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Search Results: 1 - 10 of 325418 matches for " Krista S. Crider "
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Defying birth defects through diet?
Krista S Crider, Lynn B Bailey
Genome Medicine , 2011, DOI: 10.1186/gm223
Abstract: The initial formation of many major structures of the human embryo takes place during a very narrow window of time in the first weeks after conception, often before a woman even knows she is pregnant. Any change in the early embryonic environment, including nutrient availability, has the potential to adversely or positively affect the developing embryo. Evidence is evolving that specific components of maternal diet can play a critical role in modifying the risk for birth defects.The best example of the influence of maternal diet on birth defect risk is the intake of folic acid for prevention of neural tube defects (NTDs) [1]. Randomized controlled folic acid intervention trials demonstrating the effectiveness of folic acid for NTD risk reduction have led to the current public health recommendation, as well as folic acid fortification of the food supply [1]. Prevention of NTDs with supplemental folic acid is likely to involve a complex interaction between folic acid and multiple genetic factors; this is the focus of ongoing investigations [1].The success of folic acid supplementation in reducing NTDs has led researchers to evaluate the association of other dietary components, such as fat, with a risk for birth defects. Researchers have found that pre-pregnancy diabetes and obesity are associated with an increased risk for numerous birth defects (for example, specific heart defects, NTDs and cleft palate) [2]. A recent meta-analysis revealed that certain aspects of preconception care reduced the risk for some birth defects among women with diabetes: the risk reductions were associated with changes in behavior, such as increased folic acid use or improved glycemic control, or both (depending on the study) [2]. Both diabetes and obesity are related etiologically to high-fat diets, although the mechanisms by which these conditions are or might be teratogenic during pregnancy are unclear. A high-fat western diet has been shown in a retrospective case-control study to be a
Folic Acid Food Fortification—Its History, Effect, Concerns, and Future Directions
Krista S. Crider,Lynn B. Bailey,Robert J. Berry
Nutrients , 2011, DOI: 10.3390/nu3030370
Abstract: Periconceptional intake of folic acid is known to reduce a woman’s risk of having an infant affected by a neural tube birth defect (NTD). National programs to mandate fortification of food with folic acid have reduced the prevalence of NTDs worldwide. Uncertainty surrounding possible unintended consequences has led to concerns about higher folic acid intake and food fortification programs. This uncertainty emphasizes the need to continually monitor fortification programs for accurate measures of their effect and the ability to address concerns as they arise. This review highlights the history, effect, concerns, and future directions of folic acid food fortification programs.
Hypomethylation of Serum Blood Clot DNA, but Not Plasma EDTA-Blood Cell Pellet DNA, from Vitamin B12-Deficient Subjects
Eoin P. Quinlivan, Krista S. Crider, Jiang-Hui Zhu, David R. Maneval, Ling Hao, Zhu Li, Sonja A. Rasmussen, R. J. Berry, Lynn B. Bailey
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0065241
Abstract: Vitamin B12, a co-factor in methyl-group transfer, is important in maintaining DNA (deoxycytidine) methylation. Using two independent assays we examined the effect of vitamin B12-deficiency (plasma vitamin B12<148 pmol/L) on DNA methylation in women of childbearing age. Coagulated blood clot DNA from vitamin B12-deficient women had significantly (p<0.001) lower percentage deoxycytidine methylation (3.23±0.66%; n = 248) and greater [3 H]methyl-acceptance (42,859±9,699 cpm; n = 17) than DNA from B12-replete women (4.44±0.18%; n = 128 and 26,049±2,814 cpm; n = 11) [correlation between assays: r = –0.8538; p<0.001; n = 28]. In contrast, uncoagulated EDTA-blood cell pellet DNA from vitamin B12-deficient and B12-replete women exhibited similar percentage methylation (4.45±0.15%; n = 77 vs. 4.47±0.15%; n = 47) and [3 H]methyl-acceptance (27,378±4,094 cpm; n = 17 vs. 26,610±2,292 cpm; n = 11). Therefore, in simultaneously collected paired blood samples, vitamin B12-deficiency was associated with decreased DNA methylation only in coagulated samples. These findings highlight the importance of sample collection methods in epigenetic studies, and the potential impact biological processes can have on DNA methylation during collection.
