Karen K. Steinberg

DNA banking for epidemiologic studies: a review of current practices.

To study genetic risk factors for common diseases, researchers have begun collecting DNA specimens in large epidemiologic studies and surveys. However, little information is available to guide researchers in selecting the most appropriate specimens. In an effort to gather the best information for the selection of specimens for these studies, we convened a meeting of scientists engaged in DNA banking for large epidemiologic studies. In this discussion, we review the information presented at that meeting in the context of recent published information. Factors to be considered in choosing the appropriate specimens for epidemiologic studies include quality and quantity of DNA, convenience of collection and storage, cost, and ability to accommodate future needs for genotyping. We focus on four types of specimens that are stored in these banks: (1) whole blood preserved as dried blood spots; (2) whole blood from which genomic DNA is isolated, (3) immortalized lymphocytes from whole blood or separated lymphocytes, prepared immediately or subsequent to cryopreservation; and (4) buccal epithelial cells. Each of the specimens discussed is useful for epidemiologic studies according to specific needs, which we enumerate in our conclusions.

Breast cancer risk and duration of estrogen use: the role of study design in meta-analysis.

Recent meta-analyses of studies of the risk of breast cancer associated with hormone replacement therapy agree that little risk is associated with ever-use or short-term use of estrogen replacement. These analyses disagree, however, about the effect of long-duration estrogen use. To understand differences in the findings among the meta-analyses of the effect of long-term use, we investigated the source of heterogeneity among the included studies. We analyzed subgroups by source of controls (community vs hospital), study design (case-control vs follow-up), and types of estrogen. We also examined the effect of modeling assumptions: that before women began estrogen use, those who chose to use estrogen replacement (1) were, or (2) were not, at substantially different risk from those who chose not to use estrogen. We found a small increase in risk in all subgroups of studies except those that used hospital controls. From a homogeneous group of case-control studies using community controls that analyzed the effect of conjugated equine estrogens, we estimated that the risk of breast cancer after 10 years of estrogen use increased by at least 15% and up to 29%.

Effect of Low-level Body Burdens of Lead on the Mental Development of Children: Limitations of Meta-analysis in a Review of Longitudinal Data

The effect of low-level body burdens of lead on the intelligence of children, as measured by intelligence quotient (IQ), was assessed. We reviewed 35 reports from five longitudinal studies conducted in the United States and Australia. In each of these studies, infants were followed for 58 mo or less. The study populations consisted of low- and middle-socioeconomic-class infants who had low-level exposure to environmental lead. Blood-lead levels were measured in a standard fashion at various times, beginning in the prenatal period, and intelligence was first measured at 6 mo of age and was followed by subsequent assessments. Studies were assessed for quality by a review panel blinded to the identity of the investigators and their affiliations. Efforts were made to pool the data with meta-analytic techniques, but efforts were unsuccessful because the methods used to analyze and report data were inconsistent. Inconsistencies were as follows: (a) there were few instances in which IQ and blood-lead levels were measured at comparable times in different studies; (b) incompatibilities existed among the studies, including differences in independent variables, data transformations, and statistical parameters reported; (c) results conflicted when measurement intervals were comparable (i.e., heterogeneity); (d) patterns of regression and correlation coefficients were inconsistent; and (e) data were insufficient to interconvert the parameters reported. Consequently, definitive conclusions regarding the effect of low-level body burdens of lead on IQ could not be determined from the longitudinal data. Examination of the weight of the evidence from this and other studies, however, suggests an adverse relationship of lead on the intelligence of children.

BRCA1 and BRCA2 gene mutations and risk of breast cancer:: Public health perspectives

CONTENT Breast cancer is the most common cancer and the second most common cause of cancer death among U.S. women. In 1998, about 178,700 new cases will be diagnosed and 43,500 women will die from the disease. Mutations in the BRCA1 gene, which was cloned in 1994 and is located on chromosome 17q, have been identified as causes of predisposition to breast, ovarian, and other cancers. A second breast cancer gene, BRCA2, has been localized to chromosome 13q. Using inferential procedures, the overall carrier frequency of BRCA1 gene mutations has been estimated at 1 in 500 in the general U.S. population. Recent studies have indicated that the carrier frequency of a specific BRCA1 allele, the 185delAG mutation, may be as high as 0.8% to 1% among women of Ashkenazi Jewish descent. CONCLUSIONS Due to the proliferation of laboratories offering genetic tests for breast cancer susceptibility, their appropriate use in public health needs careful scrutiny. Several issues are raised when such genetic tests are considered for population-based prevention programs for breast cancer. Public health agencies, such as the Centers for Disease Control and Prevention, are important to monitoring and evaluating genetic testing done outside of research protocols. If genetic tests for breast cancer are to be incorporated into future prevention programs, evaluation is needed of whether the testing can have the intended effect.

