Melanocortin-1 receptor, skin cancer and phenotypic characteristics (M-SKIP) project: study design and methods for pooling results of genetic epidemiological studies

Background

For complex diseases like cancer, pooled-analysis of individual data represents a powerful tool to investigate the joint contribution of genetic, phenotypic and environmental factors to the development of a disease. Pooled-analysis of epidemiological studies has many advantages over meta-analysis, and preliminary results may be obtained faster and with lower costs than with prospective consortia.

Design and methods

Based on our experience with the study design of the Melanocortin-1 receptor (MC1R) gene, SKin cancer and Phenotypic characteristics (M-SKIP) project, we describe the most important steps in planning and conducting a pooled-analysis of genetic epidemiological studies. We then present the statistical analysis plan that we are going to apply, giving particular attention to methods of analysis recently proposed to account for between-study heterogeneity and to explore the joint contribution of genetic, phenotypic and environmental factors in the development of a disease. Within the M-SKIP project, data on 10,959 skin cancer cases and 14,785 controls from 31 international investigators were checked for quality and recoded for standardization. We first proposed to fit the aggregated data with random-effects logistic regression models. However, for the M-SKIP project, a two-stage analysis will be preferred to overcome the problem regarding the availability of different study covariates. The joint contribution of MC1R variants and phenotypic characteristics to skin cancer development will be studied via logic regression modeling.

Discussion

Methodological guidelines to correctly design and conduct pooled-analyses are needed to facilitate application of such methods, thus providing a better summary of the actual findings on specific fields.

Prevalence and concurrence of anxiety, depression and fatigue over time in multiple sclerosis

BACKGROUND

Anxiety, depression and fatigue are commonly reported by persons with multiple sclerosis (PwMS).

OBJECTIVES

We estimated the prevalence of each factor in a representative sample of PwMS, and in subgroups defined by age, sex and disease duration, at cohort entry and over time. We further examined whether and how these factors clustered together.

METHODS

A population-based longitudinal cohort of 198 PwMS was followed 6-monthly for 2.5 years. The Hospital Anxiety and Depression Scale (HADS) was used to measure anxiety (cut-point >7) and depression (>7) and the Fatigue Severity Scale (FSS) to measure fatigue (≥5).

RESULTS

At cohort entry, prevalence of anxiety was 44.5% (95%CI 37-51%), depression 18.5% (95%CI 12.6-23.4%), and fatigue 53.7% (95%CI 47-61%). Fatigue was more common in males than females (RR 1.29, p=0.01), with attenuation of the effect after adjustment for Expanded Disability Status Scale (adjusted RR 1.18, p=0.13). Prevalence of anxiety (but not depression or fatigue) decreased by 8.1% per year of cohort observation (RR 0.92, 95%CI 0.86-0.98, p=0.009), with the effect more pronounced in women (14.6%, RR 0.85, 95%CI 0.79-0.93, -<0.001) than men (2.6%, RR 1.03, 95%CI 0.90-1.17, p=0.77). There was no apparent seasonal variation in the prevalence of any of the three factors (p>0.05). All three factors occurred contemporaneously at cohort entry in a higher proportion of the cohort than expected by chance (p<0.001).

CONCLUSIONS

Anxiety, depression and fatigue are common in PwMS and tend to cluster together. The findings are important for clinical management of PwMS and to the exploration of possible shared causal biological pathways.

Offspring number, pregnancy, and risk of a first clinical demyelinating event: the AusImmune Study

OBJECTIVE

To examine the association between past pregnancy, offspring number, and first clinical demyelination risk.

METHODS

Cases (n = 282) were aged 18-59 years with a first clinical diagnosis of CNS demyelination (first clinical demyelinating event [FCD]) and resident within 1 of 4 Australian centers (from latitudes 27° south to 43° south) from 2003 to 2006. Controls (n = 542) were matched to cases on age, sex, and study region, without first clinical diagnosis of CNS demyelination.

