Infantile type of homocystinuria with N5,10-methylenetetrahydrofolate reductase defect.

Two infants of homocystinuria with a defective activity of the N5,10-methylenetetrahydrofolate reductase in the liver, kidney, brain and/or leukocytes were reported. Contrary to four cases with similar biochemical defects reported up to date, the two cases of ours demonstrated peculiar clinical features characterized by an early onset in infancy, fits of apnea and seizures, downhill course with coma, and death within one year of life. Thus "an infantile type" of this disorder was advanced as a new clinical entity. Assay for the N5,10-methylenetetrahydrofolate reductase activity using peripheral leukocytes was established and might be useful for a diagnosis of this disorder and also for detection of heterozygotes.