Exposure to residential electric and magnetic fields and risk of childhood leukemia

The relation between exposure to electric and magnetic fields in the home, as assessed by measurements, wiring configuration, and self-reported appliance use, and risk of leukemia was investigated in a case-control study among children from birth to age 10 years in Los Angeles County, California. Cases were ascertained through a population-based tumor registry from 1980 to 1987. Controls were drawn from friends and by random digit dialing. Interviews were obtained from 232 cases and 232 controls. Available for analysis were measurements of the magnetic field in the child's bedroom over 24 hours or longer (164 cases and 144 controls), spot measurements of magnetic and electric fields (140 cases and 109 controls), and wiring configuration (219 cases and 207 controls). No clear associations between leukemia risk and measured magnetic or electric fields were seen. An association between the Denver Wertheimer-Leeper wiring configuration and childhood leukemia risk was observed (odds ratio for very high relative to very low current and underground configuration combined = 2.15, 95% confidence interval 1.08-4.28; p for trend = 0.008) and was not substantially altered by adjustment for potential confounding factors. Cases were more likely than controls to report use of several appliances that produce high electric and magnetic fields. Our results support an association between childhood leukemia risk and wiring configuration, but not direct measurements of electric and magnetic fields.

Local blood volume changes in women with pelvic congestion measured by applied potential tomography

1. Applied potential tomography is a new, non-invasive technology for observing changes in blood volume. We have used it to study 12 women with lower abdominal pain caused by pelvic congestion, and 15 control subjects. 2. A significant increase in blood volume of 1.8% was observed in the pelvis of women with congestion when changing from the supine to the erect position, and of 2.7% in the control subjects (P less than 0.0002). The difference between the groups was not significant. 3. The distribution of the area over which blood volume changes took place was significantly different between the two groups (P less than 0.002). More of the posterolateral part of the pelvis was involved in women with pelvic congestion than in the control subjects. 4. Applied potential tomography distinguishes between normal women and those having pelvic congestion with a specificity of 87% and a sensitivity of 75%.

Exonucleolytic proofreading of leading and lagging strand DNA replication errors

We have asked whether exonucleolytic proofreading occurs during simian virus 40 origin-dependent, bidirectional DNA replication in extracts of human HeLa cells. In addition, we have compared the fidelity of leading and lagging strand DNA synthesis. In a fidelity assay that scores single-base substitution errors that revert a TGA codon in the lacZ alpha gene in an M13mp vector, providing an excess of a single dNTP substrate over the other three dNTP substrates in a replication reaction generates defined, strand-specific errors. Fidelity measurements with two vectors having the origin of replication on opposite sides of the opal codon demonstrate that error rates for two different A.dCTP and T.dGTP mispairs increase when deoxyguanosine monophosphate is added to replication reaction mixtures or when the concentration of deoxynucleoside triphosphates is increased. The data suggest that exonucleolytic proofreading occurs on both strands during bidirectional replication. Measurements using the two simian virus 40 origin-containing vectors suggest that base substitution error rates are similar for replication of the leading and lagging strands.

Heteroduplex repair in extracts of human HeLa cells

A general repair process for DNA heteroduplexes has been detected in HeLa cell extracts. Using a variety of M13mp2 DNA substrates containing single-base mismatches and extra nucleotides, extensive repair is observed after incubation with HeLa cell cytoplasmic extracts and subsequent transfection of bacterial cells with the treated DNA. Most, but not all, mispairs as well as two frameshift heteroduplexes are repaired efficiently. Parallel measurements of repair in HeLa extracts and in Escherichia coli suggest that repair specificities are similar for the two systems. The presence of a nick in the molecule is required for efficient repair in HeLa cell extracts, and the strand containing the nick is the predominantly repaired strand. Mismatch-dependent DNA synthesis is observed when radiolabeled restriction fragments, produced by reaction of the extract with heteroduplex and homoduplex molecules, are compared. Specific labeling of fragments, representing a region of approximately 1,000 base pairs and containing the nick and the mismatch, is detected for the heteroduplex substrate but not the homoduplex. The repair reaction is complete after 20 min and requires added Mg2+, ATP, and an ATP-regenerating system, but not dNTPs, which are present at sufficient levels in the extract. An inhibitor of DNA polymerase beta, dideoxythimidine 5'-triphosphate, does not inhibit mismatch-specific DNA synthesis. Aphidicolin, an inhibitor of DNA polymerases alpha, delta, and epsilom, inhibits both semiconservative replication and repair synthesis in the extract. Butylphenyl-dGTP also inhibits both replicative and repair synthesis but at a concentration known to inhibit DNA polymerase alpha preferentially rather than delta or epsilon. This suggests that DNA polymerase alpha may function in mismatch repair.

