MSH: Condition in which the plasma levels of homocysteine and related metabolites are elevated (>13.9 Î¼mol/l). Hyperhomocysteinemia can be familial or acquired. Development of the acquired hyperhomocysteinemia is mostly associated with vitamins B and/or folate deficiency (e.g., PERNICIOUS ANEMIA, vitamin malabsorption). Familial hyperhomocysteinemia often results in a more severe elevation of total homocysteine and excretion into the urine, resulting in HOMOCYSTINURIA. Hyperhomocysteinemia is a risk factor for cardiovascular and neurodegenerative diseases, osteoporotic fractures and complications during pregnancy.,NCI: A serious metabolic condition caused by mutations in the MTHFR gene, medications, or nutritional deficiency. It results in increased levels of homocysteine in the blood. Patients with this condition are at an increased risk for recurrent blood clots formation and cardiovascular accidents.