A genetic predisposition to high homocysteine (hyper homocysteinemia) causes inability to metabolize the amino acid homocysteine, resulting in vascular constriction that drives up blood pressure, peripheral vascular disease, peripheral neuropathies, and ocular nerve damage with restricted circulation—meaning some cases of hypertension are caused not by heart dysfunction but by elevated homocysteine and can be treated by supplementing for the methylation deficiency that prevents homocysteine metabolism.