A comparative trial of two walking systems for paralysed people

A trial has been performed to compare two designs of reciprocal walking orthosis for paralysed people--the hip guidance orthosis (HGO) from Oswestry, England, and the reciprocating gait orthosis (RGO) from New Orleans, USA. Eighteen male and 4 female paraplegic subjects used each orthosis for 4 months, in a crossover study. All aspects of the provision and use of the devices were monitored, and a variety of assessments were made. Fifteen subjects were able to use both orthoses, 5 were unable to use either and 2 succeeded with the HGO but not the RGO. At the end of the trial 12 subjects chose to keep the RGO, 4 the HGO, and 6 kept neither. Those choosing the RGO liked its appearance; those choosing the HGO liked the speed of donning and doffing. The RGO was about 50% more expensive to supply than the HGO.

Sequence effect on incision by (A)BC excinuclease of 4NQO adducts and UV photoproducts

Nucleotide excision repair in Escherichia coli is initiated by (A)BC excinuclease, an enzyme which incises DNA on both sides of bulky adducts and removes the damaged nucleotide as a 12-13 base long oligomer. The incision pattern of the enzyme was examined using DNA modified by 4-nitroquinoline 1-oxide (4NQO) and UV light. Similar to the cleavage pattern of UV photoproducts and other bulky adducts, the enzyme incises the 8th phosphodiester bond 5' and 5th phosphodiester bond 3' to the 4NQO-modifed base, primarily guanine. The extent of DNA damage by these agents was determined using techniques which quantitatively cleave the DNA or stop at the site of the adduct. By comparison of the intensity of gel bands created by (A)BC excinuclease and the specific cleavage at the damaged site, the efficiency of (A)BC excinuclease incision at 13 different 4NQO-induced adducts and 13 different photoproducts was determined by densitometric scanning. In general, incisions made at 4NQO-induced adducts are proportional to the extent of damage, though the efficiency of cutting throughout the sequence tested varies from 25 to 75%. Incisions made at pyrimidine dimers are less efficient than at 4NQO-adducts, ranging from 13 to 65% incision relative to modification, though most are around 50%. The two (6-4) photoproducts within the region tested are incised more efficiently than any pyrimidine dimer.

Leukemia in Utah and radioactive fallout from the Nevada test site. A case-control study

Previous studies reported an association between leukemia rates and amounts of fallout in southwestern Utah from nuclear tests (1952 to 1958), but individual radiation exposures were unavailable. Therefore, a case-control study with 1177 individuals who died of leukemia and 5330 other deaths (controls) was conducted using estimates of dose to bone marrow computed from fallout deposition rates and subjects' residence locations. A weak association between bone marrow dose and all types of leukemia, all ages, and all time periods after exposure was found. This overall trend was not statistically significant, but significant trends in excess risk were found in subgroups defined by cell type, age, and time after exposure. The greatest excess risk was found in those individuals in the high-dose group with acute leukemia who were younger than 20 years at exposure and who died before 1964. These results are consistent with previous studies and with risk estimates for other populations exposed to radiation.

A model for dose rate and duration of exposure effects in radiation carcinogenesis

Multistage models have been used to describe various features of the incidence of cancer including the shape of the age-incidence curve; the influence of age at, duration of, and time since exposure; and the synergistic effect of exposure to multiple carcinogens. However, the models require from five to seven distinct transformations that must occur in a particular sequence. The lack of experimental support for so many events suggests a simpler model involving only two mutational events with a proliferative advantage for intermediate-stage cells. Neither model easily explains the paradoxical phenomenon that protraction of low linear energy transfer (LET) radiation leads to lower risks per unit of total exposure, whereas the reverse occurs for high-LET radiation. In this paper, a three-stage model is considered that consists of two mutations at homologous sites, either or both of which might be induced by radiation, followed by activation of the transformed oncogene, which is not induced by radiation. Single-stranded lesions are potentially repairable, whereas double-stranded lesions may increase the proliferation rate. For low-LET radiation, these two mutations are more likely to occur as the result of independent transversals of a cell by separate quanta of radiation, whereas for high-LET radiation, they are more likely to occur simultaneously as the result of a single particle. The predictions of the model are illustrated for various patterns of exposure and choices of model parameters. Various tests of the proposed model are discussed.