RESULTS

Higher offspring number was associated with FCD risk among women (p < 0.001) but not men (p = 0.71); difference in effect; p = 0.001. Among women, higher parity was associated with reduced risk of FCD (adjusted odds ratio 0.51 [95% confidence interval 0.36, 0.72] per birth) with a similar magnitude of effect observed among classic first demyelinating events (adjusted odds ratio 0.47 [95% confidence interval 0.29, 0.74]). The apparent beneficial effect of higher parity was also evident among parous women only (p < 0.001). Among cases, a clear female excess was evident for those with low but not high (4 or more) offspring number. Factors such as human leukocyte antigen DR15 genotype did not appear to modify the association between higher parity and a reduced FCD risk among women.

CONCLUSIONS

These findings are consistent with a cumulative beneficial effect of pregnancy. Temporal changes toward an older maternal age of parturition and reduced offspring number may partly underlie the increasing female excess among MS cases over time.

Maternal and infant factors associated with neonatal adiposity: results from the Tasmanian Infant Health Survey (TIHS)

OBJECTIVE

To examine the maternal and neonatal factors associated with offspring adiposity and the role of birth and placental weight as potential mediators in such associations.

DESIGN

The Tasmanian Infant Health Survey was a prospective cohort study conducted between 1988 and 1995 in Australia to investigate the cause of Sudden Infant Death Syndrome. This large infant cohort provides measurement of skinfolds on 7945 mothers and their offspring.

SUBJECTS

Participants included singletons born ≥37 weeks gestation who were at high risk of sudden infant death syndrome identified through a composite score that included birth weight, maternal age, neonatal gender, season of birth, duration of second-stage labor and intention to breastfeed.

MEASUREMENTS

Neonatal adiposity was assessed from skinfold measurements of the subscapular (SSF) and triceps folds (TSF) taken at birth. Maternal early-pregnancy body mass index (BMI) was calculated from self-reported height and weight. Neonatal data were extracted from birth records. Data relating to other environmental exposures were obtained from questionnaires administered when neonates were ∼4-days old.

RESULTS

In multivariable models, higher maternal adiposity, increasing maternal age, gestation age, delivery by Caesarian section and female gender were associated with larger SSF independent of placental and birth weight (P<0.001). Maternal age and delivery by Caesarian section were significantly associated with larger TSF, whereas gestational age and male gender were associated with thinner TSF independent of placental and birth weight. Higher early-pregnancy BMI, maternal weight gain, maternal age, parity and gestational age were significantly associated with larger placental and birth weight. Smoking during pregnancy was associated with smaller birth weight but not with placental weight.

CONCLUSION

In addition to birth weight, maternal adiposity and placental weight were important additional factors associated with neonatal adiposity.

Takeaway food consumption and cardio-metabolic risk factors in young adults

BACKGROUND/OBJECTIVES

Takeaway food consumption is positively associated with adiposity. Little is known about the associations with other cardio-metabolic risk factors. This study aimed to determine whether takeaway food consumption is associated with fasting glucose, insulin, lipids, homeostasis model assessment (HOMA) and blood pressure.

SUBJECTS/METHODS

A national sample of 1896, 26-36 year olds completed a questionnaire on socio-demographics, takeaway food consumption, physical activity and sedentary behaviour. Waist circumference and blood pressure were measured, and a fasting blood sample was taken. For this analysis, takeaway food consumption was dichotomised to once a week or less and twice a week or more. Linear regression was used to calculate differences in the adjusted mean values for fasting lipids, glucose, insulin, HOMA and blood pressure. Models were adjusted for age, employment status, leisure time physical activity and TV viewing.

