Clinical and molecular characterization of adult patients with late-onset MTHFR deficiency.

5,10-Methylenetetrahydrofolate reductase (MTHFR) deficiency usually presents as a severe neonatal disease. This study aimed to characterize natural history, biological and molecular data, and response to treatment of patients with late-onset MTHFR deficiency. The patients were identified through the European Network and Registry for Homocystinuria and Methylation Defects and the Adult group of the French Society for Inherited Metabolic Diseases; data were retrospectively colleted. To identify juvenile to adult-onset forms of the disease, we included patients with a diagnosis established after the age of 10 years. We included 14 patients (median age at diagnosis: 32 years; range: 11-54). At onset (median age: 20 years; range 9-38), they presented with walking difficulties (n = 8), cognitive decline (n = 3) and/or seizures (n = 3), sometimes associated with mild mental retardation (n = 6). During the disease course, symptoms were almost exclusively neurological with cognitive dysfunction (93%), gait disorders (86%), epilepsy (71%), psychiatric symptoms (57%), polyneuropathy (43%), and visual deficit (43%). Mean diagnostic delay was 14 years. Vascular events were observed in 28% and obesity in 36% of the patients. One patient remained asymptomatic at the age of 55 years. Upon treatment, median total homocysteine decreased (from 183 µmol/L, range 69-266, to 90 µmol/L, range 20-142) and symptoms improved (n = 9) or stabilized (n = 4). Missense pathogenic variants in the C-terminal regulatory domain of the protein were over-represented compared to early-onset cases. Residual MTHFR enzymatic activity in skin fibroblasts (n = 4) was rather high (17%-58%). This series of patients with late-onset MTHFR deficiency underlines the still unmet need of a prompt diagnosis of this treatable disease.

[Remethylation disorders: about two cases]. / Troubles de la reméthylation : à propos de deux cas.

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.