Ascertainment bias in rate ratio estimation from case-sibling control studies of variable age-at-onset diseases.

Motivated by a Finnish case-control study of early onset diabetes in which diabetic children are matched to sibling controls, we investigate ascertainment bias of the usual rate ratio estimator from case-control data under simplex complete ascertainment of families during a fixed interval of time. Analytic results indicate that the assumptions necessary for valid estimation are that the disease is rare and the factors under study are exchangeable--essentially that the covariate distribution does not depend on calendar time or birth order. Further, we found that the rare disease assumption could be dropped by restricting to cases that were diagnosed during the enrollment period of the study or including all cases but eliminating the proband as a control for non-enrollment-period cases. An important consequence of this work is that standard family-based case-control studies are subject to ascertainment bias if exchangeability of the covariates under investigation does not hold.

Predictive value of prior Rose angina for myocardial infarction confirmation after emergency admissions.

The Rose Questionnaire, developed to facilitate screening for the presence of coronary artery disease, has shown good utility for white men and more variable utility among Latino, African-American, and female subjects. This study investigated its utility for prediction of outcome in patients with suspected myocardial infarction. A total of 1428 white, Latino, and African-American subjects completed questionnaires after emergency admission, which were correlated with diagnoses at the time of discharge from a public hospital and private hospital. Results indicated that subjects with positive questionnaires were less likely to have infarction confirmed at discharge, except for those with a prior history of myocardial infarction, than those with a negative response. These data are important in evaluating the overall utility of the Rose Questionnaire and the significance of angina.

Detection of gene-environment interactions in joint segregation and linkage analysis.

We compare approaches for analysis of gene-environment (G x E) interaction, using segregation and joint segregation and linkage analyses of a quantitative trait. Analyses of triglyceride levels in a single large pedigree demonstrate the two methods and show evidence for a significant interaction (P=.015 when segregation analysis is used; P=.006 when joint analysis is used) between a codominant major gene and body-mass index. Genotype-specific correlation coefficients, between triglyceride levels and body-mass index, estimated from the joint model are rAA=.72, rAa=.49, and raa=. 20. Several simulation studies indicate that joint segregation and linkage analysis leads to less-biased and more-efficient estimates of a G x E-interaction effect, compared with segregation analysis alone. Depending on the heterozygosity of the marker locus and its proximity to the trait locus, we found joint analysis to be as much as 70% more efficient than segregation analysis, for estimation of a G x E-interaction effect. Over a variety of parameter combinations, joint analysis also led to moderate (5%-10%) increases in power to detect the interaction. On the basis of these results, we suggest the use of combined segregation and linkage analysis for improved estimation of G x E-interaction effects when the underlying trait gene is unmeasured.

Joint segregation and linkage analysis of a quantitative trait compared to separate analyses.

Our goal was to determine the degree to which joint segregation and linkage analysis leads to increased efficiency for estimating the recombination fraction and to greater power for detecting linkage, compared to separate analyses. We concentrated on the quantitative phenotype Q2 and analyzed linkage with a tightly linked marker, a loosely linked marker, and eight unlinked markers, the latter chosen to evaluate false positive rates. We considered both nuclear-family and extended-pedigree data, using the 200 replicates of each provided to GAW participants. We found joint analysis to be consistently more efficient, with relative efficiencies for the tightly linked marker of 1.16 and 1.06 in extended pedigrees and nuclear families, respectively. These relative efficiencies translated into modest but consistent gains in power to detect linkage. Both methods appear to produce unbiased parameter estimates and similar false positive rates.

Simultaneously modelling censored survival data and repeatedly measured covariates: a Gibbs sampling approach.

Recent methodologic developments in the analysis of longitudinal data have typically addressed one of two aspects: (i) the modelling of repeated measurements of a covariate as a function of time or other covariates, or (ii) the modelling of the effect of a covariate on disease risk. In this paper, we address both of these issues in a single analysis by modelling a continuous covariate over time and simultaneously relating the covariate to disease risk. We use the Markov chain Monte Carlo technique of Gibbs sampling to estimate the joint posterior distribution of the unknown parameters of the model. Simulation studies showed that jointly modelling survival and covariate data reduced bias in parameter estimates due to covariate measurement error and informative censoring. We illustrate the methodology by application to a data set that consists of repeated measurements of the immunologic marker CD4 and times of diagnosis of AIDS for a cohort of anti-HIV-1 positive recipients of anti-HIV-1 positive blood transfusions. We assume a linear random effects model with subject-specific intercepts and slopes and normal errors for the true log and square root CD4 counts, and a proportional hazards model for AIDS-free survival time expressed as a function of current true CD4 value. On the square root scale, the joint approach yielded a mean slope for CD4 that was 7 per cent steeper and a log relative risk of AIDS that was 35 per cent larger than those obtained by analysis of the component sub-models separately.

