| Abstract: | Abstract— White matter and purified myelin from cerebral tissue obtained at autopsy from four phenylketonuric and five non-phenylketonuric mentally-retarded patients were analysed for lipids, DNA and protein. The lipid composition of the white matter and myelin was compared with that of a representative non-myelin component of white matter, the crude mitochondrial fraction. The total lipid content was significantly lower and the ratio of cholesterol to galactolipid was significantly higher in the white matter from the PKU patients than in that from the non-PKU patients. The lipid compositions of the myelin and ‘mitochondrial’ fraction, although differing from each other, did not exhibit appreciable differences between the PKU and non-PKU brain samples. However, the amount of myelin recovered from the brains of the PKU patients was, on the average, 40 percent lower than that recovered from non-PKU brains. The abnormal cholesterol: galactolipid ratio of PKU white matter could be accounted for by the altered proportion of myelin to non-myelin lipid components. The finding in PKU brains of a normal composition of lipids in the purified myelin and the absence of cholesterol esters in the white matter suggest that the deficiency in myelin may reflect an early arrest of myelination. |
