Multicollinearity

in Chow, Shein-Chung (Ed.) Encyclopedia of Biopharmaceutical Statistics (2004)

Deficient host-bacteria interactions in inflammatory bowel disease? The toll-like receptor (TLR)-4 Asp299gly polymorphism is associated with Crohn's disease and ulcerative colitis

in Gut (2004), 53(7), 987-992

Background and aims: Elicitation of an innate immune response to bacterial products is mediated through pattern recognition receptors (PRRs) such as the toll-like receptors (TLRs) and the NODs. The ... [more ▼]

Background and aims: Elicitation of an innate immune response to bacterial products is mediated through pattern recognition receptors (PRRs) such as the toll-like receptors (TLRs) and the NODs. The recently characterised Asp299Gly polymorphism in the lipopolysaccharide (LPS) receptor TLR4 is associated with impaired LPS signalling and increased susceptibility to Gram negative infections. We sought to determine whether this polymorphism was associated with Crohn's disease ( CD) and/or ulcerative colitis (UC). Methods: Allele frequencies of the TLR4 Asp299Gly polymorphism and the three NOD2/CARD15 polymorphisms (Arg702Trp, Gly908Arg, and Leu1007fsinsC) were assessed in two independent cohorts of CD patients ( cohort 1, n = 334; cohort 2, n = 114), in 163 UC patients, and in 140 controls. A transmission disequilibrium test (TDT) was then performed on 318 inflammatory bowel disease (IBD) trios. Results: The allele frequency of the TLR4 Asp299Gly polymorphism was significantly higher in CD ( cohort 1: 11% v 5%, odds ratio ( OR) 2.31 (95% confidence interval (CI) 1.28 - 4.17), p = 0.004; and cohort 2: 12% v 5%, OR 2.45 ( 95% CI 1.24 - 4.81), p = 0.007) and UC patients (10% v 5%, OR 2.05 ( 95% CI 1.07 3.93), p = 0.027) compared with the control population. A TDT on 318 IBD trios demonstrated preferential transmission of the TLR4 Asp299Gly polymorphism from heterozygous parents to affected children (T/U: 68/34, p = 0.01). Carrying polymorphisms in both TLR4 and NOD2 was associated with a genotype relative risk (RR) of 4.7 compared with a RR of 2.6 and 2.5 for TLR4 and NOD2 variants separately. Conclusion: We have reported on a novel association of the TLR4 Asp299Gly polymorphism with both CD and UC. This finding further supports the genetic influence of PRRs in triggering IBD. [less ▲]

Interassay and interobserver variability in the detection of anti-neutrophil cytoplasmic antibodies in patients with ulcerative colitis.

in Clinical Chemistry (2004), 50(8), 1422-5

Autoimmunity associated with anti-tumor necrosis factor alpha treatment in Crohn's disease: A prospective cohort study

in Gastroenterology (2003), 125(1), 32-39

Background & Aims: Infliximab therapy is an effective approach to treating Crohn's disease. Development of antinuclear antibodies has been described in patients treated, but the size of the problem and ... [more ▼]