Monitoring dietary change in a low-fat diet intervention study: advantages of using 24-hour dietary recalls vs food records.

OBJECTIVE: The purpose of the study was to evaluate two methods of dietary assessment for monitoring change in fat intake in a low-fat diet intervention study. DESIGN: The two dietary assessment methods were a 4-day food record (4DFR) and an unannounced 24-hour dietary recall conducted by telephone interview (referred to as a telephone recall [TR]). Subjects were assigned randomly to either a low-fat diet intervention group or a control group that received no counseling about fat intake. Dietary data were collected at baseline, 6 months, and 12 months. SUBJECTS: Two hundred ninety postmenopausal women with localized breast cancer were recruited at seven clinical centers in the United States. STATISTICAL ANALYSIS: Analysis of variance was used to test for significant differences in mean fat and energy intakes. RESULTS: Three sources of error were identified: (a) an instrument effect, suggesting underreporting at baseline of approximately 8% in mean energy intake and 11% in mean fat intake in the TR group compared with the 4DFR group (P = .0001); (b) a repeated measures effect observed for the 4DFR, suggesting underreporting of approximately 7% for energy intake and 14% for fat intake in the control group at 6 and 12 months compared with baseline values (P < .001); and (c) an adherence effect (or compliance bias), suggesting greater compliance to the low-fat intervention diet when subjects were keeping food records than when estimates were based on the unannounced TR. Compared with the TR, the 4DFR overestimated the extent of fat reduction in the low-fat diet intervention group by 41% (P = .08) and 25% (P = .62) at 6 and 12 months, respectively. APPLICATION: Multiple days of unannounced 24-hour recalls may be preferable to multiple-day food records for monitoring dietary change in diet intervention studies.

Genetic epidemiologic analysis of quantitative phenotypes using Gibbs sampling.

We analyzed two quantitative traits (Q1 and Q2) provided in the 'Common Disease' data set with the aim of detecting both genetic and environmental determinants. We used linear regression for screening measured variables, maximum likelihood segregation and linkage analyses for detecting and localizing unmeasured genes, and Gibbs sampling for joint segregation and linkage analyses with estimation of gene-environment interaction and polygenic effects. For both Q1 and Q2, we successfully detected the unmeasured codominant major gene (MG) that was tightly linked to candidate gene C2. We also detected all of the measured variables used in generating Q1 (age, Q3, candidate gene C5) and Q2 (EF). Although our final models differed slightly from the true data generation models, our multifaceted analytic approach was successful in characterizing the determinants of Q1 and Q2.

Prediction of systemic fungal infection in allogeneic marrow recipients: impact of amphotericin prophylaxis in high-risk patients.

PURPOSE: To identify risk factors that might predict for systemic fungal infections in marrow transplant recipients within the first 100 days and to assess the efficacy of low-dose amphotericin B used as prophylaxis for candidemia and infection with invasive Aspergillus species in patients at risk. PATIENTS AND METHODS: A retrospective analysis of transplant outcomes for 331 allogeneic marrow recipients transplanted between 1983 and 1989 was performed to identify patients who might be at increased risk of fungal infection. Factors analyzed included disease, remission status, transplant regimen, graft-versus-host disease (GVHD) prophylaxis, duration of neutropenia, and development of GVHD. A trial of low-dose amphotericin (5 to 10 mg/d) begun on day +1 and continuing for 2 to 3 months posttransplant was begun in 1987 to evaluate its utility in reducing systemic mycoses. RESULTS: There were 18 episodes of candidemia and 18 systemic mycoses documented by blood or tissue culture or by biopsy. The initiation of high-dose (0.5 to 1 mg/kg/d) corticosteroids early as a component of GVHD prophylaxis in 1986 was identified as the most important risk factor for fungal infections, with a sixfold increase in infections as compared with the previous GVHD regimen (P < .0001); this was despite a significant decrease in the incidence of grade II to IV GVHD (7% v 43%; P = .0001). Low-dose amphotericin B initiated before the start of high-dose corticosteroid GVHD prophylaxis reduced the incidence of fungal infections from 30% to 9% (P = .01) without renal toxicity. Cyclosporine levels were lower in the patients who received amphotericin, leading to an increase in the rate of GVHD to 19% (P = .02). Controlling for GVHD prophylaxis, prolonged neutropenia (P = .00), and grade II to IV GVHD (P = .01) were also identified as risk factors for fungal infection. CONCLUSION: Amphotericin B can be used in low doses as prophylaxis for fungal infections early in the posttransplant course. However, cyclosporine doses need to be monitored to maintain target levels.

