Inherited homocystinurias, have in common, accumulation of homocysteine with subsequent neurotoxicity; they also encompass two distinctive clinical entities: classical homocystinuria due to cystathionine β-synthase (CBS) deficiency and the rare inborn errors of cobalamin and folate metabolism. In the latter group, remethylation disorders of homocysteine to methionine (chiefly CblC defect and 5,10-methylenetetrahydrofolate reductase [MTHFR] deficiency) are by far the most frequently encountered situations. The natural history of CBS deficiency is relatively well known and described. Similarly, clinical presentations of remethylation defects are becoming better recognized and reported. Conversely, few data are available regarding treatment of these disorders, especially for remethylation defects. In this review, after an overview of the metabolic pathophysiology and the clinical features of inherited homocystinurias due to CBS deficiency, CblC defect, and MTHFR deficiency, we focus on present and prospective therapeutic approaches.
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