Meta-analyses to investigate gene-environment interactions in neuroepidemiology.

BACKGROUND: Most chronic neurological diseases are caused by a combination of multiple genetic and environmental factors. Increasingly, gene-environment interactions (GxE) are being examined, providing opportunities to combine studies systematically using meta-analysis. METHODS: Systematic review of the literature on how to examine GxE using observational study designs, and how to conduct a meta-analysis of studies on GxE. RESULTS: Most methods and challenges related to a standard meta-analysis apply to a GxE meta-analysis. There are, however, some substantive differences. With GxE, there is the capability of using a case-only design. Research on GxE interactions may be more prone to publication bias, since interactions are usually not the primary hypothesis and only 'exciting' significant GxE findings are reported out of a range of secondary analyses. In disease aetiology research, there has been debate whether to measure interaction on a multiplicative or additive scale. There are some significant challenges associated with measuring interaction on an additive scale, and thus the uptake of the measures of additive interaction has been limited. As a result, the methods of analysing interaction have been less consistent and reporting has been highly variable. We suggest using the STROBE/STREGA reporting guidelines to allow evaluation of interaction on both scales. CONCLUSIONS: We identified a number of differences of a GxE meta-analysis over a standard meta-analysis. Awareness of these issues is important. Using established reporting guidelines for GxE studies is recommended. The development of consortia for neurological disorders that include both genetic and environmental data might offer benefits for GxE meta-analyses in the future.

Higher levels of reported sun exposure, and not vitamin D status, are associated with less depressive symptoms and fatigue in multiple sclerosis.

OBJECTIVE: Insufficient sun exposure and vitamin D deficiency have both been associated with increased risk of multiple sclerosis (MS). Depressi on, anxiety, fatigue and cognitive impairment are prevalent and disabling symptoms in MS. Our objective was to examine the associations between personal sun exposure and serum 25-hydroxyvitamin D (25(OH)D), and depression, anxiety, fatigue and cognition. METHODS: A total of 198 participants with multiple sclerosis were followed prospectively for an average of 2.3 years. Assessments of serum 25(OH)D, sun exposure, depression, anxiety and fatigue were carried out biannually; cognition was assessed annually. RESULTS: Personal reported sun exposure was inversely associated with depression scores (ß -0.26 (95%CI -0.40, -0.12);P ≤ 0.001) and fatigue scores (ß -0.65 (95%CI -1.23, -0.07); P = 0.028). Only high levels of 25(OH)D (>80 nm) were inversely associated depression scores (ß -0.64 (95%CI -1.15, -0.13); P = 0.015), but this was not significant after adjustment for reported sun exposure. No associations were seen between reported sun exposure or serum 25(OH)D levels and anxiety or cognition scores. CONCLUSION: We found that higher levels reported sun exposure, rather than 25(OH)D levels, were associated with less depressive symptoms and levels of fatigue. The role of UV or light therapy will need to be evaluated in randomized controlled trials to confirm an effect on these symptoms in MS.

The AusD Study: a population-based study of the determinants of serum 25-hydroxyvitamin D concentration across a broad latitude range.

Observational studies suggest that people with a high serum 25-hydroxyvitamin D (25(OH)D) concentration may have reduced risk of chronic diseases such as osteoporosis, multiple sclerosis, type 1 diabetes, cardiovascular disease, and some cancers. The AusD Study (A Quantitative Assessment of Solar UV Exposure for Vitamin D Synthesis in Australian Adults) was conducted to clarify the relationships between ultraviolet (UV) radiation exposure, dietary intake of vitamin D, and serum 25(OH)D concentration among Australian adults residing in Townsville (19.3°S), Brisbane (27.5°S), Canberra (35.3°S), and Hobart (42.8°S). Participants aged 18-75 years were recruited from the Australian Electoral Roll between 2009 and 2010. Measurements were made of height, weight, waist:hip ratio, skin, hair, and eye color, blood pressure, and grip strength. Participants completed a questionnaire on sun exposure and vitamin D intake, together with 10 days of personal UV dosimetry and an associated sun-exposure and physical-activity diary that was temporally linked to a blood test for measurement of 25(OH)D concentration. Ambient solar UV radiation was also monitored at all study sites. We collected comprehensive, high-quality data from 1,002 participants (459 males, 543 females) assessed simultaneously across a range of latitudes and through all seasons. Here we describe the scientific and methodological issues considered in designing the AusD Study.

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.

