[Analysis of 9 patients with adolescence-onset methylenetetrahydrofolate reductase deficiency].

Objective: To explore the diagnosis and treatment of adolescence-onset methylenetetrahydrofolate reductase (MTHFR) deficiency. Methods: This was a retrospective case study. Nine patients with adolescence-onset MTHFR deficiency were diagnosed at Peking University First Hospital from January 2016 to December 2022, and followed up for more than 1 year. Their general information, clinical manifestations, laboratory tests, cranial images, MTHFR gene variants, diagnosis, treatment, and outcome were analyzed retrospectively. Results: The 9 patients came from 8 families. They had symptoms at age of 8.0 years to 17.0 years and diagnosed at 9.0 years to 17.5 years. Eight were male and 1 was female. Two patients were brothers, the elder brother developed abnormal gait at 17.0 years; and the younger brother was then diagnosed at 15.0 years of age and treated at the asymptomatic stage, who was 18.0 years old with normal condition during this study. The main manifestations of the 8 symptomatic patients included progressive dyskinesia and spastic paralysis of the lower limbs, with or without intellectual decline, cognitive impairment and behavioral abnormalities. Totally, 15 variants of MTHFR gene were identified in the 9 patients, including 8 novel variants. Five patients had brain image abnormalities. Increased plasma total homocysteine level (65-221 μmol/L) was found in all patients, and decreased to 20-70 μmol/L after treatment with betaine and calcium folinate. Besides, the 8 symptomatic patients had their behavior and cognitive problems significantly improved, with a legacy of lower limb motor disorders. Conclusions: Late-onset MTHFR deficiency can occur in adolescence. The diagnosis is usually delayed because of non-specific clinical symptoms. The test of blood total homocysteine could be used as a selective screening test. Eight novel varients of MTHFR gene were identified. Timely treatment can improve clinical condition significantly, and pre-symptomatic treatment may prevent brain damage.