Homocysteine was first described by Butz and du Vigneaud in 1932. However a link to human disease was not suggested until 1962. Carson and Neil discovered high homocysteine concentrations in the urine of some children with mental retardation. The elevated homocysteine levels in these patients were caused by enzyme defects which blocked the metabolism of homocysteine (see The Biochemistry of Homocysteine).
This condition is known as homocystinuria, and was later found to be associated with premature cardiovascular disease. The symptoms also affect childhood, resulting in approximately 25% of these patients dying before the age of 30 from cardiovascular events.
During the last 15 years it has been thoroughly documented that even moderately elevated homocysteine levels are a strong risk factor for cardiovascular disease (disease of the heart and blood vessels). Many studies have also found an association between high homocysteine, impaired cognitive performance and dementia development and progression.
Further information on the harmful effects of homocysteine can be found here.