Background & Aims: Infliximab therapy is an effective approach to treating Crohn's disease. Development of antinuclear antibodies has been described in patients treated, but the size of the problem and the relationship with autoimmunity have not been investigated. We investigated the occurrence of antinuclear antibodies in 125 consecutive Crohn's disease patients and studied the relationship with symptoms of autoimmunity. Methods: Autoantibodies and clinical data were investigated before and 1, 2, and 3 months after infliximab infusion. If antinuclear antibodies were greater than or equal to1:80, further study of double-stranded DNA, single-stranded DNA, histones, and ENA was performed. Results: Cumulative antinuclear antibody incidence at 24 months was 71 of 125 (56.8%). Almost half of these patients developed antinuclear antibodies after the first infusion, and >75% became antinuclear antibody positive after fewer than 3 infusions. So far, only :15 of 71 patients have become seronegative, after a median of 12 months. Of 43 antinuclear antibody-positive patients who were further subtyped, 14 of 43 (32.6%) had double-stranded DNA, 17 (39.5%) had single-stranded DNA, 9 (20.9%) had antihistone, and 0% were ENA positive. Two patients (both antihistone and double-stranded DNA positive) developed drug-induced lupus without major organ damage, and I developed autoimmune hemolytic anemia. Antinuclear antibodies were associated with the female sex (odds ratio, 3.166; 95% confidence interval, 1.167-8.585; P = 0.024) and with papulosquamous or butterfly rash (odds ratio, 10.016; 95% confidence interval, 1.708-58.725; P = 0.011). Conclusions: The cumulative incidence of antinuclear antibodies was 56.8% after 24 months in this cohort of infliximab-treated Crohn's disease patients. Antinuclear antibodies persisted up to I year after the last infusion, and only a few patients became seronegative. Two patients developed drug-induced lupus erythematosus. Antinuclear antibodies were associated with the female sex and skin manifestations. [less ▲]

A local influence approach applied to binary data from a psychiatric study.

in Biometrics (2003), 59(2), 410-9

Recently, a lot of concern has been raised about assumptions needed in order to fit statistical models to incomplete multivariate and longitudinal data. In response, research efforts are being devoted to ... [more ▼]

Recently, a lot of concern has been raised about assumptions needed in order to fit statistical models to incomplete multivariate and longitudinal data. In response, research efforts are being devoted to the development of tools that assess the sensitivity of such models to often strong but always, at least in part, unverifiable assumptions. Many efforts have been devoted to longitudinal data, primarily in the selection model context, although some researchers have expressed interest in the pattern-mixture setting as well. A promising tool, proposed by Verbeke et al. (2001, Biometrics 57, 43-50), is based on local influence (Cook, 1986, Journal of the Royal Statistical Society, Series B 48, 133-169). These authors considered the Diggle and Kenward (1994, Applied Statistics 43, 49-93) model, which is based on a selection model, integrating a linear mixed model for continuous outcomes with logistic regression for dropout. In this article, we show that a similar idea can be developed for multivariate and longitudinal binary data, subject to nonmonotone missingness. We focus on the model proposed by Baker, Rosenberger, and DerSimonian (1992, Statistics in Medicine 11, 643-657). The original model is first extended to allow for (possibly continuous) covariates, whereafter a local influence strategy is developed to support the model-building process. The model is able to deal with nonmonotone missingness but has some limitations as well, stemming from the conditional nature of the model parameters. Some analytical insight is provided into the behavior of the local influence graphs. [less ▲]

Multivariate and multidimensional analysis

in Wilson (Ed.) Biometrics (2003)

The multivariate Dale model and genetic associations

in American Journal of Human Genetics (2002), 71

Merits of the multivariate Dale model in genetic association studies

in Genetic Epidemiology (2002), 23

Human recombinant erythropoietin and quality of life: a wonder drug or something to wonder about?

in Lancet Oncology (2002), 3(3), 145-53

Over the past decade an increasing number of studies have supported the use of recombinant human erythropoietin (epoetin) in cancer patients, suggesting that it improves haemoglobin concentrations for ... [more ▼]

Over the past decade an increasing number of studies have supported the use of recombinant human erythropoietin (epoetin) in cancer patients, suggesting that it improves haemoglobin concentrations for some. There is also evidence that this treatment may lead to improvement in quality of life for cancer patients. This systematic review examines the issue. We identified and critically reviewed 13 trials. Although some of the results indicate that epoetin has positive effects on quality of life, methodological limitations inherent in most of the studies hamper interpretation of data. Evidence from this review suggests that more robust designs are required to show any significant quality-of-life benefits for cancer patients undergoing epoetin treatment. [less ▲]

The value of serologic markers in indeterminate colitis: A prospective follow-up study

in Gastroenterology (2002), 122(5), 1242-1247