RESULTS

Compared with women who ate takeaway once a week or less, women who ate takeaway twice a week or more had significantly higher adjusted mean fasting glucose (4.82 vs 4.88 mmol/l, respectively; P=0.045), higher HOMA scores (1.27 vs 1.40, respectively, P=0.034) and tended to have a higher mean fasting insulin (5.95 vs 6.45 mU/l, respectively, P=0.054). Similar associations were observed for men for fasting insulin and HOMA score, but the differences were not statistically significant. For both women and men adjustment for waist circumference attenuated the associations.

CONCLUSION

Consuming takeaway food at least twice a week was associated with cardio-metabolic risk factors in women but less so in men. The effect of takeaway food consumption was attenuated when adjusted for obesity.

Iodine status in late pregnancy and psychosocial determinants of iodized salt use in rural northern Viet Nam

OBJECTIVE

To establish iodine status among pregnant women in rural northern Viet Nam and explore psychosocial predictors of the use of iodized salt in their households.

METHODS

This prospective study included pregnant women registered in health stations in randomly-selected communes in Ha Nam province. At recruitment (< 20 weeks of gestation), sociodemographic factors, reproductive health, intimate partner relationship, family violence, symptoms of common mental disorders and use of micronutrient supplements were assessed. During a second assessment (> 28 weeks of gestation) a urine specimen was collected to measure urinary iodine concentration (UIC) and iodized salt use was assessed. Predictors were explored through univariable analyses and multivariable linear and logistic regression.

FINDINGS

The 413 pregnant women who provided data for this study had a median UIC of 70 µg/l; nearly 83% had a UIC lower than the 150 µg/l recommended by the World Health Organization; only 73.6% reported using iodized salt in any form in their households. Iodized salt use was lower among nulliparous women (odds ratio, OR: 0.56; 95% confidence interval, CI: 0.32-0.96); less educated women (OR: 0.34; 95% CI: 0.16-0.71); factory workers or small-scale traders (OR: 0.52; 95% CI: 0.31-0.86), government workers (OR: 0.35; 95% CI: 0.13-0.89) and women with common mental disorders at recruitment (OR: 0.61; 95% CI: 0.38-0.98).

CONCLUSION

The decline in the use of iodized salt in Viet Nam since the National Iodine Deficiency Disorders Control Programme was suspended in 2005 has placed pregnant women and their infants in rural areas at risk of iodine deficiency disorders.

Childhood and adolescent predictors of leisure time physical activity during the transition from adolescence to adulthood: a population based cohort study

BACKGROUND

Few studies have investigated factors that influence physical activity behavior during the transition from adolescence to adulthood. This study explores the associations of sociodemographic, behavioral, sociocultural, attitudinal and physical factors measured in childhood and adolescence with physical activity behavior during the transition from adolescence to adulthood.

METHODS

Childhood and adolescent data (at ages 7-15 years) were collected as part of the 1985 Australian Health and Fitness Survey and subdivided into sociodemographics (socioeconomic status, parental education), behavioral (smoking, alcohol, sports diversity, outside school sports), sociocultural (active father, active mother, any older siblings, any younger siblings, language spoken at home), attitudinal (sports/recreational competency, self-rated health, enjoyment physical education/physical activity, not enjoying school sports) and physical (BMI, time taken to run 1.6 km, long jump) factors. Physical activity between the ages 15 and 29 years was reported retrospectively using the Historical Leisure Activity Questionnaire at follow-up in 2004-2006 by 2,048 participants in the Childhood Determinants of Adult Health Study (CDAH). Australia's physical activity recommendations for children and adults were used to categorize participants as persistently active, variably active or persistently inactive during the transition from adolescence to adulthood.

RESULTS

For females, perceived sports competency in childhood and adolescence was significantly associated with being persistently active (RR=1.88, 95% CI=1.39, 2.55). Smoking (RR=0.31 CI=0.12, 0.82) and having younger siblings (RR=0.69 CI=0.52, 0.93) were inversely associated with being persistently active after taking physical and attitudinal factors into account. For males, playing sport outside school (RR=1.47 CI=1.05, 2.08), having active fathers (RR=1.25 CI=1.01, 1.54) and not enjoying school sport (RR=4.07 CI=2.31, 7.17) were associated with being persistently active into adulthood. Time taken to complete the 1.6 km run was inversely associated with being persistently active into adulthood (RR=0.85 CI=0.78, 0.93) after adjusting for recreational competency.