Survival models for familial aggregation of cancer

It has recently been shown that the relative risks of the order of 2 to 4 that are frequently found for cancer among relatives of affected cases are unlikely to be explainable by shared environmental risk factors. Classical methods of epidemiological analysis are not well suited to such analysis because they assume that the outcomes of each individual are independent. Classical methods of genetic analysis, on the other hand, are limited in their handling of environmental factors and variable ages of onset. The recent development of random effects models for survival analysis, however, appears to bridge this gap. Specifically, a proportional hazards model is postulated for the effects of measured covariates and of one or more components of frailty that are unmeasured but assumed to have some common distribution and known covariance structure within each family. From these assumptions, the posterior expectation of the hazard for each individual can be derived, given the covariate value and the observed and expected disease history of the family. These are then treated as known in a standard partial likelihood analysis; this is essentially a form of expectation-maximization algorithm. However, this does not provide a valid estimate of the covariance matrix because it fails to take account of the variability in the estimates of the frailties; an alternative approach using the imputation-posterior algorithm is suggested. This paper describes extensions of this approach to multivariate frailty distributions, modifications for application to pedigree and case-control studies, some simulation results, and applications to studies of breast cancer in twins and of lung cancer in relation to family smoking habits.

Fidelity of animal cell DNA polymerases alpha and delta and of a human DNA replication complex

We are investigating the mechanisms by which mutations are produced or avoided during DNA synthesis. Using in vitro fidelity assays, we have defined the error frequency and mutational specificity of the replicative animal cell DNA polymerases (alpha and delta). With DNA polymerase alpha or the four-subunit DNA polymerase alpha-DNA primase complex, neither of which contains detectable associated exonuclease activity, the fidelity of the polymerization step is low relative to spontaneous mutation rates in vivo. DNA polymerase delta is much more accurate, partly due to proofreading by the 3'----5' exonuclease activity associated with this polymerase. These fidelity studies have been extended to the replication apparatus present in extracts of human HeLa cells. The replication complex is highly accurate, suggesting that additional fidelity components are operating in the extract during bidirectional, semiconservative replication of double-stranded DNA. Nevertheless, in highly sensitive reversion assays, base substitution errors can be readily detected at frequencies greater than the estimated rate of spontaneous mutation in vivo. This suggests that fidelity components may be missing and/or that human cells depend heavily on postreplicative repair processes to correct replication errors.

Bivariate survival models for analysis of genetic and environmental effects in twins

Classic methods in genetics for the analysis of binary attributes, based on an assumption of a "threshold" on a normally distributed latent variable called "liability," estimate the strength of genetic and environmental effects from differences in correlations between relatives of differing genetic relatedness. Two problems that are not easily addressed by these methods are the need to take the age of onset into account (particularly in chronic diseases in which incidence rates vary considerably with age and the lengths of time at risk can vary between individuals) and the desirability of incorporating measured covariates (genetic or environmental). The standard methods of cohort analysis used in epidemiology allow for both of these features, but until recently have been restricted to independent individuals. Recent developments in survival analysis have extended the widely used "proportional hazards" model of Cox by the addition of latent variable, epsilon, reflecting the shared susceptibility of related subjects because of their shared genes or shared environment. We show how this approach can be combined with more traditional models of gene-environment interaction to allow the main effects of measured genetic markers and environmental variables to be estimated, as well as the residual variance of genetic and environment and their interactions. The approaches are applied to a cohort of female twin births in Sweden from 1886 to 1958, linked with the Swedish cancer registry from 1961 to 1982.

Nested case-control and case-cohort methods of sampling from a cohort: a critical comparison

The recently developed case-cohort method of sampling from a cohort is compared with the nested case-control method. Corrected asymptotic relative efficiency results show that the case-cohort design for single "disease" outcomes offers less improvement for intervention trials for which there is no random censoring than originally suggested. Furthermore, simulation results indicate that if there is moderate random censoring or staggered entry, the case-cohort method can do substantially worse than the nested case-control method.

