A 21-year-old man with premature arteriosclerosis and mental retardation is found to have homocystinuria. The following is/are true:

c. Arteriosclerotic plaques in this condition are atypically void of lipid deposition

d. Homocysteine exists in plasma in three forms: protein bound, mixed and free

Homocystinuria reflects homocystinemia which is associated with ectopia lentis, mental retardation and thromboembolic disorders as well as arteriosclerosis. There are three enzyme deficiencies known to cause the disorder as well as deficiencies of the cofactors pyridoxine, cobalamin and folate. Lipid deposition in plaques is characteristically absent. Homocysteine exists in plasma as the mixed disulfide homocysteine cysteine, as free and as protein bound homocysteine.