing on strategies for assessing human hazard.

Animals↗
PubMed1983

The sex-linked recessive lethal test for mutagenesis in Drosophila melanogaster. A report of the U.S. Environmental Protection Agency Gene-Tox Program.

The test for sex-linked recessive lethals (SLRL) in Drosophila melanogaster has been used to detect induced mutations since 1927. The advantage of the test for both screening and hazard evaluation is its objectivity in testing for transmissible mutations in the germ cells of a eukaryote. Statistical criteria for both positive and negative mutagenicity at the highest concentration tested under a particular exposure condition were developed by the Work Group, and a recommended protocol for future testing was agreed upon. For 421 compounds there were sufficient data available in the literature for analysis; 198 compounds were found to be positive and 46 negative at the highest concentration tested. Most experiments had been done for objectives of pure research rather than for deliberately screening for mutagenicity, although many of the 421 chemicals were selected for testing because of suspected mutagenicity. Therefore, the statement of 198 positive and 46 negative should not be taken as an example of the proportion of mutagens in the environment. In three sets of experiments with D. melanogaster that were done specifically for screening, one involving 40 compounds for the Environmental Protection Agency (EPA), the others involving 13 for the Food and Drug Administration (FDA), only 6 mutagens were discovered. After completion of the classification of compounds according to their response in the SLRL test, the compounds were classified as to their carcinogenic response according to the list of Griesemer and Cueto (1980). There were 62 compounds that could be classified as positive or negative for both carcinogenesis and mutagenesis. Of the 62 compounds, there was agreement between the carcinogenesis and mutagenesis classification in 56 (50 positive and 6 negative), or 90% would have been correctly classified as to carcinogenesis from only the SLRL test. Because of inadequate sample size, 177 compounds could not be classified as positive or negative according to the statistical criteria established by the Work Group. This large number of inadequately tested compounds reflects the fact that many of the experiments were not done for screening. Further work is needed on the compounds with inadequate sample size.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1980

How many loci on the X-chromosome of Drosophila melanogaster can mutate to recessive lethals?

The sensitivity of the sex-linked recessive lethal test is due to the fact that a very large number of loci are included i the mutation study. From extensive studies on the spontaneous sex-linked recessive lethal frequency and spontaneous specific locus mutation rates, it is possible to derive an estimate of the number of loci included in the recessive lethal test. The average number derived from three estimates on male and female germ cells is 563 loci. A second independent approach derives from published data which analyzed short regions of he genome and the proportion of loci within these regions which mutate to lethality. This analysis suggests that 830 loci are potentially lethal mutables. We describe the reasons for concluding that 600 to 800 loci of the approximately 1,000 loci on the X-chromosome are involved in the X-linked recessive lethal test.

Animals↗
PubMed1979

A national study of internal medicine and its specialties: I. An overview of the practice of internal medicine.

A nationwide study of 24 medical and surgical specialties has been conducted by the University of Southern California School of Medicine, Division of Research in Medical Education. This article is the first in a series reporting findings for general internal medicine and 10 subspecialties of internal medicine. Populations for these 11 specialties are defined and enumerated, and the specialties are compared in terms of demographic and geographic distribution. Practice comparisons are presented based on characteristics such as workload, allocation of professional time, location of encounters with patients, distribution of primary problem diagnoses, and projections of annual patient encounters. Forthcoming specialty-specific articles will present highly detailed information for general internal medicine and for the subspecialties of cardiology, gastroenterology, pulmonary disease, allergy, hematology, endocrinology, nephrology, medical oncology, rheumatology, and infectious diseases.

California↗
PubMed1978

A national study of medical and surgical specialties. II. Description of the survey instrument.

The survey instrument used in the national study of physician activities conducted by the University of Southern California, Division of Research in Medical Education, is a log-diary in which physicians kept a record of their actual professional activities. The log-diary focused on use of physician time and patient encounters and employed numerical coding of activities and patient encounters in a highly structured format. Compared with instruments used in similar studies, this log-diary appears to gather a greater breadth and depth of information about physician practice patterns.

California↗
PubMed1978

A national study of medical and surgical specialties. I. Background purpose, and methodology.

The University of Southern California is conducting a national survey of physicians involving the collection and analysis of detailed data on the activities and practice characteristics of generalists, medical specialists, and surgical specialists of different types. This is the first of a series of reports on the survey and provides an overview of the survey's background, purposes, and general research methods. Basic features of the research methods include the development of a survey instrument capable of obtaining different types of practice data from physicians in most specialties and practice arrangements, the sampling of physician population to ensure that sufficient data are obtained from physicians in most specialties and practice arrangements, and the creation and application of a scheme for classifying patient-care services provided by physicians along dimensions related to primary care.

Family Practice↗
PubMed1978

Diseases of the curriculum.

During the past 20 years the author has visited almost half of all the American medical schools, usually as a consultant in matters of curriculum and instruction. Certain recurring curriculum problems have emerged and have been described as "diseases of the curriculum." To be exact, this article includes nine such entities. In addition to the naming of these nine curriculum conditions, there is ample illustrative material to ensure that each curriculum disease is fully explained--although the basic sciences supporting the study of education as a discipline are not advanced enough to allow fuller understanding of the disease processes. There is speculation, however, that even being able to name and describe these disturbances of normal curriculum development might be of help in solving some of our more serious curriculum problems.

Communication↗