Combined segregation and linkage analysis of late-onset Alzheimer's disease in Duke families using Gibbs sampling.

We illustrate the use of Gibbs sampling for combined segregation and linkage analysis using late-onset families in the Duke Alzheimer's disease (AD) data set. The disease penetrance model is flexible, incorporating variable age of disease onset, sporadic cases, and unknown or uncertain ages of AD onset. Model parameters (including allele frequencies) and lod scores are estimated, and a correction for ascertainment is made. Little indication of linkage was observed for any chromosome 19 or 21 marker. However, there was strong evidence for the existence of an AD major gene under an autosomal dominant/sporadic model.

Immunohistochemical assay of neu/c-erbB-2 oncogene product in paraffin-embedded tissues in early breast cancer: retrospective follow-up study of 245 stage I and II cases.

The expression of neu oncoprotein was assayed by immunohistochemistry (IHC) on 245 paraffin-embedded, Stage I and II breast cancers from patients treated at the City of Hope between the years 1980 and 1987. Only cases showing membrane staining were scored as positive. Fifty-four (22%) of the tumors stained positively for neu. Probability of disease-free survival (DFS) and overall survival (OS) was compared based on neu positivity and other prognostic factors. Overall, DFS and OS did not differ significantly among neu-positive and neu-negative cases. However, when only cases with favorable (Stages I and II) nuclear grade were analyzed, OS and DFS were significantly lower in neu-positive cases, with a 9-fold increase in risk of death and a 3-fold increase in risk of relapse. Our findings suggest that immunohistologic study of neu oncoprotein may help to define patients at greater risk among low-stage/low-nuclear-grade patients with breast cancer, a group hitherto recognized as having a good prognosis.

Ocular acyclovir delivery by collagen discs: a mouse model to screen anti-viral agents.

Discs 1.6 mm in diameter trephined from corneal collagen shields were used to deliver acyclovir (ACV) to the cornea of mice inoculated with herpes simplex virus type 1 (HSV-1). In the first minute after application to the cornea, there was a 23% decrease of ACV in the discs. After the first minute, ACV clearance from the discs appeared to be exponential with a half-life of 21 minutes. Treatment given 3 times a day reduced HSV-1 titer in tear film, corneal tissue, and trigeminal ganglia. This animal model should be useful to conserve novel potential anti-viral drugs undergoing initial screening.

Infection with human immunodeficiency virus type 1 (HIV-1) among recipients of antibody-positive blood donations.

OBJECTIVE: To assess the incidence of human immunodeficiency virus type 1(HIV-1) transmission by antibody (anti-HIV-1)-positive blood components, and to determine the immunologic and clinical course in HIV-1-infected recipients. DESIGN AND SUBJECTS: We retrospectively tested approximately 200,000 donor blood component specimens stored in late 1984 and 1985 for anti-HIV-1, and we contacted recipients of positive specimens to determine their serologic status. They were compared with both recipients of HIV-1-negative transfusions and healthy (untransfused) controls. Subjects were seen at 3- to 6-month intervals for up to 4 years for clinical and immunologic evaluations. MEASUREMENTS AND MAIN RESULTS: Of 133 recipients, 9 had other possible exposures. Excluding these cases, 111 of 124 (89.5%) were anti-HIV-1-positive (95% CI, 84.1% to 94.5%). The recipient's sex, age, underlying condition, and type of component did not influence infection rates. The cumulative risk for developing the acquired immunodeficiency syndrome (AIDS) within 38 months after transfusion was 13% (CI, 7.5% to 21.6%). At 36 +/- 3 months after the index transfusion, seropositive recipients had lower counts of CD2+CDw26+, CD4+, CD4+CD29+, and CD4+CD45RA+subsets and more CD8+I2+ lymphocytes than did recipients of anti-HIV-1-negative transfusions. The CD4+ and CD2+CDw26+subsets changed the most rapidly. The absolute CD8+ count remained normal. CONCLUSIONS: Transfusion of anti-HIV-1-positive blood infected 90% of recipients. The rate of progression to AIDS within the first 38 months after infection was similar to that reported for homosexual men and hemophiliacs. Although most lymphocyte subset counts changed over time, CD8+ counts were constant.