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J Whitton

Publications and source records attributed to J Whitton.

8 recordsLinked to original sources
PubMed2001

CYP2C9 and UGT1A6 genotypes modulate the protective effect of aspirin on colon adenoma risk.

Regular use of nonsteroidal anti-inflammatory drugs (NSAIDs) has a protective effect on the incidence of colon neoplasia. However, polymorphisms in NSAID-metabolizing enzymes may alter this effect. NSAIDs, particularly aspirin, are glucuronidated by UGT1A6 and some classes of NSAIDs are also metabolized by cytochrome P450 (CYP) 2C9. Both of these enzymes have slow-metabolizing, variant forms. We tested the hypothesis that the slow alleles of these enzymes can modify the inverse association between NSAIDs and colon neoplasia in the Minnesota Cancer Prevention Research Unit (CPRU) adenomatous polyp case-control study. CYP2C9 and UGT1A6 genotypes were determined for 474 adenoma cases and 563 controls. NSAID use was inversely associated with adenoma risk [odds ratio (OR), 0.63; 95% confidence interval (CI), 0.44-0.90 for aspirin; and OR, 0.50; 95% CI, 0.31-0.82 for nonaspirin NSAID]. However, this association was absent in aspirin users who carried the CYP2C9 variant alleles (OR, 0.88; 95% CI, 0.51-1.53) or who were homozygous wild-type UGT1A6 (OR, 0.86; 95% CI, 0.50-1.50). Carriers of both of these alleles who use aspirin were also not at reduced risk of adenomatous polyps (OR, 1.59; 95% CI, 0.68-3.73). The variants of these enzymes did not influence the association between nonaspirin NSAIDs and adenoma risk. These data indicate that the effectiveness of chemopreventive drugs can be modulated by the genotype of metabolizing enzymes.

Adenoma↗
PubMed2000

Polyploid incidence and evolution.

Changes in ploidy occurred early in the diversification of some animal and plant lineages and represent an ongoing phenomenon in others. While the prevalence of polyploid lineages indicates that this phenomenon is a common and successful evolutionary transition, whether polyploidization itself has a significant effect on patterns and rates of diversification remains an open question. Here we review evidence for the creative role of polyploidy in evolution. We present new estimates for the incidence of polyploidy in ferns and flowering plants based on a simple model describing transitions between odd and even base chromosome numbers. These new estimates indicate that ploidy changes may represent from 2 to 4% of speciation events in flowering plants and 7% in ferns. Speciation via polyploidy is likely to be one of the more predominant modes of sympatric speciation in plants, owing to its potentially broad-scale effects on gene regulation and developmental processes, effects that can produce immediate shifts in morphology, breeding system, and ecological tolerances. Theoretical models support the potential for increased adaptability in polyploid lineages. The evidence suggests that polyploidization can produce shifts in genetic systems and phenotypes that have the potential to result in increased evolutionary diversification, yet conclusive evidence that polyploidy has changed rates and patterns of diversification remains elusive.

Animals↗
PubMed2000

Abnormalities of the thyroid in survivors of Hodgkin's disease: data from the Childhood Cancer Survivor Study.