The role of interferon in the protection of ICR Swiss male mice by the nondiabetogenic variant of encephalomyocarditis virus against virus-induced diabetes mellitus

The production of murine diabetes mellitus by the diabetogenic variant of encephalomyocarditis virus (EMCV-D) is prevented in mice preinfected for 24 h with nondiabetogenic virus (EMCV-B). It has been suggested that the protection of the animals is due to the induction of interferon (IFN) by EMCV-B. The present study was done to investigate further the role of IFN in the protection of male ICR Swiss mice against the diabetogenic effects of EMCV-D virus. The results show that this mouse strain is protected only by viable EMCV-B given by either the i.v. or i.p. route of inoculation and that the protection is not abrogated by anti-IFN gamma-globulin. Further, the animals were not protected by either IFN-alpha, IFN- beta, or IFN- alpha/beta at concentrations shown previously to protect mice against the lethal effects of other variants of EMCV. The data provide further evidence that, in the ICR Swiss mouse, IFN does not play a major role in protecting pancreatic beta-cells against infection by EMCV-D.

Preferential DNA repair of (6-4) photoproducts in the dihydrofolate reductase gene of Chinese hamster ovary cells

We have developed a method to quantify (6-4) photoproducts in genes and other specific sequences within the genome. This approach utilizes the following two enzymes from Escherichia coli: ABC excinuclease, a versatile DNA repair enzyme which recognizes many types of lesions in DNA, and DNA photolyase, which reverts pyrimidine dimers. DNA is isolated from UV irradiated Chinese hamster ovary cells and digested with a restriction enzyme. Pyrimidine dimers, the major photoproduct produced at biological UV fluences, are then completely repaired by treatment with DNA photolyase. The photoreactivated DNA is treated with ABC excinuclease, electrophoresed in an alkaline agarose gel, transferred to a support membrane and probed for specific genomic sequences. Net incisions produced by ABC excinuclease following photoreactivation are largely due to the presence of (6-4) photoproducts. These adducts are quantitated by measuring the reduction of intensity of the full length fragments on the autoradiogram. Using this approach we have shown that (6-4) photoproducts are produced at equal frequency in the dihydrofolate reductase coding sequence and in its 3'-flanking, noncoding sequences and that the formation of (6-4) photoproducts is linear in both sequences up to a UV dose of 60 J/m2. The repair of (6-4) photoproducts in these DNA sequences was measured after a dose of 40 J/m2 over 4-, 8-, and 24-h time periods. The (6-4) photoproducts are repaired more efficiently than pyrimidine dimers in both sequences and there is preferential repair of (6-4) photoproducts in the dihydrofolate reductase gene compared with the downstream, noncoding sequences.

Tropism and histopathology of the D, B, K, and MM variants of encephalomyocarditis virus

Variants of encephalomyocarditis virus (EMCV), which are immunologically indistinguishable by hyperimmune serum, produce different disease syndromes in mice. For instance, in ICR Swiss male mice, EMCV-B produces no overt illness, EMCV-MM produces severe neurological signs followed by death, EMCV-D destroys pancreatic beta cells producing a disease syndrome resembling insulin-dependent diabetes mellitus, and EMCV-K is lethal but produces no overt signs of infection. The present study was done to determine the tissue tropism and histopathology of each of these EMCV variants in the ICR Swiss mouse model. The data show the highest concentrations in the following organs: EMCV-D in the pancreas, EMCV-B in the pancreas, EMCV-MM in the cerebrum, and EMCV-K in the medulla/brainstem. They also show that the pathological lesions produced by each variant correlate well with viral titers.

