Homocysteine cognitive effect

The answer is A. The constellation of symptoms exhibited by this patient is characteristic of homocystinuria. The impairment of her cognitive function could be attributed to many conditions, but the key findings are ectopia lentis with downward lens dislocation and osteoporosis in a female of this age. Homocystinuria is produced by inherited deficiency of one of the enzymes in the pathway of Met conversion to Cys. The most common form is cystathionine P-synthase deficiency, which results in accumulation of all upstream components of the pathway, including homocysteine, which is responsible for the toxic effects, and Met, which becomes elevated in the blood. Cystathionine and cysteine, which are both downstream of the block in the pathway caused by cystathionine P Synthase deficiency, would be decreased. Metabolic pathways for lactate and urea are not involved in this disease mechanism. 

Miller AL. The methionine-homocysteine cycle and its effects on cognitive diseases. Altem Med... 

In the methionine cycle, cobalamin also plays a central role, as the methyl group of 5-methyltetrahydrofolate is first transferred to the cobalamin molecule and then further transferred to homocysteine to form methionine. This reaction explains the close connection of folate and cobalamin metabolism, as 5-methyltetrahydrofolate cannot be used for other reactions over than the methylation of homocysteine. Mild deficiency of folate and cobalamin is also associated with cognitive decline due to the neurotoxic effects of increased... 

Pyridoxine has been proposed a treatment for elevated levels of homocysteine, which is believed to be involved in the aetiology of coronary artery disease. There is some evidence that it promotes turnover of homocysteine. There is evidence that it can improve immtme function in the elderly when administered at levels about 2-3 x RDA. There is some evidence that pyridoxine supplementation may improve cognitive function in the elderly although not mood. There is some evidence that pyridoxine may reduce the risk of kidney stone formation. Pyridoxine has been used for many years in the treatment of morning sickness and there is some evidence that it is effective when used at levels of 25 mg every 8 hours. It has been used in treating premenstrual syndrome and there is some evidence that it is effective. It is recommended that pyridoxine supplementation is used with dmgs such as isoniazid and penicillamine that deplete its levels. Lar doses (0.1-1 g) have been used in the treatment of schizophrenia and it has been found that pyridoxine can interfere with the actions of LDOPA and phenytoin. 

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