Applied causal inference methods for sequential mediators.

BACKGROUND: Mediation analysis aims at estimating to what extent the effect of an exposure on an outcome is explained by a set of mediators on the causal pathway between the exposure and the outcome. The total effect of the exposure on the outcome can be decomposed into an indirect effect, i.e. the effect explained by the mediators jointly, and a direct effect, i.e. the effect unexplained by the mediators. However finer decompositions are possible in presence of independent or sequential mediators. METHODS: We review four statistical methods to analyse multiple sequential mediators, the inverse odds ratio weighting approach, the inverse probability weighting approach, the imputation approach and the extended imputation approach. These approaches are compared and implemented using a case-study with the aim to investigate the mediating role of adverse reproductive outcomes and infant respiratory infections in the effect of maternal pregnancy mental health on infant wheezing in the Ninfea birth cohort. RESULTS: Using the inverse odds ratio weighting approach, the direct effect of maternal depression or anxiety in pregnancy is equal to a 59% (95% CI: 27%,94%) increased prevalence of infant wheezing and the mediated effect through adverse reproductive outcomes is equal to a 3% (95% CI: -6%,12%) increased prevalence of infant wheezing. When including infant lower respiratory infections in the mediation pathway, the direct effect decreases to 57% (95% CI: 25%,92%) and the indirect effect increases to 5% (95% CI: -5%,15%). The estimates of the effects obtained using the weighting and the imputation approaches are similar. The extended imputation approach suggests that the small joint indirect effect through adverse reproductive outcomes and lower respiratory infections is due entirely to the contribution of infant lower respiratory infections, and not to an increased prevalence of adverse reproductive outcomes. CONCLUSIONS: The four methods revealed similar results of small mediating role of adverse reproductive outcomes and early respiratory tract infections in the effect of maternal pregnancy mental health on infant wheezing. The choice of the method depends on what is the effect of main interest, the type of the variables involved in the analysis (binary, categorical, count or continuous) and the confidence in specifying the models for the exposure, the mediators and the outcome.

Natural history of naevi: a two-wave study.

BACKGROUND: Naevi number changes with age. Thus, a better understanding of naevus biology will shed more light on the genetic and environmental factors involved in melanoma development. OBJECTIVES: To use a two-wave study to better understand the evolution of naevi in healthy adults. METHODS: This study is a prospective two-wave study based on adult twins from the TwinsUK registry (n = 414) who underwent total body naevus counts with an interval of at least 15 years. A negative binomial hierarchical model with two levels, the individual and the twin pair, was used to estimate expected changes in naevus count between the first and second visit, at any specific body site and on the whole body. The model was adjusted for age, calendar year at the first visit, height and skin type. RESULTS: The mean age of participants was 46 years at the first visit and 63 years at the second visit (the mean elapsed time between visits was 17 years). An increase in naevus count was observed in 235 (57%) participants and a decrease was observed in 166 (40%). The mean difference in total naevus count between the two visits was nine. The expected total body naevus count increased, on a logarithmic scale, by 0·28 [95% confidence interval (CI) 0·16-0·40] with a change in the incidence rate of total body naevus count of 32% (95% CI 17-49%). However, the observed increase in naevus count over time was observed only on the upper parts of the body, whereas there was no evidence of an increase on the lower parts. CONCLUSIONS: Naevus counts increased slightly over time at older ages, but this was dependent on body site. The overall decrease in naevus counts previously reported in cross-sectional studies has not been confirmed by this longitudinal study.

Maternal anxiety, depression and sleep disorders before and during pregnancy, and preschool ADHD symptoms in the NINFEA birth cohort study.

AIMS.: Maternal mental disorders have been associated with the risk of attention-deficit/hyperactivity disorder (ADHD) in children. Within the context of a mother-child cohort, we examined whether maternal anxiety, depression and sleep disorders are associated with pre-school ADHD symptoms. METHODS.: The study included 3634 singletons from the Italian NINFEA (Nascita e INFanzia: gli Effetti dell'Ambiente') cohort. Maternal doctor-diagnosed anxiety, depression and sleep disorders before and during pregnancy were assessed from the questionnaires completed during pregnancy and 6 months after delivery. Mothers rated child ADHD symptoms at 4 years of age, according to the Diagnostic and Statistical Manual of Mental Disorders. Hyperactive-impulsive (ADHD-H), inattentive (ADHD-I) and total ADHD scores were analysed in the models adjusted for child's gender, first-born status, maternal age, education, alcohol consumption and smoking during pregnancy. RESULTS.: The total ADHD score at age 4 was associated with maternal lifetime anxiety (17.1% percentage difference in score compared with never; 95% CI 7.3-27.9%), sleep disorders (35.7%; 95% CI 10.7-66.5%) and depression (17.5%; 95% CI 3.2-33.8%). Similar positive associations were observed also for ADHD-H and ADHD-I traits, with slightly attenuated associations between maternal sleep disorders and child ADHD-I score, and maternal depression and both ADHD scores. All the estimates were enhanced when the disorders were active during pregnancy and attenuated for disorders active only during the pre-pregnancy period. CONCLUSIONS.: Maternal anxiety, depression and sleep disorders are associated with a relative increase in the number of ADHD-H, ADHD-I and total ADHD symptoms in preschoolers.