Differing attachment of diabetogenic and nondiabetogenic variants of encephalomyocarditis virus to beta-cells

The D variant of encephalomyocarditis (EMC-D) virus does not induce the production of interferon (IFN) and produces an insulin-dependent diabetes mellitus (IDDM)-like syndrome in certain mouse strains. In contrast, the B variant (EMC-B) virus, which is serologically identical to EMC-D virus, is a good inducer of IFN and is nondiabetogenic. It has been postulated that IFN may play a major role in determining the ability of these two viruses to infect pancreatic beta-cells. However, recent studies have shown that ICR Swiss and BALB/cByJ male mice are not protected by IFN against EMC-D virus-induced IDDM. Furthermore, treatment of these two strains of mice with anti-IFN gamma-globulin before infection with EMC-B virus does not result in diabetes. These observations suggest that mechanisms other than the IFN system are involved in determining the ability of the viruses to infect and destroy beta-cells. Studies were initiated to identify other mechanisms of action. In this communication, we show that up to six times more EMC-D than EMC-B virus attaches to primary beta-cells extracted from male ICR Swiss mice. This difference in ability to attach to beta-cells may account for the difference in the diabetic potential of this mouse strain.

Noise trauma in the aetiology of acoustic neuromas in men in Los Angeles County, 1978-1985

The aim of this study was to investigate whether occupational and other suggested brain tumour risk factors relate to the development of acoustic neuromas (AN) in men. Responses to interviews were compared for 86 AN patients and 86 neighbourhood controls. During the period 10 or more years before the year of diagnosis of the case, more cases than controls had a job involving exposure to extremely loud noise; noise exposure was determined by a blinded review of job histories and linkage to the National Occupational Hazards Survey data base (odds ratio (OR) = 2.2, 95% confidence interval (CI) = 1.12, 4.67). A dose-response analysis showed an increase in risk related to number of years of job exposure to extremely loud noise (P for trend = 0.02) with an OR of 13.2 (CI = 2.01, 86.98) for exposure for 20 or more years during the period up to 10 years before diagnosis. We propose that the findings in this study which identify noise as a risk factor support the hypothesis that mechanical trauma may contribute to tumorigenesis.

Surface stereophotogrammetry of thoracic kyphosis

The thoracic kyphosis angles of 16 normal individuals, 10 patients with Scheuermann's disease and 11 with adolescent idiopathic scoliosis were measured both radiographically and from Integrated Shape Imaging System (ISIS) scans obtained by surface stereophotogrammetry. There was a high correlation between the two measures. The method of kyphosis measurement from ISIS scans was then used for 30 patients with adolescent idiopathic scoliosis who underwent corrective surgery. A significant reduction in thoracic kyphosis was observed postoperatively. In another group of 28 patients managed conservatively by bracing, some hypokyphosis developed after treatment. However, we found no association between hypokyphosis and curve progression.

Diagnostic radiography as a risk factor for chronic myeloid and monocytic leukaemia (CML)

This interview study included 136 Los Angeles County residents aged 20-69 with CML diagnosed from 1979 to 1985 (cases) and 136 neighbourhood controls. During the 3-20 years before diagnosis of the case, more cases than controls had radiographic examinations of the back, gastrointestinal (GI) tract and kidneys, and cases more often had GI and back radiography on multiple occasions (odds ratio (OR) for back X-rays on five or more occasions = 12.0; P less than 0.01). Published estimates were used to assign a minimum dose to the active bone marrow for various radiographic procedures. ORs were estimated for cumulative marrow doses for each of four time periods (3-5 years, 6-10 years, 11-20 years and 3-20 years before the diagnosis of the case). The ORs for exposure to 0.99, 100-999, 1000-1999 and greater than or equal to 2000 mrad in the 3-20 years before diagnosis were 1.0, 1.4, 1.6 and 2.4 (P for highest exposure category and P for trend both less than 0.05). The association was strongest for the period 6-10 years before diagnosis, and the effects of radiation exposure during this period remained significant after consideration of other risk factors in a logistic regression analysis.

Analysis of fidelity mechanisms with eukaryotic DNA replication and repair proteins

We are investigating the mechanisms for producing or avoiding errors during DNA synthesis catalyzed by DNA replication and repair proteins purified from eukaryotic sources. Using assays that monitor the fidelity of a single round of DNA synthesis in vitro, we have defined the error frequency and mutational specificity of the four classes of animal cell DNA polymerases (alpha, beta, delta, gamma), and the fidelity of an SV40 origin-dependent DNA replication complex in extracts of HeLa cells.

