Inborn Errors of Folate Transport and Metabolism

Inborn errors include hereditary folate malabsorption, methylene-tetrahydrofolate reductase (MTHFR) deficiency, and glutamate formiminotransferase deficiency. In addition to these rare severe deficiencies, polymorphisms in the MTHFR gene have been implicated with neural defects and vascular thrombosis. Table 4-7 lists the clinical and biochemical features of inherited defects of folate metabolism.

Hereditary Folate Malabsorption (OMIM 229050)

Hereditary folate malabsorption (congenital malabsorption of folate) is due to a rare autosomal recessive trait and is characterized by megaloblastic anemia, chronic or recurrent diarrhea, mouth ulcers, failure to thrive, and usually loss of developmental milestones, seizures, and progressive neurologic deterioration. The most important diagnostic feature is megaloblastic anemia in the first few months of life, associated with low serum, red cell, and cerebrospinal fluid folate levels.

All patients have an abnormality in the absorption of oral folic acid or of reduced folates. They may have an elevated excretion of formiminogiutamic (FIGLU) acid

Table 4-7. Clinical and Biochemical Features of Inherited Defects of Folate Metabolism

Hereditary folate malabsorption

Methylene-H4 folate reductase deficiency

Glutamate formiminotransferase deficiency

Functional methionine synthase deficiency

CblE

CblG

Clinical sign Prevalence

Megaloblastic anemia Developmental delay Seizures

Speech abnormalities 1 Gait abnormalities

Peripheral neuropathy Apnea Biochemical findings

Homocystinuria/homocysteinemia

Hypomethioninemia

Formininoglutamic aciduria

Folate absorption

Serum Cbl

Serum folate

Red blood cell folate

13 cases

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