Elevated homocysteine levels may be a biomarker for increased risk of AMD

People who have elevated homocysteine in their blood, an amino acid that is a known biomarker for cardiovascular disease, may also be at an increased risk of developing age-related macular degeneration (AMD), according to a study in the January issue of the American Journal of Ophthalmology.

This research was conducted at the Massachusetts Eye and Ear Infirmary and Devers Eye Institute in Portland, Ore.

In this largest study of the relationship of this amino acid and AMD, researchers measured the fasting plasma homocystein levels of 934 individuals who were participating in an ancillary study of the Age-Related Eye Disease Study. Five hundred and forty seven people with AMD and 387 control subjects were tested.

"We found that elevated homocysteine in the blood may be another biomarker for increased risk of AMD," said lead author Johanna M. Seddon, MD, director of epidemiology at the Massachusetts Eye and Ear Infirmary. Seddon is also an associate professor of ophthalmology at Harvard Medical School. "Homocysteine can be reduced by dietary intake of vitamins B6, B12, and folate, so the relationship between this amino acid and AMD deserves further study."

Researchers found that median values were higher among people with advanced stages of AMD compared to people without AMD, controlling for age and other factors. Levels considered high in the clinical setting (above 12 mmol/l) were also associated with a higher risk of AMD. Seddon's finding adds to the growing body of evidence that there may be overlapping disease mechanisms between AMD and cardiovascular diseases.

Age-related macular degeneration is the leading cause of irreversible visual impairment and blindness among persons aged 60 and older. With the elderly population steadily growing, the burden related to this loss of visual function will increase. Limited treatment options exist and prevention remains the best approach for addressing this public health concern.

Seddon and colleagues first proposed this potential relationship between homocysteine and AMD in the mid-1990s and published this hypothesis in a review article in 1999. She and her team previously established that smoking and nutrition are modifiable factors associated with the development and progression of AMD. They are now also searching for the genes involved in the etiology of this increasing cause of blindness.