Personal and family history of lung disease as risk factors for adenocarcinoma of the lung

To identify risk factors for adenocarcinoma of the lung, a population-based case-control study of 336 female cancers of this cell type and an equal number of neighborhood controls was conducted between 1983 and 1986. After adjusting for personal smoking, personal and family histories of lung disease emerged as additional risk factors. A personal history of any lung disease was associated with a 40% increase in risk [smoking adjusted relative risk (SARR) = 1.4, 95% confidence interval (CI) = 1.0, 2.0] with a more marked increase in risk for lung diseases occurring during childhood (SARR = 1.9, 95% CI = 1.2, 3.2) and for tuberculosis (SARR = 10.0, 95% CI = 1.1, 90.1). Family histories of tuberculosis (SARR = 2.0, 95% CI = 1.1, 3.6) and of lung cancer (SARR = 3.9, 95% CI = 2.0, 7.6) were also risk factors for adenocarcinoma of the lung. Increasing risk was observed with decreasing intake of dietary beta-carotene. After adjusting for personal smoking, women in the lowest quartile of intake showed a two-fold increased risk relative to those in the highest quartile of intake (P = 0.003). There were also some suggestive differences between cases and controls in their reproductive history and hormone use.

Effect of interferons and poly(I):poly(C) on the pathogenesis of the diabetogenic variant of encephalomyocarditis virus in different mouse strains

Interferon (IFN) can either prevent or exacerbate the pathogenic effects of the diabetogenic variant of encephalomyocarditis (EMC-D) virus. The effect seen is dependent upon the mouse strain and the time of IFN administration. For example, IFN-alpha beta protects SWR/J but not ICR Swiss male mice against the diabetogenic effects of the virus. Administration of either IFN-alpha beta or the IFN-inducer poly(I):poly(C) 4 days post infection, results in an exacerbation of the infection in ICR Swiss and C57BL/6 male mice. Studies have been initiated to investigate the role of the IFN system in the pathogenesis of this virus infection. In this study IFNs or poly(I):poly(C) were administered to several mouse strains at 24 h before or 4 days after infection with EMC-D virus. The results of such treatment ranged from complete protection of the animals from the diabetogenic effects of the virus to exacerbation of the infection as reflected by the virus content in selected organs. The effect was dependent upon the mouse strain, the type of IFN, and the time of its administration in relation to virus infection.

Prior exposure to medical and dental x-rays related to tumors of the parotid gland

Findings from this population-based study in Los Angeles County suggest, for the first time, that tumors of the parotid gland are related to prior exposure to diagnostic medical and dental radiography. Responses to interviews with 408 patients with a parotid tumor (269 benign tumors and 139 malignant tumors) were compared to responses of 408 neighborhood controls. Cumulative exposure of the parotid gland from diagnostic radiography was associated with a dose-related increase in risk of malignant tumors (P for trend less than .05; relative risk for exposure to greater than or equal to 50 rad = 3.4; 95% confidence interval = 1.02-11.46). Benign tumors showed a weaker positive association, and exposure before age 20 to a major diagnostic examination (full-mouth or panoramic dental radiography or medical radiography to the head) increased risk (relative risk = 1.8; confidence interval = 1.13-2.91). This study also confirmed the association of malignant tumors with prior radiation treatment to the head or neck; 28% of these tumors are attributable to exposure of the parotid gland from diagnostic and therapeutic radiation.

Purification and enzymological characterization of DNA-dependent ATPase IV from the Novikoff hepatoma

DNA-dependent ATPase IV has been purified to near homogeneity from the Novikoff rat hepatoma. The enzyme is devoid of DNA polymerase, RNA polymerase, exonuclease, endonuclease, phosphomonoesterase, 3'- or 5'-phosphodiesterase, polynucleotide kinase, protein kinase, topoisomerase, helicase or DNA reannealing activities at a detection level of 10(-5) to 10(-7) relative to the ATPase activity. The enzyme is a monomer of Mr 110,000, has a sedimentation coefficient of 5.9 S, a Stokes radius of 40 A and a frictional coefficient of 1.32. In the presence of Mg2+ ion and a polynucleotide effector, ATPase IV hydrolyzes either ATP or dATP to the nucleoside diphosphate plus Pi. Other ribo- or deoxyribonucleoside triphosphates are not substrates. ATPase IV utilizes double-stranded DNA and single-stranded DNA as effector; however, it does not utilize poly(dT). The Km for dsDNA or ssDNA is 2.2 microM (nucleotide). A variety of ATP analogues were found to be competitive inhibitors of ATPase IV.