Vitamin D deficiency in Tasmania: a whole of life perspective.

AIM: This study aims to describe the lifetime picture of vitamin D deficiency, as measured by serum 25(OH)D concentration, in Tasmania (latitude 43°S). METHODS: Five cross-sectional studies were used: a sample of primary schoolchildren (n = 201, aged 7-8 years), two samples of adolescents (sample 1: n = 374, aged 15-18 years; sample 2: n = 136, aged 16-19 years), a sample of young to middle-aged adults (n = 262, aged 19-59 years) and a sample of older adults (n = 1092, aged 50-80 years). RESULTS: In winter/spring, approximately two-thirds of the adolescents and adults (young, middle-aged and older) had 25(OH)D levels ≤50 nmol/L, and around 10% had 25(OH)D levels ≤25 nmol/L. The prevalence of vitamin D deficiency was much lower for primary schoolchildren (11.5% < 50 nmol/L, 0.5% ≤ 25 nmol/L). In summer/autumn, approximately one-third of the adolescents and adults had 25(OH)D levels ≤50 nmol/L, and very few had 25(OH)D levels ≤25 nmol/L. For the adolescents and adults, even among those who reported the highest category of sun exposure, approximately 45% had 25(OH)D levels ≤50 nmol/L in winter/spring. CONCLUSIONS: Vitamin D deficiency was uncommon among our sample of primary school children but increased substantially during the teenage years and seemed to remain high throughout the rest of life, suggesting that mild vitamin D deficiency is endemic in Tasmania apart from in the very young.

Current and past Epstein-Barr virus infection in risk of initial CNS demyelination.

OBJECTIVES: To assess risk of a first clinical diagnosis of CNS demyelination (FCD) in relation to measures of Epstein-Barr virus (EBV) infection within the context of other known risk factors. METHODS: This was a multicenter incident case-control study. FCD cases (n = 282) aged 18-59 years and controls (n = 558, matched on age, sex, and region) were recruited from 4 Australian centers between November 1, 2003, and December 31, 2006. A nested study (n = 215 cases, n = 216 controls) included measurement of whole blood quantitative EBV DNA load and serum EBV-specific antibodies. Conditional logistic regression was used to analyze case-control differences. RESULTS: There were no significant case-control differences in the proportion with detectable EBV DNA (55.8% vs 50.5%, respectively, p = 0.28), or in quantitative EBV DNA load (p = 0.33). Consistent with previous work, higher anti-EBV-specific immunoglobulin G (IgG) titers and a history of infectious mononucleosis were associated with increased FCD risk and there was an additive interaction with HLA-DRB1*1501 status. We found additional interactions between high anti-EBNA IgG titer and SNPs in HLA-A (adjusted odds ratios [AOR] = 19.84 [95% confidence interval (CI) 5.95 to 66.21] for both factors compared to neither) and CTLA-4 genes (AOR = 0.31 [95% CI 0.13 to 0.76] for neither factor compared to both). EBV DNA load was lower at higher serum 25-hydroxyvitamin D concentrations in controls (r = -0.17, p = 0.01). An adverse effect of higher EBV DNA load on FCD risk was increased with higher 25-hydroxyvitamin D concentration (p[interaction] = 0.02). CONCLUSION: Past infection with EBV, but not current EBV DNA load in whole blood, is significantly associated with increased FCD risk. These associations appear to be modified by immune-related gene variants.

Individual and joint action of environmental factors and risk of MS.

In this review, the evidence for the leading environmental and lifestyle factors thought to play a role in multiple sclerosis (MS) onset, including Epstein-Barr virus, sun exposure or vitamin D, and smoking, will be discussed. The Causal Pie Model is used as a conceptual framework to understand the causation. Given that no single factor leads to the development of MS, the joint action or interaction of these factors, along with genetic factors, most particularly the HLA-DR15*1501 genotype, is a primary focus.

Heterogeneity at the HLA-DRB1 allelic variation locus does not influence multiple sclerosis disease severity, brain atrophy or cognition.

