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
Clinical sign Prevalence
Megaloblastic anemia Developmental delay Seizures
Speech abnormalities 1 Gait abnormalities
Peripheral neuropathy Apnea Biochemical findings
Red blood cell folate
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