Genomic DNA Methylation Changes in Response to Folic Acid Supplementation in a Population-Based Intervention Study among Women of Reproductive Age
Krista S. Crider, Eoin P. Quinlivan, Robert J. Berry, Ling Hao, Zhu Li, David Maneval, Thomas P. Yang, Sonja A. Rasmussen, Quanhe Yang, Jiang-Hui Zhu, Dale J. Hu, Lynn B. Bailey
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0028144
Abstract: Folate is a source of one-carbons necessary for DNA methylation, a critical epigenetic modification necessary for genomic structure and function. The use of supplemental folic acid is widespread however; the potential influence on DNA methylation is unclear. We measured global DNA methylation using DNA extracted from samples from a population-based, double-blind randomized trial of folic acid supplementation (100, 400, 4000 μg per day) taken for 6 months; including a 3 month post-supplementation sample. We observed no changes in global DNA methylation in response to up to 4,000 μg/day for 6 months supplementation in DNA extracted from uncoagulated blood (approximates circulating blood). However, when DNA methylation was determined in coagulated samples from the same individuals at the same time, significant time, dose, and MTHFR genotype-dependent changes were observed. The baseline level of DNA methylation was the same for uncoagulated and coagulated samples; marked differences between sample types were observed only after intervention. In DNA from coagulated blood, DNA methylation decreased (?14%; P<0.001) after 1 month of supplementation and 3 months after supplement withdrawal, methylation decreased an additional 23% (P<0.001) with significant variation among individuals (max+17%; min-94%). Decreases in methylation of ≥25% (vs. <25%) after discontinuation of supplementation were strongly associated with genotype: MTHFR CC vs. TT (adjusted odds ratio [aOR] 12.9, 95%CI 6.4, 26.0). The unexpected difference in DNA methylation between DNA extracted from coagulated and uncoagulated samples in response to folic acid supplementation is an important finding for evaluating use of folic acid and investigating the potential effects of folic acid supplementation on coagulation.
Invasive Fishes Generate Biogeochemical Hotspots in a Nutrient-Limited System
Krista A. Capps, Alexander S. Flecker
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0054093
Abstract: Fishes can play important functional roles in the nutrient dynamics of freshwater systems. Aggregating fishes have the potential to generate areas of increased biogeochemical activity, or hotspots, in streams and rivers. Many of the studies documenting the functional role of fishes in nutrient dynamics have focused on native fish species; however, introduced fishes may restructure nutrient storage and cycling freshwater systems as they can attain high population densities in novel environments. The purpose of this study was to examine the impact of a non-native catfish (Loricariidae: Pterygoplichthys) on nitrogen and phosphorus remineralization and estimate whether large aggregations of these fish generate measurable biogeochemical hotspots within nutrient-limited ecosystems. Loricariids formed large aggregations during daylight hours and dispersed throughout the stream during evening hours to graze benthic habitats. Excretion rates of phosphorus were twice as great during nighttime hours when fishes were actively feeding; however, there was no diel pattern in nitrogen excretion rates. Our results indicate that spatially heterogeneous aggregations of loricariids can significantly elevate dissolved nutrient concentrations via excretion relative to ambient nitrogen and phosphorus concentrations during daylight hours, creating biogeochemical hotspots and potentially altering nutrient dynamics in invaded systems.
Respondent-Driven Sampling: An Assessment of Current Methodology
Krista J. Gile,Mark S. Handcock
Statistics , 2009,
Abstract: Respondent-Driven Sampling (RDS) employs a variant of a link-tracing network sampling strategy to collect data from hard-to-reach populations. By tracing the links in the underlying social network, the process exploits the social structure to expand the sample and reduce its dependence on the initial (convenience) sample. The primary goal of RDS is typically to estimate population averages in the hard-to-reach population. The current estimates make strong assumptions in order to treat the data as a probability sample. In particular, we evaluate three critical sensitivities of the estimators: to bias induced by the initial sample, to uncontrollable features of respondent behavior, and to the without-replacement structure of sampling. This paper sounds a cautionary note for the users of RDS. While current RDS methodology is powerful and clever, the favorable statistical properties claimed for the current estimates are shown to be heavily dependent on often unrealistic assumptions.