Sources of confounding in life course epidemiology.

In epidemiologic analytical studies, the primary goal is to obtain a valid and precise estimate of the effect of the exposure of interest on a given outcome in the population under study. A crucial source of violation of the internal validity of a study involves bias arising from confounding, which is always a challenge in observational research, including life course epidemiology. The increasingly popular approach of meta-analyzing individual participant data from several observational studies also brings up to discussion the problem of confounding when combining data from different populations. In this study, we review and discuss the most common sources of confounding in life course epidemiology: (i) confounding by indication, (ii) impact of baseline selection on confounding, (iii) time-varying confounding and (iv) mediator-outcome confounding. We also discuss the issue of addressing confounding in the context of an individual participant data meta-analysis.

Tenofovir disoproxil fumarate discontinuation for renal outcomes: any room for treatment personalization?

Tenofovir disoproxil fumarate (TDF) is a very effective antiviral drug that has been associated with tubular dysfunction. The aim of this study was to analyze the demographic, pharmacokinetic, and pharmacogenetic variables associated with TDF discontinuation for renal outcomes in stable HIV-positive patients using multivariable analyses. Three hundred and four patients were included (73% male, with median age and eCrCl of 45.3 years and 90.9 mL/min, respectively). After a median follow-up of 28.3 months, 27 patients discontinued TDF for renal adverse events [persistent urinary abnormalities (n = 21) or eCrCl < 60 mL/min (n = 6)] providing an incidence of 3.77 events per 100 patient-year. The probability of TDF discontinuation was higher with several features (male gender, older age, not Caucasians ancestry, absence of intravenous drug abuse, protease inhibitors, previous indinavir, HCV-positivity, lower CD4 cell count, detectable HIV-RNA, lower eCrCl, spot-urine proteinuria) and higher tenofovir concentrations but not genetic variants. Tenofovir plasma concentrations were prognostic of TDF discontinuation for renal adverse events suggesting that dose-adjustment may be warranted for long-term safety.

Favourable prognostic role of histological regression in stage III positive sentinel lymph node melanoma patients.

BACKGROUND: Sentinel lymph node (SLN)-positive melanoma patients are a heterogeneous group of patients with survival rates ranging from ∼20 to over 80%. No data are reported concerning the role of histological regression on survival in stage III melanoma. METHODS: The study included 365 patients with positive SLN from two distinct hospitals. The model was developed on patients from 'AOU Città della Salute e della Scienza di Torino', and externally validated on patients from IRCCS of Candiolo. Survival analyses were carried out according to the presence of regression and adjusted for all other prognostic factors. RESULTS: Among patients followed at 'AOU Città della Salute e della Scienza di Torino' (n=264), the median follow-up time to death or censoring (whatever two events occurred earlier) was 2.7 years since diagnosis (interquartile range: 1.3-5.8). In all, 79 patients died from melanoma and 11 from other causes. Histological regression (n=43) was associated with a better prognosis (sub-HR=0.34, CI 0.12-0.92), whereas the other factors above showed an inverse association. In the external validation, the concordance index was 0.97 at 1 year and decreased to 0.66 at 3 years and to 0.59 at 5 years. Adding histological regression in the prognostic model increased the discriminative ability to 0.75 at 3 years and to 0.62 at 5 years. Finally, using a cutoff of 20% for the risk of death led to a net re-classification improvement of 15 and 11% at 3 and 5 years after diagnosis, respectively. CONCLUSIONS: Histological regression could lead to an improvement in prognostic prediction in patients with stage III-positive SLN melanoma.

Baldness and testicular cancer: the EPSAM case-control study.

The etiology of testicular cancer is largely unexplained. Research has mainly focused on prenatal exposures, especially to sex hormones, while less attention has been paid to exposures that may act also postnatally. As baldness has been previously associated with testicular cancer risk we focused on baldness and body hairiness, which are both associated with androgen activity. We used data of the Postnatal Exposures and Male Health (EPSAM) study, a case-control study on testicular cancer conducted in the Province of Turin, Italy, involving cases diagnosed between 1997 and 2008. Information was collected using mailed questionnaires. Analyses included 255 cases and 459 controls. We calculated ORs and 95% CIs to estimate testicular cancer risk among those who developed baldness and among those with body hairiness. We found an inverse association between testicular cancer and baldness (OR: 0.67, 95% CI: 0.46-0.98) and body hairiness (OR: 0.78, 95% CI: 0.53-1.16), although the latter had wider CIs. The inverse association between baldness and testicular cancer is consistent with the results from previous studies. These results suggest that androgens activity may influence testicular cancer risk.

