Table 1
Inherited disorders of folate transport and metabolism 3:
        Methylene-H4 folate reductase deficiency
        Functional methyltetrahydrofolate (methyl-H4 folate):
        homocysteine methyltransferase (methionine synthase) deficiency caused by cobalamin E (cblE) or G(cblG) disease
        Glutamate formiminotransferase deficiency
        Hereditary folate malabsorption
        Dihydrofolate reductase deficiency
        Methenyl-H4 folate cyclohydrolase deficiency
        Cellular uptake defects
        Primary methyl-H4 folate:homocysteine methyltransferase deficiency
Nervous system clinical features37:
    (a). Neonatal and early infancy (<3 months):
        Poor feeding
    (b) Late infancy and early childhood (>3 months–<10 years):
        Slow development
        Mental deterioration
        Spastic paresis (subacute combined degeneration)
        Extrapyramidal signs
    (c) Late childhood and early adulthood (>10 years):
        Previous mild retardation
        Mental deterioration
        Behaviour disturbance
        Myelopathy (subacute combined degeneration)