Treatment for Hodgkin's disease (HD) is associated with a variety of thyroid abnormalities, including hypothyroidism, hyperthyroidism, and thyroid neoplasms. Due to the small sample size and short follow-up time of most published studies, it has been difficult to appreciate the full extent of the problem and to characterize the interaction between various patient and treatment variables. To overcome these limitations we have assessed thyroid status in 1,791 (959 males) HD survivors from among 13,674 participants in the Childhood Cancer Survivor Study, a cohort of 5-yr survivors of childhood and adolescent cancer diagnosed between 1970 and 1986. Thyroid abnormalities were ascertained as part of a 22-page questionnaire sent to participants. Survivors were a median of 14 yr (range, 2-20 yr) at diagnosis of HD and a median of 30 yr (range, 12-47 yr) at follow-up. Seventy-nine percent of subjects were treated with radiation (median dose of radiation to the thyroid, 3,500 cGy; range, 0.37-5,500 cGy). Control data were available from 2,808 (1,346 males) sibling controls. Thirty-four percent of the entire cohort has been diagnosed with at least one thyroid abnormality. Hypothyroidism was the most common disturbance, with a relative risk of 17.1 (P < 0.0001) compared to sibling controls. Increasing dose of radiation, older age at diagnosis of HD, and female sex were all independently associated with an increased risk of hypothyroidism. Actuarial risk of hypothyroidism for subjects treated with 4,500 cGy or more is 50% at 20 yr from diagnosis. Hyperthyroidism was reported by 5% of survivors, which was 8-fold greater (P < 0.0001) than the incidence reported by the controls. Thyroid dose of 3,500 cGy or more was the only risk factor identified for hyperthyroidism. The risk of thyroid nodules was 27 times (P < 0.0001) that in sibling controls. Female sex and radiation dose to the thyroid of 2,500 cGy or more were independent risk factors for thyroid nodules. The actuarial risk of a female survivor developing a thyroid nodule is 20% at 20 yr from diagnosis. Thyroid cancer was diagnosed in 20 survivors, which is 18 times the expected rate for the general population. After taking into account the possibility that some of the relative risk estimates may be exaggerated due to ascertainment bias, abnormalities of the thyroid are still extremely common in young adult survivors of childhood HD, particularly among females treated with high doses of radiation to the neck.

Adolescent↗
PubMed1999

Problems in using age-stratum-specific reference rates for indirect standardization.

Disease risk in a study cohort can be compared with that in a reference population using the method of indirect standardization, adjusting for a difference in age distribution between the cohort and reference population. The common epidemiological practice is to use categorical age, typically in the form of 5-year age strata, in the standardization. This article discusses problems that arise owing to the categorization of age, including biased estimation and incorrect statistical inference on relative risk parameters. The same problems further extend to more general analyses using Poisson regression. We illustrate the problems using a hypothetical example and propose a simple remedy using linear splines. A slightly more elaborate method and its computer program are given in the appendix.

Age Distribution↗
PubMed1999

Hybrid zones and the genetic architecture of a barrier to gene flow between two sunflower species.

Genetic analyses of reproductive barriers represent one of the few methods by which theories of speciation can be tested. However, genetic study is often restricted to model organisms that have short generation times and are easily propagated in the laboratory. Replicate hybrid zones with a diversity of recombinant genotypes of varying age offer increased resolution for genetic mapping experiments and expand the pool of organisms amenable to genetic study. Using 88 markers distributed across 17 chromosomes, we analyze the introgression of chromosomal segments of Helianthus petiolaris into H. annuus in three natural hybrid zones. Introgression was significantly reduced relative to neutral expectations for 26 chromosomal segments, suggesting that each segment contains one or more factors that contribute to isolation. Pollen sterility is significantly associated with 16 of these 26 segments, providing a straightforward explanation of why this subset of blocks is disadvantageous in hybrids. In addition, comparison of rates of introgression across colinear vs. rearranged chromosomes indicates that close to 50% of the barrier to introgression is due to chromosomal rearrangements. These results demonstrate the utility of hybrid zones for identifying factors contributing to isolation and verify the prediction of increased resolution relative to controlled crosses.

Alleles↗
PubMed1992

Electrotherapy and the management of minimally displaced fracture of the neck of the humerus.

A poor outcome arising from a minimally displaced fracture of the neck of the humerus may be the result of a contracture of the capsule of the glenohumoral joint. Pulsed high frequency electromagnetic energy (PHFE) is an electrotherapy to reduce pain and swelling and to enhance healing. If PHFE is effective, early mobilization of the injured shoulder will be possible, reducing the risk of joint capsule contracture. We therefore conducted a double-blind trial of PHFE in minimally displaced fractures of the neck of the humerus. Early physiotherapy produced an excellent outcome in all cases. The functional outcome depended on age rather than time of starting treatment, although a relationship was found between the time of starting treatment and the duration of therapy required. The use of PHFE did not improve the result further.

Adolescent↗