Age, family history primary factors in development of AMD

Fort Lauderdale, FL-Numerous factors have been studied to determine an association with the development of age-related macular degeneration (AMD), according to Barbara Klein, MD, MPH. Family history, however, is by far the factor that stands out among the crowded arena of suspects. She reported why this is the case at the annual meeting of the Association for Research in Vision and Ophthalmology.

When the AMD epidemiology literature is reviewed, three common risk factors crop up for the disease: age, family history, and smoking. Numerous potential risks factors have been considered as causes of AMD, including: atherosclerosis, serum lipids, pulmonary disease, blood pressure, gout, arthritis, body mass index, inflammatory factors, alcohol intake, caffeine, physical activity level, hormone replacement therapy, diet and dietary supplements, light exposure, iris color, presence of cataract, refraction, and some sociodemographic factors. With most, the findings among studies were inconsistent.

One of the most consistent findings has been the impact of smoking, which has been found to be related to early and late AMD lesions in many but not all studies. The prevalence and incidence findings are not consistent, said Dr. Klein, professor, department of ophthalmology, University of Wisconsin, Madison.

Three studies have been published and another is about to be published concerning a polymorphism encoding complement factor H in region 1q25-31 that appears to be associated with AMD in some families, she said. Also, a variant in the toll-like receptor region at 9q32 appears to be associated with increased risk of AMD, but another variant is not, she continued.

Dr. Klein and her colleagues looked at the genetics of AMD in a study of affected families. In the Family Age-Related Macular Degeneration Study (FARMS), which included 32 affected families that were highly ascertained, the investigators found that only three families had a link to the peak on 1q. In the Beaver Dam Eye Study, in which 602 families (2,300 people) that were not ascertained participated, analysis of the CIH locus is pending, however linkage to markers in regions 1p35 and 15q22 has been found. The FARMS families also have a peak on chromosome 15, Dr. Klein explained.

Genetic, environmental factors

"The influence of any particular gene may depend on the effects of other genes and environmental factors. An approach that embraces personal and environmental factors and modifier genes influencing disease expression is likely to be the most informative way to find out more about macular degeneration," she said.

Factors that still need to be considered, she advised, as the research into AMD continues, are understanding the ascertainment methods and biases for the patients involved in the various studies of AMD; if there are genotypic and phenotypic heterogeneity problems that have an impact on the study results; why common variants in genes are associated with disease only in some patients; why early AMD lesions progress to late lesions in some patients only; and what other risk factors-either genetic or environmental-affect risk or change the expression.