CONCLUSIONS

Perceived sports competency (females) and cardiorespiratory fitness, playing sport outside school and having active fathers (males) in childhood and adolescence were positively associated with being persistently active during the transition from adolescence to adulthood.

The role of latitude, ultraviolet radiation exposure and vitamin D in childhood asthma and hayfever: an Australian multicenter study

Observations of increasing allergy prevalence with decreasing distance from the Equator and positive associations with ambient ultraviolet radiation have contributed to a growing interest in the possible role of vitamin D in the etiology of allergy. The aims of this study were to describe any latitudinal variation in the prevalence of childhood allergy in Australia and to evaluate, in parallel, the individual associations between ultraviolet radiation (UVR)- and vitamin D-related measures and hayfever asthma and both conditions. Participants were population-based controls who took part in a multicenter case-control study, aged 18-61 yr and resident in one of four study regions ranging in latitude from 27°S to 43°S. Data were derived from a self-administered questionnaire, interview and examination by a research officer and biologic sampling. Latitude and longitude coordinates were geocoded from participants' residential locations and climatic data were linked to postcodes of current residence. Stored serum was analyzed for 25-hydroxyvitamin D concentrations and silicone rubber casts of the skin were used as an objective measure of cumulative actinic damage. There was an inverse latitude gradient for asthma (a 9% decrease per increasing degree of latitude); however, this pattern did not persist after adjusting for average daily temperature. There was no association between any of the UVR- or vitamin D-related measures and childhood asthma, but greater time in the sun in winter between the ages 6-15 yr was associated with an increase in the odds of having hayfever [adjusted odds ratios (OR) 1.29; 95% CI 1.01-1.63]. Oral supplementation with cod liver oil in childhood increased the odds of a history of having both asthma and hayfever (2.87; 1.00-8.32). Further investigation of the possible role of early vitamin D supplementation in the development of allergy is warranted. Our results also suggest that solar exposure during childhood may be important in allergic sensitization. Plausible explanations, including biologic mechanisms, exist for both observations.

Association of change in daily step count over five years with insulin sensitivity and adiposity: population based cohort study

OBJECTIVES

To investigate the association between change in daily step count and both adiposity and insulin sensitivity and the extent to which the association between change in daily step count and insulin sensitivity may be mediated by adiposity.

DESIGN

Population based cohort study.

SETTING

Tasmania, Australia.

PARTICIPANTS

592 adults (men (n=267), mean age 51.4 (SD 12.2) years; women (n=325), mean age 50.3 (12.3) years) who participated in the Tasmanian component of the national AusDiab Study in 2000 and 2005.

MAIN OUTCOME MEASURES

Body mass index, waist to hip ratio, and HOMA insulin sensitivity at follow-up in 2005.

RESULTS

Over the five year period, the daily step count decreased for 65% (n=382) of participants. Having a higher daily step count in 2005 than in 2000 was independently associated with lower body mass index (0.08 (95% confidence interval 0.04 to 0.12) lower per 1000 steps), lower waist to hip ratio (0.15 (0.07 to 0.23) lower), and greater insulin sensitivity (1.38 (0.14 to 2.63) HOMA units higher) in 2005. The mean increase in HOMA units fell to 0.34 (-0.79 to 1.47) after adjustment for body mass index in 2005.

CONCLUSIONS

Among community dwelling, middle aged adults, a higher daily step count at five year follow-up than at baseline was associated with better insulin sensitivity. This effect seems to be largely mediated through lower adiposity.

