Morphologic Studies in a Patient with Homocystinuria due to 5,10-Methylenetetrahydrofolate Reductase Deficiency

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Abstract
Extract: Biochemical and morphologic studies on a patient with homocystinuria due to a deficiency of 5,10-methylenetetrahydrofolate reductase (EC. 1.1.1.68) were performed. The concentrations of homocystine in the patient's plasma and urine were 2.97 μmol/dl and 44.67 μmol/24 hr, respectively. Activities of 5,10-methylenetetrahydrofolate reductase (expressed as nanomoles of formaldehyde formed per hr per mg of protein) in cultured skin fihroblasts and liver tissue were 0.53 (control: 5.14) and 0.00 (control: 13.80), respectively. The major abnormalities were found in the arterial bed. consisting of intimal hyperplasia, fragmentation, and disruption of elastic lamellae and subcellular changes in the endothelial cells. Extensile thrombosis was observed. The brain and the liver also showed widespread pathologic changes. In the former, neuronal loss and cellular damage were prominent and extensive. Diffuse demyelination with moderate astrocytosis was found; but demyelination was out of proportion to the vascular changes. Hirano bodies in the cortical neurons and crystalline and lamellar bodies in the Purkinje cells were observed. In the liver, there were fatty change and mild to moderate portal fibrosis. Bizarre, giant mitochondria and membrane-bound multivesicular bodies were found. Mild pathologic changes were also observed in the striated muscles and the kidneys. Focal fragmentation, disruption, and smearing of the Z discs and disorganization of the myofilaments were found in the skeletal muscles. The kidneys showed shrunken glomeruli, thickened basement membranes, and swelling of epithelial as well as endothelial cells. Speculation: The morphologic abnormalities under light or electron microscopy in this patient with 5,10-methylenetetrahydrofolate reductase deficiency were strikingly similar to those reported in patients with cystathionine-β-synthase deficiency and with N5-methyltetrahydrofolate homocystine methyltransfcrase deficiency. The common denominator in all these disorders is homocystinemia. It is postulated that the widespread vascular lesions are produced by the “toxic” effect of homocystine and that the pathologic changes in other organs are the result of ischemia and thrombosis as well as a possible direct effect of homocystine.