Madeleine K. M. Adams

Abdominal Obesity and Age-related Macular Degeneration

Evidence for an association between age-related macular degeneration (AMD) and obesity is inconsistent. The authors examined associations between adiposity and AMD prevalence using 21,287 participants from the Melbourne Collaborative Cohort Study aged 40-69 years at baseline (1990-1994). For men, each increase of 0.1 in waist/hip ratio (~1 standard deviation) was associated with a 13% increase in the odds of early AMD (odds ratio = 1.13, 95% confidence interval: 1.01, 1.26; P = 0.03) and a 75% increase in the odds of late AMD (odds ratio = 1.75, 95% confidence interval: 1.11, 2.76; P = 0.02). No other adiposity measure was associated with early AMD for men. Smoking status modified the relation between waist/hip ratio and early AMD (P = 0.05), with no association for former smokers. For women, there were inverse associations with early AMD for all adiposity measures (odds ratios = 0.89-0.93; P = 0.002-0.02), but no associations were observed for late AMD. This study confirms abdominal obesity as an AMD risk factor for men despite a survivorship effect from competing risks in morbidity and mortality. The inverse associations for women may reflect weaker true positive associations with AMD that are insufficient to overcome the survivorship effect. New data are provided on complex interactions between environmental exposures and AMD risk.

The prevalence and risk factors of epiretinal membranes: the Melbourne Collaborative Cohort Study.

Purpose: To determine the prevalence of epiretinal membranes (ERMs) in Melbourne, Australia and its risk factors in this population. Methods: The Melbourne Collaborative Cohort Study is a prospective study investigating the role of diet and life style in the causation of common chronic diseases. Eighty-six percent of participants were of Northern European origin born in Australia or United Kingdom and 14% were migrants from Greece or Italy (Southern European origin). Nonmydriatic digital retinal photography was implemented at Melbourne Collaborative Cohort Study follow-up. The ERMs were recorded as cellophane macular reflex without retinal folds or preretinal macular fibrosis (PMF) with retinal folds. Results: A total of 22,406 participants had retinal photography, 95% (n = 21,241) were eligible for ERM grading. The ERM prevalence were 8.9% (1,882); cellophane macular reflex, 4.9% (1,047); and preretinal macular fibrosis, 3.9% (835). After adjustment for age, sex, level of education, smoking status, level of cholesterol, body mass index, waist-to-hip ratio, waist measurement, blood pressure, diabetes, and stroke, increasing age and Southern European ethnicity was significantly associated with ERMs. Overall, in Southern Europeans, ERMs odd ratio was 1.97 (95% confidence intervals, 1.67–2.31), P < 0.001; preretinal macular fibrosis was 1.82 (95% confidence intervals, 1.43–2.31), P < 0.001; and cellophane macular reflex was 1.93 (1.57–2.38), P < 0.001. Conclusion: In an older Australian population, the prevalence of ERMs was 8.9% and was almost two times higher in participants of Southern European origin than Northern European origin.

Apolipoprotein E Gene Associations in Age-related Macular Degeneration The Melbourne Collaborative Cohort Study

The apolipoprotein E gene (APOE) has been found to be associated with age-related macular degeneration (AMD). Reported associations have been questioned, as they are opposite those for Alzheimers disease and cardiovascular disease. The authors examined associations between APOE genotype and AMD using a case-control study (2,287 cases and 2,287 controls individually matched on age, sex, and country of origin) nested within Melbourne Collaborative Cohort Study participants aged 48-86 years at AMD detection. The odds ratio for early AMD among participants with ε2-containing genotypes (ε2ε2/ε2ε3/ε2ε4) was 1.32 (95% confidence interval (CI): 1.11, 1.58; P = 0.002) versus persons with genotype ε3ε3. Associations with early AMD varied by smoking status; ε2-containing genotypes were positively associated with early AMD for never and previous smokers (never smokers: odds ratio (OR) = 1.40, 95% CI: 1.12, 1.76 (P = 0.003); previous smokers: OR = 1.39, 95% CI: 1.00, 1.93 (P = 0.05)) but not for current smokers (OR = 0.66, 95% CI: 0.34, 1.30 (P = 0.2; interaction P = 0.05). The ε4-containing genotype group (ε3ε4/ε4ε4) had an inverse association with early AMD among current smokers only (OR = 0.41, 95% CI: 0.22, 0.77 (P = 0.005)). These results highlight the importance of stratifying by smoking status in elderly populations. Smokers who survive to old age may be more likely to possess unknown genotypes which modify exposure-disease associations.