Oral contraceptive use and bone mass in women aged 26-36 years

INTRODUCTION

The association between hormonal contraceptive use and bone mineral density remains controversial.

HYPOTHESIS

Hormonal contraceptive use is positively associated with bone mass in young premenopausal women.

METHODS

Cross-sectional analysis of data collected from women aged 26-36 years (n = 687) in the Childhood Determinants of Adult Health study-a longitudinal study investigating childhood determinants of cardiovascular disease, diabetes, and other chronic diseases in adulthood. Participants were not currently pregnant or breast-feeding. Contraceptive use was obtained by self-administered questionnaire. Women were categorized as combined oral contraceptive users (n = 219), progestogen-only contraceptive users (n = 43), and non-users of hormonal contraceptives (n = 425). Bone mass was measured by quantitative ultrasound.

RESULTS

Compared with women who were not using any hormonal contraceptives, women using combined oral contraceptives had significantly higher values of broadband ultrasound attenuation (BUA), speed of sound, and quantitative ultrasound index. These associations remained after adjustment for confounders. Progestogen-only contraceptive users had higher BUA than non-users, but the differences were not statistically significant in this small group.

CONCLUSION

Combined oral contraceptive use was associated with higher bone mass measured by quantitative ultrasound in this population-based sample of premenopausal women aged 26-36 while progestogen-only contraceptives appeared to have no deleterious effect on bone mass.

Menstrual irregularity and bone mass in premenopausal women: cross-sectional associations with testosterone and SHBG

Background

There have been few studies examining the associations between menstrual irregularity, androgens and bone mass in population-based samples of premenopausal women. This study aimed to describe the associations between menstrual pattern, testosterone, sex hormone binding globulin (SHBG) and bone mass in a population-based sample of premenopausal women.

Methods

Cross-sectional study (N = 382, mean age 31.5 years). Menstrual pattern was assessed by questionnaire, bone mass measured by quantitative ultrasound (QUS) and androgen status was assessed by levels of serum testosterone, SHBG and the free androgen index (FAI).

Results

Women with irregular cycles (n = 41, 11%) had higher free androgen index (FAI, P = 0.01) and higher QUS measurements including speed of sound (SOS, 1%, P < 0.05), quantitative ultrasound index (QUI, 7%, p < 0.05), and broadband ultrasound attenuation (BUA, 7%, p = 0.10). These associations persisted after adjustment for age and body mass index (BMI). After further adjustment for hormonal factors (either testosterone, SHBG or FAI), the strength of the associations was moderately attenuated, however, women with irregular cycles still had a 6% increase in mean QUS. Total testosterone, FAI and SHBG were also associated with QUS measures (testosterone and FAI, r +0.11 to +0.21, all p < 0.05; SHBG r -0.14 to -0.16, all p < 0.05) and the associations remained significant after adjustment.

Conclusion

Irregular menstrual cycles were associated with higher bone mass in this population-based sample of premenopausal women suggesting menstrual disturbance should continue to be evaluated but may be less harmful for bone mass. The association between menstrual irregularity and bone mass was partially mediated by markers of androgen status especially free testosterone.

Maternal antenatal peanut consumption and peanut and rye sensitization in the offspring at adolescence

BACKGROUND

There is considerable controversy whether maternal peanut ingestion during pregnancy might influence sensitization in later life. Objective To examine whether maternal peanut ingestion during pregnancy might increase sensitization in the offspring.

METHODS

A population-based longitudinal cohort study with 16 years follow-up was conducted (N=373). Subjects were recruited at birth as part of an infant health study. Maternal antenatal peanut consumption was documented at birth and peanut and rye sensitization were determined by measurement of serum-specific IgE at age 16.

