This requires active folate and vitamin B12, in order to donate a methyl group. Active folate is known as 5-methyltetrahydrofolate (5-MTHF). Another pathway for the conversion of homocysteine back to methionine also exists, involving methylation with trimethylglycine (also called betaine or abbreviated to TMG) as a methyl donor. The remaining homocysteine is transsulfurated to cysteine, with vitamin B6 as the co-factor.Genetic defects in 5-MTHF reductase can consequently lead to hyperhomocysteinemia. The most common polymorphisms are known as MTHFR C677T and MTR A2756G. These polymorphisms occur in about 10% of the worlds population. Elevations of homocysteine can also occur in the rare hereditary disease homocystinuria. Diagnosis
A blood test can be performed to quantify total homocysteine concentration in the plasma, of which approximately 80% is generally protein-bound. Classification of hyperhomocysteinemia is defined with respect to serum concentration as follows:
Moderate: 15–30 nmol/mL (or μmol/L)
Intermediate: 30–100 nmol/mL
Severe: > 100 nmol/mLIf total homocysteine concentration is not found to be elevated, but clinical suspicion is still high, an oral methionine loading challenge several hours prior to quantification of homocysteine concentration may be used to increased sensitivity for marginal abnormalities of homocysteine metabolism.Fasting for 10 hours is sometimes recommended prior to measurement of homocysteine levels, but this may not be necessary for diagnostic yield. Treatment
Vitamins B6, B9, or B12 supplements (alone or combined), while they lower homocysteine level, do not change the risk of heart disease or prevent death in people who have heart disease when compared to standard care or to an inactive supplement in a clinical trial.
Painful bruising syndrome (also known as "autoerythrocyte sensitization", "Gardner–Diamond syndrome", and "psychogenic purpura") is an idiopathic trauma-induced condition seen in young to middle-aged women who sometimes manifest personality disorders. : 829   It is characterized by a distinctive localized purpuric reaction occurring primarily on the legs, face and trunk, with recurring painful ecchymoses variably accompanied by syncope, nausea, vomiting, gastrointestinal and intracranial bleeding.Patients with this condition can experience frequent painful bruising around joints and muscles. Because of the rarity of the disorder, there are few methods of support in place for patients.Many patients are labelled with the stigma of having a psychological condition without this having a specifically proven link. There have been cases of painful bruising syndrome reported where there are no additional psychological disorders. This has been known to be put into remission with chemotherapy. It was characterized in 1955 by Frank Gardner and Louis Diamond.Patient may present with a history of intermittent purpura mostly precipitated by stress. See also
List of cutaneous conditions

References
Further reading
Panconesi, E., & Hautmann, G. (1995). Stress, Stigmatization and Psychosomatic Purpuras. International Angiology 14: 130–137. Yuecel, B., Kiziltan, E., & Aktan, M. (2000). Dissociative Identity Disorder Presenting With Psychogenic Purpura. Psychosomatics 41: 279–281. == External links ==