On the Concept of Snowball Sampling
Mark S. Handcock,Krista J. Gile
Statistics , 2011,
Abstract: This brief comment reflects on the historical and current uses of the term "snowball sampling."
Network Model-Assisted Inference from Respondent-Driven Sampling Data
Krista J. Gile,Mark S. Handcock
Statistics , 2011,
Abstract: Respondent-Driven Sampling is a method to sample hard-to-reach human populations by link-tracing over their social networks. Beginning with a convenience sample, each person sampled is given a small number of uniquely identified coupons to distribute to other members of the target population, making them eligible for enrollment in the study. This can be an effective means to collect large diverse samples from many populations. Inference from such data requires specialized techniques for two reasons. Unlike in standard sampling designs, the sampling process is both partially beyond the control of the researcher, and partially implicitly defined. Therefore, it is not generally possible to directly compute the sampling weights necessary for traditional design-based inference. Any likelihood-based inference requires the modeling of the complex sampling process often beginning with a convenience sample. We introduce a model-assisted approach, resulting in a design-based estimator leveraging a working model for the structure of the population over which sampling is conducted. We demonstrate that the new estimator has improved performance compared to existing estimators and is able to adjust for the bias induced by the selection of the initial sample. We present sensitivity analyses for unknown population sizes and the misspecification of the working network model. We develop a bootstrap procedure to compute measures of uncertainty. We apply the method to the estimation of HIV prevalence in a population of injecting drug users (IDU) in the Ukraine, and show how it can be extended to include application-specific information.
Modeling social networks from sampled data
Mark S. Handcock,Krista J. Gile
Statistics , 2010, DOI: 10.1214/08-AOAS221
Abstract: Network models are widely used to represent relational information among interacting units and the structural implications of these relations. Recently, social network studies have focused a great deal of attention on random graph models of networks whose nodes represent individual social actors and whose edges represent a specified relationship between the actors. Most inference for social network models assumes that the presence or absence of all possible links is observed, that the information is completely reliable, and that there are no measurement (e.g., recording) errors. This is clearly not true in practice, as much network data is collected though sample surveys. In addition even if a census of a population is attempted, individuals and links between individuals are missed (i.e., do not appear in the recorded data). In this paper we develop the conceptual and computational theory for inference based on sampled network information. We first review forms of network sampling designs used in practice. We consider inference from the likelihood framework, and develop a typology of network data that reflects their treatment within this frame. We then develop inference for social network models based on information from adaptive network designs. We motivate and illustrate these ideas by analyzing the effect of link-tracing sampling designs on a collaboration network.
Aggression and Conduct Disorder in Young Children. A Case Report  [PDF]
Hadia Crider, Kunal Malhotra, Garima Singh
Journal of Biosciences and Medicines (JBM) , 2018, DOI: 10.4236/jbm.2018.62005
Abstract: Childhood Onset Conduct Disorder [CD] is a condition characterized by at least one symptom of conduct disorder (based on Diagnostic and Statistical Manual of Mental Disorders criteria—Fifth Edition) prior to 10 years of age. Children affected exhibit disruptive behaviors, usually negative, hostile, and defiant behavior similar to Oppositional Defiant Disorder [ODD]. As the child gets older they begin to display more characteristic of Conduct Disorder (lying, fighting, and stealing, vindictive behavior). These children are also likely to have comorbidities including Attention Deficit Hyperactivity Disorder (ADHD), learning disabilities, poor academic achievement, and substance abuse. Distinguishing early between symptoms of Conduct Disorder versus other differential diagnoses is essential in effective treatment. Early intervention with these children leads to a better prognosis and likelihood of functioning in society. This case illustrates the difficulty of diagnosing a young child with Childhood Onset Conduct Disorder.
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