BACKGROUND: HLA-DRB1*1501 (DR15) and other HLA class II alleles increase the risk of developing multiple sclerosis (MS). However, the contribution of genetic heterogeneity to the clinical course of MS remains controversial. We examined the influence of DR15 and other common DRB1 alleles (DRB1*01 (DR1), DRB1*03 (DR3) and DRB1*04 (DR4) on MS severity in a large, Australian, population-based cohort. METHODS: We studied the association between common HLA-DRB1 alleles and genotypes and age of onset as well as three clinical disease severity descriptors: Multiple Sclerosis Severity Score, progression index), and the interval between the first and second attack in 978 patients with relapsing remitting MS and secondary progressive MS. We assessed cognition using the Symbol Digit Modalities Test in 811 patients and brain atrophy using the linear magnetic resonance imaging marker, the intercaudate ratio, in 745 patients. RESULTS: Carrying DR15 significantly decreased the age of MS onset by 3.2 years in homozygotes and 1.3 years in heterozygotes. Carrying the HLA-DR15, -DR1, -DR3 or -DR4 alone or in combination did not affect clinical disease severity, cognition or cerebral atrophy. CONCLUSIONS: This study confirms that heterogeneity of HLA-DRB1 does not influence disease outcome in relapsing MS patients, with the exception of a younger age of onset in HLA-DR15 carriers.

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.

Apolipoprotein genotype does not influence MS severity, cognition, or brain atrophy.

BACKGROUND: The influence of APOE allelic heterogeneity on multiple sclerosis (MS) disease severity has been reported in multiple datasets with conflicting results. Several studies have reported an unfavorable association of APOE epsilon4 with more severe clinical disease course while, in contrast, APOE epsilon2 has been associated with a more benign disease course. In this study, we examine the influence of heterogeneity of the APOE gene on disease severity in a large, Australian, population-based MS cohort. METHODS: Associations between APOE allele status, 2 promoter region single nucleotide polymorphisms (-219 G/T and +113 C/G), and 4 measures of disease severity were tested in 1,006 patients with relapsing-remitting MS and secondary progressive MS: 1) Multiple Sclerosis Severity Score; 2) Progression Index (Expanded Disability Status Scale/disease duration); 3) age at first symptom; and 4) interval between the first and second attack. The Symbol Digit Modalities Test was used as a single cognitive marker in 889 patients. Brain atrophy was measured in 792 patients using the intercaudate ratio. APOE epsilon4 and epsilon3 carriers were stratified by -219 G/T or +113 C/G to investigate haplotypic heterogeneity in the APOE gene region. RESULTS: In this MS study, neither APOE allele status nor promoter region heterogeneity at positions -219 G/T or +113 C/G influenced the clinical disease severity, cognition, or cerebral atrophy. CONCLUSIONS: Allelic and haplotypic heterogeneity of the APOE gene region does not influence multiple sclerosis disease course in this well-defined Australian multiple sclerosis cohort.

Validation of linear cerebral atrophy markers in multiple sclerosis.

Linear measures of cerebral ventricular enlargement may act as surrogate measures of cerebral atrophy in multiple sclerosis (MS). Linear atrophy markers were measured from routine MRI scans during a population survey of 171 Tasmanian MS patients and 91 healthy controls. Thirty-five Victorian MS clinic patients were recruited as a validation cohort with 14 of these re-assessed 4 years later. In the population survey, we measured three linear brain atrophy markers: inter-caudate distance (ICD), third ventricle width (TVW) and frontal horn width (FHW). TVW (OR 2.0, p=0.001) and ICD (OR 16.1, p<0.001) differentiated between MS cases and controls. In the validation study, we correlated the intercaudate ratio (ICR=ICD/brain width) and third ventricular ratio (TVR=TVW/brain width) with brain parenchymal volume. Cross-sectionally, ICR (R=-0.453, p<0.01) and TVR (R=-0.653, p<0.01) were correlated with brain parenchymal volume. Longitudinally, brain parenchymal volume loss was inversely correlated with increased ICD (R=-0.77, p<0.01) and TVW (R=-0.71, p<0.01). This study shows that ICD measurements obtained from clinical MRI scans are valid brain atrophy measures for use in monitoring MS progression.

Vitamin D levels in people with multiple sclerosis and community controls in Tasmania, Australia.

