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Evidence exists linking elevated homocysteine levels with vascular dementia [10] and Alzheimer's disease. [11] [12] [13] There is also evidence that elevated homocysteine levels and low levels of vitamin B6 and B12 are risk factors for mild cognitive impairment and dementia. [14]
Total plasma homocysteine. Homocysteine levels typically are higher in men than women, and increase with age. [15] [16] Common levels in Western populations are 10 to 12 μmol/L, and levels of 20 μmol/L are found in populations with low B-vitamin intakes or in the elderly (e.g., Rotterdam, Framingham). [17] [18]
Vitamin B 12 deficiency, also known as cobalamin deficiency, is the medical condition in which the blood and tissue have a lower than normal level of vitamin B 12. [5] Symptoms can vary from none to severe. [1] Mild deficiency may have few or absent symptoms. [1]
Normal serum levels may be found in cases of deficiency where myeloproliferative disorders, liver disease, transcobalamin II, or small intestinal bacterial overgrowth are present. [ 56 ] [ 57 ] Low levels of serum vitamin B 12 may be caused by other factors than B 12 deficiency, such as folate deficiency , pregnancy , oral contraceptive use ...
Hence treatment includes both betaine and a diet low in methionine. In classical homocystinuria (CBS, or cystathione beta synthase deficiency), the plasma methionine level usually increases above the normal range of 30 micromoles/L and the concentrations should be monitored as potentially toxic levels (more than 400 micromoles/L) may be reached.
Vitamin B 12 was discovered as a result of pernicious anemia, an autoimmune disorder in which the blood has a lower than normal number of red blood cells, due to a deficiency of vitamin B 12. [5] [16] The ability to absorb the vitamin declines with age, especially in people over 60. [17]
Methylenetetrahydrofolate reductase deficiency is the most common genetic cause of elevated serum levels of homocysteine (hyperhomocysteinemia). It is caused by genetic defects in MTHFR, which is an important enzyme in the methyl cycle. [1] Common variants of MTHFR deficiency are asymptomatic and have only minor effects on disease risk. [2]
Increased homocysteine and methylmalonic acid in Vitamin B 12 deficiency; Increased homocysteine in folate deficiency; Normal levels of both methylmalonic acid and total homocysteine rule out clinically significant cobalamin deficiency with virtual certainty. [9]