Hyperhomocysteinemia – etiology, pathogenesis, and clinical manifestations.
Hyperhomocysteinemia is a condition characterized by elevated levels of homocysteine in the blood.
Homocysteine is a sulfur -containing amino acid produced during methionine metabolism.
Etiology
- 1 Genetic causes
- Cystathionine β-synthase (CBS) deficiency (classic homocystinuria; autosomal recessive).
- MTHFR (methylenetetrahydrofolate reductase) mutations, impairing remethylation of homocysteine to methionine.
- 2 Nutritional deficiencies
- Vitamin B12 deficiency.
- Folic acid deficiency.
- Vitamin B6 deficiency.
- These vitamins are essential cofactors in homocysteine metabolism.
- 3 Other causes
- Chronic renal failure (decreased homocysteine clearance).
- Hypothyroidism.
- Certain medications (e.g., methotrexate, anti- epileptics).
Pathogenesis
- Defective metabolism of homocysteine → accumulation in plasma.
- High homocysteine levels exert direct toxic effects on vascular endothelium:
- Promotes endothelial dysfunction.
- Increases oxidative stress.
- Stimulates smooth muscle proliferation.
- 3 Leads to enhanced atherogenesis and thrombosis:
- Increases LDL oxidation.
- Enhances platelet activation and clotting cascade.
Clinical manifestations
Cardiovascular
- Premature atherosclerosis → increased risk of:
- Coronary artery disease.
- Myocardial infarction.
- Stroke.
- Peripheral artery disease.
- Arterial and venous thromboses.
Skeletal and connective tissue (mainly in severe genetic forms)
- Marfanoid body habitus (tall, thin, long limbs).
- Osteoporosis.
- Joint hyperlaxity.
Ocular
- Ectopia lentis (lens dislocation), especially downward and inward (in homocystinuria).
Neurological
- Developmental delay, intellectual disability (in severe inherited forms).
- Psychiatric symptoms (depression, anxiety).
Skin and hair
- Fair complexion, malar flush (some cases).
Summary Table