Genetic Studies of a Cluster of Acute Lymphoblastic Leukemia Cases in Churchill County, Nevada

Objective In a study to identify exposures associated with 15 cases of childhood leukemia, we found levels of tungsten, arsenic, and dichlorodiphenyldichloroethylene in participants to be higher than mean values reported in the National Report on Human Exposure to Environmental Chemicals. Because case and comparison families had similar levels of these contaminants, we conducted genetic studies to identify gene polymorphisms that might have made case children more susceptible than comparison children to effects of the exposures. Design We compared case with comparison children to determine whether differences existed in the frequency of polymorphic genes, including genes that code for enzymes in the folate and purine pathways. We also included discovery of polymorphic forms of genes that code for enzymes that are inhibited by tungsten: xanthine dehydrogenase, sulfite oxidase (SUOX gene), and aldehyde oxidase. Participants Eleven case children were age- and sex-matched with 42 community comparison children for genetic analyses. Twenty parents of case children also contributed to the analyses. Results One bilalleleic gene locus in SUOX was significantly associated with either case or comparison status, depending on which alleles the child carried (without adjusting for multiple comparisons). Conclusions Although genetic studies did not provide evidence that a common agent or genetic susceptibility factor caused the leukemias, the association between a SUOX gene locus and disease status in the presence of high tungsten and arsenic levels warrants further investigation. Relevance Although analyses of community clusters of cancer have rarely identified causes, these findings have generated hypotheses to be tested in subsequent studies.

HFE genotype and transferrin saturation in the United States.

Purpose: Examine the penetrance (defined by high transferrin saturation [TS]) of C282Y and H63D in the U.S. population.Methods: 5171 participants from the Third National Health and Nutrition Examination Survey, 1992 to 1994.Results: 77.1% (95% confidence interval [CI], 2.3, 95.1) of men and 51.9% (95% CI, 0, 84.2) of women with C282Y homozygosity had high TS. The associations of H63D homozygosity with high TS were stronger in people aged 50 years or older than in younger persons. Among Mexican-Americans, simple H63D heterozygosity was associated with high TS.Conclusions: The associations between HFE genotype and high TS may vary by sex, age, and ethnic group.

Thrombomodulin Ala455Val Polymorphism and the risk of cerebral infarction in a biracial population: the Stroke Prevention in Young Women Study

BackgroundThe genes encoding proteins in the thrombomodulin-protein C pathway are promising candidate genes for stroke susceptibility because of their importance in thrombosis regulation and inflammatory response. Several published studies have shown that the Ala455Val thrombomodulin polymorphism is associated with ischemic heart disease, but none has examined the association with stroke. Using data from the Stroke Prevention in Young Women Study, we sought to determine the association between the Ala455Val thrombomodulin polymorphism and the occurrence of ischemic stroke in young women.MethodsAll 59 hospitals in the greater Baltimore-Washington area participated in a population-based case-control study of stroke in young women. We compared 141 cases of first ischemic stroke (44% black) among women 15 to 44 years of age with 210 control subjects (35% black) who were identified by random digit dialing and frequency matched to the cases by age and geographical region of residence. Data on historical risk factors were collected by standardized interview. Genotyping of the thrombomodulin Ala455Val polymorphism was performed by pyrosequencing.ResultsThe A allele (frequency = 0.85) was associated with stroke under the recessive model. After adjustment for age, race, cigarette smoking, hypertension, and diabetes, the AA genotype, compared with the AV and VV genotypes combined, was significantly associated with stroke (odds ratio 1.9, 95% CI 1.1–3.3). The AA genotype was more common among black than white control subjects (81% versus 68%) but there was no significant interaction between the risk genotype and race (adjusted odds ratio 2.7 for blacks and 1.6 for whites). A secondary analysis removing all probable (n = 16) and possible (n = 15) cardioembolic strokes demonstrated an increased association (odds ratio 2.2, 95% CI 1.2–4.2).ConclusionsAmong women aged 15 to 44 years, the AA genotype is more prevalent among blacks than whites and is associated with increased risk of early onset ischemic stroke. Removing strokes potentially related to cardioembolic phenomena increased this association. Further studies are needed to determine whether this polymorphism is functionally related to thrombomodulin expression or whether the association is due to population stratification or linkage to a nearby functional polymorphism.

