The evaluation of negative epidemiologic studies: the importance of all available evidence in risk characterization

The importance of publishing and utilizing all available epidemiologic evidence in risk assessment is recognized. This recognition includes the findings from negative epidemiologic studies, described as well designed and executed studies where the hypothesized association with an adverse health effect was not found or found to be very weak. In assessing negative evidence, the random (chance) and nonrandom (bias, confounding) sources of variation need to be considered as well as dilution effects, dose-response patterns, biologic plausibility, and methods for data pooling (meta-analysis). Meta-analysis may be a useful statistical approach for a systematic review of results from multiple studies, but cannot overcome the bias of missing evidence.     

RAS mutation is associated with hyperdiploidy and parental characteristics in pediatric acute lymphoblastic leukemia.

We explored the relationship of RAS gene mutations with epidemiologic and cytogenetic factors in a case series of children with leukemia. Diagnostic bone marrow samples from 191 incident leukemia cases from the Northern California Childhood Leukemia Study were typed for NRAS and KRAS codon 12 and 13 mutations. A total of 38 cases (20%) harbored RAS mutations. Among the 142 B-cell acute lymphoblastic leukemia (ALL) cases, RAS mutations were more common among Hispanic children (P=0.11) or children born to mothers <30 years (P=0.007). Those with hyperdiploidy at diagnosis (>50 chromosomes) had the highest rates of RAS mutation (P=0.02). A multivariable model confirmed the significant associations between RAS mutation and both maternal age and hyperdiploidy. Interestingly, smoking of the father in the 3 months prior to pregnancy was reported less frequently among hyperdiploid leukemia patients than among those without hyperdiploidy (P=0.02). The data suggest that RAS and high hyperdiploidy may be cooperative genetic events to produce the leukemia subtype; and furthermore, that maternal age and paternal preconception smoking or other factors associated with these parameters are critical in the etiology of subtypes of childhood leukemia.     

In utero origin of t(8;21) AML1-ETO translocations in childhood acute myeloid leukemia

Recent reports have established the prenatal origin of leukemia translocations and resultant fusion genes in some patients, including MLL-AF4 translocations in infants and TEL-AML1 translocations in children. We now report evidence for the prenatal origin of a translocation in childhood acute myeloid leukemia (AML). The t(8;21) AML1-ETO translocations were sequenced at the genomic level in 10 diagnostic leukemia samples from children with available neonatal Guthrie blood spots. Clonotypic genomic AML1-ETO sequences were detected in the Guthrie spots for 5 individuals, providing unambiguous evidence of prenatal origin in these cases. Two of these patients were older than 10 years of age at diagnosis, indicative of a protracted postnatal latency. Three of the patients were assessed for the persistence of genomic fusion sequences in complete clinical remission samples and were found to be positive. These data indicate that t(8;21) in childhood AML can arise in utero, possibly as an initiating event in childhood AML, and may establish a long-lived or stable parental clone that requires additional secondary genetic alterations to cause leukemia.     

Microaggressions and marijuana use among college students

This study examines the association between exposure to microaggressions and marijuana use, using original survey data from a sample of racial/ethnic minority college students (n?=?332) from a large Division I university in the United States. Nearly all of our sample (96%) reported at least one experience with microaggressions in the past 6 months, while 33% reported using marijuana regularly. We modeled regular use of marijuana using multiple logistic regression, with consideration of sex, age, race/ethnicity, and microaggression scale scores as covariates. Age, sex, the microinvalidations subscale score, and the full microaggression scale score were significantly associated with marijuana use in our full models (p?p?=?.01; p?=?.02; p?=?.03, respectively). With each additional experience of microaggression, the odds of regular marijuana use increase. Academic communities may consider the primary prevention of discriminatory behavior when addressing student substance use.     

Residential traffic density and childhood leukemia risk

BACKGROUND: Exposures to carcinogenic compounds from vehicle exhaust may increase childhood leukemia risk, and the timing of this exposure may be important. METHODS: We examined the association between traffic density and childhood leukemia risk for three time periods: birth, time of diagnosis, and lifetime average, based on complete residential history in a case-control study. Cases were rapidly ascertained from participating hospitals in northern and central California between 1995 and 2002. Controls were selected from birth records, individually matched on age, sex, race, and Hispanic ethnicity. Traffic density was calculated by estimating total vehicle miles traveled per square mile within a 500-foot (152 meter) radius area around each address. We used conditional logistic regression analyses to account for matching factors and to adjust for household income. RESULTS: We included 310 cases of acute lymphocytic leukemias (ALL) and 396 controls in our analysis. The odds ratio for ALL and residential traffic density above the 75th percentile, compared with subjects with zero traffic density, was 1.17 [95% confidence interval (95% CI), 0.76-1.81] for residence at diagnosis and 1.11 (95% CI, 0.70-1.78) for the residence at birth. For average lifetime traffic density, the odds ratio was 1.24 (95% CI, 0.74-2.08) for the highest exposure category. CONCLUSIONS: Living in areas of high traffic density during any of the exposure time periods was not associated with increased risk of childhood ALL in this study.     