RESULTS

Peanut sensitization was common (14%). In the entire cohort (n=310), there was no association between antenatal peanut ingestion and peanut sensitization (P=0.17). However, there was a strong association between antenatal peanut ingestion and decreased risk of rye sensitization and peanut sensitization in those (n=201) without a family history (FH) of asthma (Rye OR 0.30, 95% CI 0.14-0.63, P=0.001 and Peanut OR 0.18, 95% CI 0.04-0.78, P=0.02). There was an increased risk of rye sensitization in those (n=108) with a FH of asthma and antenatal peanut ingestion (Rye OR 2.69, 95% CI 1.11-6.51 P=0.03). It was considered that these sensitizations were likely to be related to the presence of IgE antibodies to cross-reacting carbohydrate epitopes common to rye and peanut allergens.

CONCLUSIONS AND CLINICAL RELEVANCE

Antenatal peanut ingestion may influence the development of IgE antibody to cross-reacting carbohydrate epitopes in later life. Genetic factors may modify this association.

Depression and insulin resistance: cross-sectional associations in young adults

OBJECTIVE

To examine the association between depressive disorder and insulin resistance in a sample of young adults using the Composite International Diagnostic Interview to ascertain depression status.

RESEARCH DESIGN AND METHODS

Cross-sectional data were collected from 1,732 participants aged between 26 and 36 years. Insulin resistance was derived from blood chemistry measures of fasting insulin and glucose using the homeostasis model assessment method. Those identified with mild, moderate, or severe depression were classified as having depressive disorder.

RESULTS

The 12-month prevalence of depressive disorder was 5.4% among men and 11.7% among women. In unadjusted models mean insulin resistance was 17.2% (95% CI 0.7-36.0%, P = 0.04) higher in men and 11.4% (1.5-22.0%, P = 0.02) higher in women with depressive disorder. After adjustment for behavioral and dietary factors, the increased level of insulin resistance associated with depressive disorder was 13.2% (-3.1 to 32.3%, P = 0.12) in men and 6.1% (-4.1 to 17.4%, P = 0.25) in women. Waist circumference was identified as a mediator in the relationship between depression and insulin resistance, reducing the beta coefficient in the fully adjusted models in men by 38% and in women by 42%.

CONCLUSIONS

A positive association was found between depressive disorder and insulin resistance in this population-based sample of young adult men and women. The association seemed to be mediated partially by waist circumference.

Combined effects of smoking, anti-EBNA antibodies, and HLA-DRB1*1501 on multiple sclerosis risk

OBJECTIVE

To examine the interplay between smoking, serum antibody titers to the Epstein-Barr virus nuclear antigens (anti-EBNA), and HLA-DR15 on multiple sclerosis (MS) risk.

METHODS

Individual and pooled analyses were conducted among 442 cases and 865 controls from 3 MS case-control studies-a nested case-control study in the Nurses' Health Study/Nurses' Health Study II, the Tasmanian MS Study, and a Swedish MS Study. Conditional logistic regression models were used to calculate odds ratios (ORs) and 95% CIs for the association between smoking, anti-EBNA titers, HLA-DR15, and MS risk. Study estimates were pooled using inverse variance weights to determine a combined effect and p value.

RESULTS

Among MS cases, anti-EBNA titers were significantly higher in ever smokers compared to never smokers. The increased risk of MS associated with high anti-EBNA Ab titers was stronger among ever smokers (OR = 3.9, 95% CI = 2.7-5.7) compared to never smokers (OR = 1.8, 95% CI = 1.4-2.3; p for interaction = 0.001). The increased risk of MS associated with a history of smoking was no longer evident after adjustment for anti-EBNA Ab titers. No modification or confounding by HLA-DR15 was observed. The increased risk of MS associated with ever smoking was only observed among those who had high anti-EBNA titers (OR = 1.7, 95% CI = 1.1-2.6).

CONCLUSIONS

Smoking appears to enhance the association between high anti-EBNA titer and increased multiple sclerosis (MS) risk. The association between HLA-DR15 and MS risk is independent of smoking. Further work is necessary to elucidate possible biologic mechanisms to explain this finding.