However, the science is strongly supporting the biochemistry that homocysteine degrades and inhibits the formation of the three main structural components of the artery, collagen, elastin and the proteoglycans. Homocysteine permanently degrades cysteine disulfide bridges and lysine amino acid residues in proteins, gradually affecting function and structure. Simply put, homocysteine is a 'corrosive' of long-living proteins, i.e. collagen or elastin, or life-long proteins, i.e. fibrillin.
http://en.wikipedia.org/wiki/Homocysteine
Among the factors that promote genetic instability and carcinogenesis, the impairment of homocysteine/folate (one-carbon metabolism) is considered to be an important risk factor associated with an unbalanced diet or genetic defects. A growing body of evidence suggests that the disturbance of this metabolism is also involved in neuronal abnormalities. The disturbance of one-carbon metabolism is thought to cause a chronic DNA precursor imbalance by blocking synthesis of purines and thymidine.
http://www.jbc.org/content/279/42/43952.full