Can genetic associations change with age? CFH and age-related macular degeneration

Genetic variation in the gene encoding complement factor H (CFH) on chromosome 1q31 has repeatedly been associated with an increased risk of age-related macular degeneration (AMD); however, previous studies have had inadequate numbers of participants across a sufficiently wide age range to determine whether the association varies by age. We conducted a genetic case-control study using data from 2294 cases and 2294 controls selected from the Melbourne Collaborative Cohort Study, matched on age, sex and region of origin. Four consistently replicated CFH single-nucleotide polymorphisms (SNPs) were genotyped: rs1061170 (Y402H), rs2274700, rs393955 and rs800292; their relationship with AMD prevalence was determined across the age range 48-86. A difference in genotype frequencies was seen across age groups, where the low-risk homozygote prevalence rose with each increasing age group. Associations with early AMD were strongly modified by age for three of the four SNPs (interaction P-value: 0.01-0.00003). An inverse association between the high-risk homozygote for each SNP and early AMD was observed in the younger age groups [odds ratios (OR) range 0.37-0.48 for age <55], reversing to a positive association with increasing age (OR 1.87-2.8 for age >75). The direction of associations for this gene change was from inverse to risk with increasing age. These findings have important implications for predictive models for AMD and potentially other age-related diseases which extrapolate risks from older cohorts, as they assume homogeneity of association by age, which might not exist.

Age-Related Macular Degeneration in Ethnically Diverse Australia: Melbourne Collaborative Cohort Study

Abstract Purpose: To determine and compare the prevalence of age-related macular degeneration (AMD) in older Australians of Anglo-Celtic and Southern European origin. Methods: A total of 21,132 participants of the Melbourne Collaborative Cohort Study, aged 47–86 years, were assessed for AMD in 2003–2007 with non-mydriatic fundus photography. Of these, 14% were born in Southern Europe (Greece, Italy or Malta), with the remaining 86% of Anglo-Celtic origin, born in Australia, the United Kingdom or New Zealand. Results: Overall, 2694 participants (12.7%) had early stages of AMD, defined as either one or more drusen ≥125 μm (with or without pigmentary abnormalities) or one or more drusen 63–124 μm with pigmentary abnormalities in a 6000-μm diameter grading grid, in the absence of late AMD in either eye. A total of 122 participants (0.6%) had late AMD, defined as either geographic atrophy or neovascular AMD. In logistic regression analysis, adjusted for age, sex, smoking, education and physical activity, Southern Europeans compared to Anglo-Celts had a higher prevalence of the early stages of AMD (odds ratio, OR, 1.15, 95% confidence interval, CI, 1.00–1.34), and lower prevalence of late AMD (OR 0.36, 95% CI 0.17–0.78). Conclusions: Australians of Southern European origin have a higher prevalence of the early stages of AMD and lower prevalence of late AMD compared to those of Anglo-Celtic origin. Although AMD prevalence in the older age group(s) of Southern Europeans could be underestimated due to disparity in participation rates, it is likely that both lifestyle and genetic factors play their parts in differential AMD prevalence in these ethnic groups.

Twin study implicates genetic factors in dry eye disease.

Dry eye is a common chronic ocular condition that significantly reduces the quality of life of afflicted individuals. As well as a frequent cause of ocular irritation, dry eye can lead to visual disability, and may compromise the results of corneal, cataract, and refractive surgery. The average cost to US society of managing dry eye has been estimated at

20/20—Alcohol and Age-related Macular Degeneration The Melbourne Collaborative Cohort Study

55.4 billion. Dry eye disease encompasses a group of disorders of the tear film; attributed to either reduced tear production or excessive tear evaporation, or both. There may be inconsistent correlation between symptoms and signs, making clinical diagnosis problematic. Current treatments are largely palliative. Although symptoms can improve with treatment, there is no cure. Epidemiologic information on dry eye disease has been limited by the variety of definitions employed and the lack of diagnostic tests of high sensitivity and specificity. Female sex, increasing age, Sjorgren’s syndrome, and smoking have been identified as risk factors; other systemic diseases are also associated. Understanding the genetic factors of a disease can provide insights into the pathogenesis of disease, and hence lead to more effective treatment. To date, there is very little information on the role genetics plays in the dry eye phenotype, or the relative importance they have to environmental factors. Vehof et al. have employed an elegant classical twin study using a cohort of British, middle aged, elderly female twins. Despite the difficulties in phenotyping this multifactorial disease, they have demonstrated that genes are moderately important in dry eye disease. A heritability of approximately 30% was indicated for symptoms and 40% for diagnosis, with a varying heritability of 25% to 80% for various selected signs; the unique environment explained the remainder of the variance. Vehof et al. have paved the way for further genetic studies by showing that genetic factors play a significant role in dry eye disease.