The Ethics of Access to Online Genetic Databases

With the sequencing of the human genome comes the promise of advances in medical science. For this promise to be fully realized, researchers must have access to information resulting from this landmark endeavor as well as from subsequent research initiatives. However, because genomic sequences are potential sources of profit for the biotechnology and pharmaceutical industries, many private companies seek to limit access to this information. Some argue that this will impede scientific progress and increase the cost of basic research, while others argue that the privatization of genetic information is needed to assure profits and generate the considerable funding necessary to bring therapeutic products to the market. In analyzing the arguments for both sides, we conclude that both private funding and public access to information are important in genetic research. Precedents for compromise are necessary, as is increased dialog between private and public interests in order to ensure continued advancements in genetic science and medicine.

Predicting Type 1 Diabetes Using Autoantibodies: The Latest Results from the Diabetes Autoantibody Standardization Program

397 THE BEST CURRENT MEANS of identifying those at high risk for type 1 diabetes before the development of clinical symptoms is through the measurement of autoantibodies to islet cell antigens.1–6 These tests are widely used to identify candidates at increased risk for developing type 1 diabetes for intervention trials7,8 and patients requiring insulin treatment,9 to help classify diabetes,10 and to study the natural history of diabetes.11–13 Islet autoantibody assays are currently performed by certain centers of expertise throughout the world, and the Immunology of Diabetes Society (IDS) has shown in its previous workshops that the performance of the assays at different sites varies considerably.14–16 Better agreement of these methods is essential for the comparison of the results of different intervention trials and natural history studies, and for the recruitment of patients in multicenter trials. In 1999 the Centers for Disease Control and Prevention’s (CDC’s) National Diabetes Laboratory joined with the IDS to form the Diabetes Autoantibody Standardization Program (DASP) to improve the performance of these assays and provide an accuracy base for the development of new assay technologies. The major goals of DASP are to help laboratories to improve their methods, provide technical support, provide training and information on the best methods, support the development of highly sensitive and specific measurement technologies, and develop reference materials as an accuracy base. CDC reference methods are also being developed on the basis of the best available technology. In addition to the first immunohistochemical islet cell antibody assay, which utilizes pancreatic tissue and proved difficult to standardize, there are three major autoantibody antigens in common use in biochemical assays that require only small amounts of sera: glutamic acid decarboxylase (GAD), protein tyrosine phosphatase (IA-2), and insulin. Methods commonly used to produce antigen for these assays include in vitro transcription and translation of the coding DNA with incorporation of radioisotope-labeled amino acids, or labeling the proteins directly by iodination using 125I. The autoantibodies bound to the antigens are then commonly measured using radiobinding assays. These methods are complex and are quite sensitive to differences in technique.

Increased risk for familial ovarian cancer among Jewish women : A population-based case-control study

Jewish women have been reported to have a higher risk for familial breast cancer than non‐Jewish women and to be more likely to carry mutations in breast cancer genes such as BRCA1. Because BRCA1 mutations also increase womens risk for ovarian cancer, we asked whether Jewish women are at higher risk for familial ovarian cancer than non‐Jewish women. To determine the effects of 1) Jewish religion and 2) ovarian cancer in a first‐degree relative on womens risk for epithelial ovarian cancer, we used data from a population‐based, case‐control study conducted in 8 geographic regions in the United States from 1980 through 1982. The study group included 471 cases and 4,025 controls. Jewish women were more likely to have familial ovarian cancer than non‐Jewish women [odds ratio (OR) = 8.4,95% confidence interval (CI) = 2.6–28]. The risk of having ovarian cancer appeared to be greater in Jewish women having a first‐degree relative with ovarian cancer (OR = 8.81,95% CI = 2.02–38.23) than in non‐Jewish women having a first‐degree relative with ovarian cancer (OR = 3.01,95% CI = 1.61–5.64), but differences between Jewish and non‐Jewish women were not statistically significant. Jewish women with no first‐degree relative with ovarian cancer had no increased risk for ovarian cancer (OR = 1.27,95% CI = 0.74–2.91) compared to non‐Jewish women. These results suggest that Jewish women may have a higher rate of familial ovarian cancer than non‐Jewish women, but because the results are based on a small number of Jewish women with familial ovarian cancer, the results need to be confirmed in larger studies. Genet. Epidemiol. 15:51–59,1998.