[Remethylation disorders: about two cases].

In order to propose a course of action to be taken in the face of any hyperhomocysteinemia, we have reported for the first time in a French journal the recommendations made within the framework of the European E-HOD project for the diagnosis and treatment of remethylation disorders. The remethylation route ensures homocysteine-methionine conversion. It is linked to the folate cycle and the intracellular metabolism of cobalamins. Remethylation disorders can be classified into three groups: 1) isolated disorders (cblD-HC, cblE, cblG) corresponding to an isolated deficit in the production of methylcobalamin, cofactor of methionine synthase; 2) combined disorders (cblC, cblD-MMA/HC, cblF, cblJ) corresponding to an alteration of the transport and intracellular metabolism of cobalamins, which causes a defect in the synthesis of the two functional forms of cobalamin: methylcobalamin and adenosylcobalamin, a cofactor for methyl malonylCoA mutase; 3) MTHFR deficit, an abnormality of the folate cycle. The biological anomalies observed are hyperhomocysteinemia and hypomethioninaemia associated in the case of disorders combined with increased urinary excretion of methylmalonic acid. The clinical presentation is however heterogeneous according to the remethylation disorder but also for the same pathology according to the age. Given the large number of pathologies grouped together in remethylation disorders, this point is illustrated by only two clinical cases concerning the same deficit (deficit in MTHFR) but with different discovery circumstances: a neonatal form and a late form.