A probably new entity of metabolic error of folic acid was described of an infant whose clinical and biochemical characteristics were: 1) mental retarda-tion and a marked dilatation of cerebral ventricles, 2) abnormally high serum
L. casei folate activity, 3) abnormally high levels of folate precursor in erythrocytes, and 4) a marked rise in reticulocyte count by an exogenous folate supplementation.
The results of investigation on tetrahydrofolate-dependent enzymes of liver specimens revealed a decreased activity of N
5 methyltetrahydrofolate transferase of our own patient.
It seems therefore likely that an impaired utilization of N
5 methyltetrahy-drofolate and its precursor in tissues due to a decreased activity of N
5 methyl-tetrahydrofolate transferase led to an abnormal accumulation of N
5 methyl-tetrahydrofolate and its precursor in serum and erythrocytes, and that trapping of folate compounds at an N
5 methyltetrahydrofolate level caused a functional deficiency of folates with sequence of development of a megaloblastic change in the bone marrow and of an impaired purine biosynthesis of the brain with a marked dilatation of cerebral ventricles.
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