Yongwoo Kim MD (

Dr. Kim of Temple University Lewis Katz School of Medicine has no relevant financial relationships to disclose.

Steven R Levine MD, editor. (

Dr. Levine of the SUNY Health Science Center at Brooklyn has no relevant financial relationships to disclose.

Originally released April 13, 1998; last updated November 28, 2018; expires November 28, 2021

This article includes discussion of hyperhomocysteinemia, hyperhomocystinemia, homocysteinemia, homocysteinuria, hereditary homocystinuria, and homocysteine elevation. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.


In this article, the author discusses hyperhomocysteinemia and reviews developments in the understanding of its relationship with cerebrovascular disease and dementia. Although folic acid, vitamin B12, and vitamin B6 lower homocysteine levels, many recent randomized, controlled trials suggest that treatment with these vitamins does not clearly lower the risk of vascular disease.

Key points


Severe hyperhomocysteinemia (homocysteine level >100 µM, also called as homocysteinuria) is associated with congenital manifestation of ectopia lentis, myopia, marfanoid features, livedo reticularis, malar rash, intellectual disability, seizure, and also with arterial and venous vascular thromboembolism.


Moderate hyperhomocysteinemia (homocysteine level 15 µM - 100 µM) is associated with increased risk of cerebrovascular disease and cognitive dysfunction.


• Vitamin B complex (folic acid, pyridoxine, cobalamin) can lower homocysteine levels and has been a main treatment for severe hyperhomocysteinemia.


• In moderate hyperhomocysteinemia, the effectiveness of vitamin B complex therapy in order to prevent stroke or dementia is not well established.

Historical note and terminology

Hyperhomocysteinemia is defined as elevation of plasma total concentration of homocysteine and disulfide adducts of homocysteine collectively termed "homocyst(e)ine" or "total homocysteine."

The hypothesis that hyperhomocysteinemia is a risk factor for vascular disease was proposed in 1969 by McCully, who observed advanced arteriosclerosis in children with rare inherited disorders causing markedly elevated levels of total plasma homocysteine (McCully 1969). There has been a resurgence of interest in hyperhomocysteinemia because of the recognition that even moderately elevated concentrations of total plasma homocysteine are associated with increased risk of stroke, cardiovascular disease, and venous thrombosis (den Heijer et al 1998; Sacco et al 1998; Eikelboom et al 1999).

Categorizing homocysteine levels into severe, moderate, and normal ranges is useful. Severe hyperhomocysteinemia is defined as a fasting total plasma homocysteine concentration greater than 100 µM. Moderate hyperhomocysteinemia is defined as a fasting total plasma homocysteine concentration between 15 µM and 100 µM. Mean fasting concentrations of total plasma homocysteine are usually less than or equal to 10 µM, with the 95th percentile at approximately 15 µM.

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