The independent role of prenatal and postnatal exposure to active and passive smoking on the development of early wheeze in children.

Maternal smoking during pregnancy increases childhood asthma risk, but health effects in children of nonsmoking mothers passively exposed to tobacco smoke during pregnancy are unclear. We examined the association of maternal passive smoking during pregnancy and wheeze in children aged ≤2 years.Individual data of 27 993 mother-child pairs from 15 European birth cohorts were combined in pooled analyses taking into consideration potential confounders.Children with maternal exposure to passive smoking during pregnancy and no other smoking exposure were more likely to develop wheeze up to the age of 2 years (OR 1.11, 95% CI 1.03-1.20) compared with unexposed children. Risk of wheeze was further increased by children's postnatal passive smoke exposure in addition to their mothers' passive exposure during pregnancy (OR 1.29, 95% CI 1.19-1.40) and highest in children with both sources of passive exposure and mothers who smoked actively during pregnancy (OR 1.73, 95% CI 1.59-1.88). Risk of wheeze associated with tobacco smoke exposure was higher in children with an allergic versus nonallergic family history.Maternal passive smoking exposure during pregnancy is an independent risk factor for wheeze in children up to the age of 2 years. Pregnant females should avoid active and passive exposure to tobacco smoke for the benefit of their children's health.

Prediction of high naevus count in a healthy U.K. population to estimate melanoma risk.

BACKGROUND: Despite recent discoveries of germline and somatic mutations in melanoma, naevus count remains the most important risk factor for melanoma. Counting naevi on the whole body is time consuming. In order to identify patients at risk for melanoma, many studies have used naevus count on selected body sites as a proxy for total body naevus count (TBNC). OBJECTIVES: The main aim of this study was to assess the predictive value of naevus count on 17 different body sites in estimating TBNC in a large cohort of healthy U.K. Caucasian female subjects. Once the site with the best predictive value for TBNC was determined, a second aim was to estimate the cut-off values of naevus counts at this anatomical site that best predict the presence of 50 or 100 naevi, respectively. METHODS: The most predictive body site for TBNC was assessed in a cohort of healthy female twins. This finding was replicated on a control group from a U.K. case-control study and a prediction model was performed afterwards. The area under the receiver operating characteristics curve was used to evaluate the best cut-off for the prediction of having a TBNC of more than 50 or 100. RESULTS: There were 3694 female twins included. The TBNC showed a steady decline after the age of 30 years (P < 0·001). The most predictive sites for TBNC were the arms and legs: the adjusted correlation coefficients were 0·50 and 0·51 (P < 0·001) for the right and left arm, respectively, and 0·49 and 0·48 for the right and left legs, respectively (P < 0·001). The arm remained the most predictive site for TBNC when replicated in a control population including both sexes. In the twin study, women with more than 11 naevi on the right arm were approximately nine times more likely to have more than 100 naevi (odds ratio = 9·38, 95% confidence interval 6·71-13·11). CONCLUSIONS: The ability to estimate TBNC quickly by counting naevi on one arm could be a very useful tool in assessing melanoma risk in primary care.

Global DNA hypomethylation in prostate cancer development and progression: a systematic review.

BACKGROUND: The role of global DNA methylation in prostate cancer (PCa) remains largely unknown. Our aim was to summarize evidence on the role of global DNA hypomethylation in PCa development and progression. METHODS: We searched PubMed through December 2013 for all studies containing information on global methylation levels in PCa tissue and at least one non-tumor comparison tissue and/or studies reporting association between global methylation levels in PCa tissue and survival, disease recurrence or at least one clinicopathological prognostic factor. We summarized results using non-parametric comparisons and P-value summary methods. RESULTS: We included 15 studies in the review: 6 studies with both diagnostic and prognostic information, 5 studies with only diagnostic information and 4 studies with only prognostic information. Quantitative meta-analysis was not possible because of the large heterogeneity in molecular techniques, types of tissues analyzed, aims and study designs. Summary statistical tests showed association of DNA hypomethylation with PCa diagnosis (P<0.006) and prognosis (P<0.001). Restriction to studies assessing 5-methylcytosine or long interspersed nucleotide element-1 revealed results in the same direction. Analyses restricted to specific clinicopathological features showed association with the presence of metastasis and tumor stage in all tests with P<0.03, and no association with Gleason score (all tests P>0.1 except for the weighted Z-test, P=0.05). CONCLUSION: DNA hypomethylation was associated with PCa development and progression. However, due to the heterogeneity and small sample sizes of the included studies, along with the possibility of publication bias, this association requires additional assessment.