Critical windows of exposure to household pesticides and risk of childhood leukemia

The potential etiologic role of household pesticide exposures was examined in the Northern California Childhood Leukemia Study. A total of 162 patients (0-14 years old) with newly diagnosed leukemia were rapidly ascertained during 1995-1999, and 162 matched control subjects were randomly selected from the birth registry. The use of professional pest control services at any time from 1 year before birth to 3 years after was associated with a significantly increased risk of childhood leukemia [odds ratio (OR) = 2.8; 95% confidence interval (CI), 1.4-5.7], and the exposure during year 2 was associated with the highest risk (OR = 3.6; 95% CI, 1.6-8.3). The ORs for exposure to insecticides during the 3 months before pregnancy, pregnancy, and years 1, 2, and 3 were 1.8 (95% CI, 1.1-3.1), 2.1 (95% CI, 1.3-3.5), 1.7 (95% CI, 1.0-2.9), 1.6 (95% CI, 1.0-2.7), and 1.2 (95% CI, 0.7-2.1), respectively. Insecticide exposures early in life appear to be more significant than later exposures, and the highest risk was observed for exposure during pregnancy. Additionally, more frequent exposure to insecticides was associated with a higher risk. In contrast to insecticides, the association between herbicides and leukemia was weak and nonsignificant. Pesticides were also grouped based on where they were applied. Exposure to indoor pesticides was associated with an increased risk, whereas no significant association was observed for exposure to outdoor pesticides. The findings suggest that exposure to household pesticides is associated with an elevated risk of childhood leukemia and further indicate the importance of the timing and location of exposure.     

Use of an index to reflect the aggregate burden of long-term exposure to criteria air pollutants in the United States

Air pollution control in the United States for five common pollutants--particulate matter, ground-level ozone, sulfur dioxide, nitrogen dioxide, and carbon monoxide--is based partly on the attainment of ambient air quality standards that represent a level of air pollution regarded as safe. Regulatory and health agencies often focus on whether standards for short periods are attained; the number of days that standards are exceeded is used to track progress. Efforts to explain air pollution to the public often incorporate an air quality index that represents daily concentrations of pollutants. While effects of short-term exposures have been emphasized, research shows that long-term exposures to lower concentrations of air pollutants can also result in adverse health effects. We developed an aggregate index that represents long-term exposure to these pollutants, using 1995 monitoring data for metropolitan areas obtained from the U.S. Environmental Protection Agency's Aerometric Information Retrieval System. We compared the ranking of metropolitan areas under the proposed aggregate index with the ranking of areas by the number of days that short-term standards were exceeded. The geographic areas with the highest burden of long-term exposures are not, in all cases, the same as those with the most days that exceeded a short-term standard. We believe that an aggregate index of long-term air pollution offers an informative addition to the principal approaches currently used to describe air pollution exposures; further work on an aggregate index representing long-term exposure to air pollutants is warranted.     

Accuracy of multiplexed Illumina platform-based single-nucleotide polymorphism genotyping compared between genomic and whole genome amplified DNA collected from multiple sources.

Association studies designed to identify the genetic determinants underlying complex disease increasingly require sustainable high-quality DNA resources for large-scale single-nucleotide polymorphism (SNP) genotyping. Recent studies have shown that genomic DNA (gDNA) suitable for SNP genotyping can be obtained from buccal cells and from dried blood spots on Guthrie cards. Further, successful SNP genotyping has been done using the reaction product of multiple displacement amplification of gDNA. We evaluated genotype consistency on the Illumina genotyping platform for 717 to 1,744 SNP loci between replicate samples of gDNA and whole genome amplified DNA (wgaDNA) from a variety of sources. Nine healthy adults provided peripheral blood via venipuncture and buccal cells by mouth rinse. DNA was also obtained from urothelial cells in urine samples from five of the nine subjects. gDNA was extracted from all samples, wgaDNA was generated from each gDNA, and all samples were genotyped. To assess SNP genotyping accuracy of DNA obtained from dried blood spots, gDNA was extracted, amplified, and genotyped from peripheral blood samples and paired Guthrie card samples were obtained from eight childhood leukemia patients. Call rates and replicate concordances for all sample types, regardless of amplification, were >97%, with most sample types having call rates and replicate concordances >99%. Using the gDNA from blood samples as the reference for concordances calculated for all other sample types, we observed concordances >98% regardless of sample type or amplification. We conclude that highly multiplexed Illumina genotyping may be done on gDNA and wgaDNA obtained from whole blood, buccal samples, dried blood spots on Guthrie cards, and possibly even urine samples, with minimal misclassification.     

Mesothelioma of childhood

Malignant mesothelioma (MM) of childhood is a rare but important neoplasm. Eighty children with a previous diagnosis of MM were identified. Four of the 80 children had exposure to known risk factors (two had history of exposure to asbestos, one had received radiation therapy, and one had been exposed in utero to isoniazid). Tissue slides were available for independent and joint review by a panel of three pathologists in 22 of the cases. Ten were accepted as MM, nine were reclassified as other malignancies, and three were considered tumors of uncertain nature. Six of the ten children with MM were boys, and four were girls. Eight had pleural tumors, and two had peritoneal tumors. Four died at 7, 8, 18, and 48 months after diagnosis; three remained alive at 19, 20, and 59 months; and three had no follow-up. This review suggests that MM of childhood is a valid entity with a grave prognosis. The tissue diagnosis is difficult and is best made by a panel of pathologists. The available evidence does not support a causal relationship between MM and asbestos, radiation, or isoniazid.