Determination of CSF 5-methyltetrahydrofolate in children and its application for defects of folate transport and metabolism

To describe an assay of 5-methyltetrahydrofolate (5MTHF) in the cerebrospinal fluid (CSF) of children, to determine reference values, and to report the clinical significance of this assay in metabolic disorders affecting folate transport and metabolism. CSF 5MTHF was determined by high-performance liquid chromatography with fluorescent detection in pediatric patients including one with FOLR1 gene mutation and one with methylenetetrahydrofolate reductase (MTHFR) deficiency. CSF total folate was measured using an automated analyzer. 5MTHF and total folate were determined in 188 and 93 CSF samples, respectively. CSF 5MTHF was high throughout the first six months of life and subsequently declined with age. Reference values of CSF 5MTHF and total folate were determined from 162 and 82 samples, respectively. The patient with FOLR1 gene mutation had extremely low CSF 5MTHF and total folate, though these values normalized after folinic acid supplementation. The patient with MTHFR deficiency had extremely low 5MTHF and moderately low total folate; these values were not associated and showed no significant change after folic acid supplementation. This 5MTHF assay is simple, rapid, sensitive, reliable, and cost-effective. It will aid in the diagnosis and therapeutic monitoring of metabolic disorders affecting folate transport and metabolism.