BACKGROUND: Adequate 25(OH)D levels are required to prevent adverse effects on bone health. Population-based data on factors associated with 25(OH)D levels of people with MS have been lacking. OBJECTIVES: To examine the prevalence and determinants of vitamin D insufficiency in a population-based sample of MS cases and controls, and to compare 25(OH)D status between MS cases and controls, taking into account case disability. METHODS: We conducted a population based case-control study in Tasmania, Australia (latitude 41-43 degrees S) on 136 prevalent cases with MS confirmed by magnetic resonance imaging and 272 community controls, matched on sex and year of birth. Measurements included serum 25(OH)D, sun exposure, skin type, dietary vitamin D intake and disability including EDSS. RESULTS: A high prevalence of vitamin D insufficiency was found in MS cases and controls. Among MS cases, increasing disability was strongly associated with lower levels of 25(OH)D and with reduced sun exposure. Cases with higher disability (EDSS > 3) were more likely to have vitamin D insufficiency than controls (OR = 3.07 (1.37, 6.90) for 25(OH)D

Validity and reliability of adult recall of past sun exposure in a case-control study of multiple sclerosis.

BACKGROUND: Measurement of past sun exposure through recall by adults has the potential for measurement error. We aimed to investigate aspects of validity and reliability of self-reported past sun exposure. METHODS: A population-based case-control study was conducted in Tasmania on 136 cases with multiple sclerosis and 272 age- and sex-matched community controls. Repeat interviews on 52 cases and 52 controls were done on average 11 weeks after the initial interview. Sun exposure was assessed by questionnaire and lifetime calendar. Other measurements included serum 25-hydroxyvitamin D, actinic damage, and skin phenotype. RESULTS: There was an association between recent sun exposure and serum vitamin D (time in the sun: r = 0.22, P < 0.01; activities outside: r = 0.31, P < 0.01 for controls) and between lifetime sun exposure and actinic damage [correlation between 0.34 (P < 0.01) and 0.17 (P = 0.01) for controls]. The test-retest weighted kappa statistic of self-reported sun exposure ranged from 0.43 to 0.74. Recall of childhood/adolescent sun exposure by standardized questioning was no less reproducible than recall of recent adult sun exposure and no less reliable when made with the calendar method. Comparing the questionnaire and calendar method, the measures of childhood/adolescent sun exposure had a similar predictive validity for multiple sclerosis. CONCLUSIONS: The results of this study provide further evidence that adults are able to recall past sun exposure with shown validity and reliability and present information about the possible reasons for the good reliability of recalled sun exposure measures.

UVR, vitamin D and three autoimmune diseases--multiple sclerosis, type 1 diabetes, rheumatoid arthritis.

We review the evidence indicating a possible beneficial role for UVR on three Th1-mediated autoimmune diseases: multiple sclerosis, type 1 diabetes and rheumatoid arthritis in relation to recent developments in photoimmunology. Recent work suggests that UVR exposure may be one factor that can attenuate the autoimmune activity leading to these three diseases through several pathways involving UVB and UVA irradiation, UVR-derived vitamin D synthesis and other routes such as alpha-melanocyte-stimulating hormone, calcitonin gene related peptide and melatonin. Ecological features, particularly a gradient of increasing prevalence of multiple sclerosis and type 1 diabetes with higher latitude, provide some support for a beneficial role of UVR. Analytical studies provide additional support, particularly as low vitamin D has been prospectively associated with disease onset for all three diseases, but are not definitive. Randomized controlled trial data are required. Further, we discuss how associated genetic studies may assist the accumulation of evidence with regard to the possible causal role of low UVR exposure and/or low vitamin D status in the development of these diseases.

Past exposure to sun, skin phenotype, and risk of multiple sclerosis: case-control study.

OBJECTIVE: To examine whether past high sun exposure is associated with a reduced risk of multiple sclerosis. DESIGN: Population based case-control study. SETTING: Tasmania, latitudes 41-3 degrees S. PARTICIPANTS: 136 cases with multiple sclerosis and 272 controls randomly drawn from the community and matched on sex and year of birth. MAIN OUTCOME MEASURE: Multiple sclerosis defined by both clinical and magnetic resonance imaging criteria. RESULTS: Higher sun exposure when aged 6-15 years (average 2-3 hours or more a day in summer during weekends and holidays) was associated with a decreased risk of multiple sclerosis (adjusted odds ratio 0.31, 95% confidence interval 0.16 to 0.59). Higher exposure in winter seemed more important than higher exposure in summer. Greater actinic damage was also independently associated with a decreased risk of multiple sclerosis (0.32, 0.11 to 0.88 for grades 4-6 disease). A dose-response relation was observed between multiple sclerosis and decreasing sun exposure when aged 6-15 years and with actinic damage. CONCLUSION: Higher sun exposure during childhood and early adolescence is associated with a reduced risk of multiple sclerosis. Insufficient ultraviolet radiation may therefore influence the development of multiple sclerosis.