Roentgenologic Findings in Growing Long Bones in Phenylketonuria

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Abstract
Under the direction of Dr. John Anderson, Chairman of the Department of Pediatrics, a long range study of phenylketonuria has been in progress at the University of Minnesota Hospitals. It is not the purpose of this report to dwell upon the past or forthcoming results of the various phases of the project. This information will be published elsewhere. Instead, we shall present an interesting sidelight in a preliminary form, namely, a unique bone growth pattern observed in phenylketonuric patients. In a search covering more than 350 papers dealing with phenylketonuria, as well as the roentgen literature, no reference to bone findings in this condition was discovered. Review of Clinical and Laboratory Aspects of Phenylketonuria When phenylketonuria was first described in 1934 (5), it was considered a laboratory rarity. In the interim, it has become an important medical and social problem. At least 1 per cent of mental defectives in state institutions suffer from phenylketonuria. At birth the infants appear normal. By three to six weeks of age, spill of phenylpyruvic acid in the urine occurs. The majority of the children are blond, fairskinned, and blue-eyed, and are mentally retarded. Some 33 per cent have eczema and 25 per cent have seizures, manifestations which decrease with age (9, 10). Electroencephalographic tracings are abnormal (13). In spite of the fact that most of the patients are retarded at the idiot level, approximately 1 per cent are mentally normal (2). In phenylketonuria the liver enzyme, phenylalanine hydroxylase, is deficient, thereby preventing the conversion of phenylalanine to tyrosine. This results in high blood and cerebrospinal fluid levels of I-phenylalanine. Alternative metabolic pathways develop for its disposal, and the urinary excretion of phenylketone bodies results. Normal tyrosine metabolism is also inhibited, with consequent decrease in melanin production, which probably accounts for the commonly mentioned fair complexion of these patients (3, 11). The electrophoretic pattern of the beta lipoproteins is abnormal (4). Oxygen and sugar consumption by the brain is decreased (6). Likewise, epinephrine production is disturbed. The reason for central nervous system damage secondary to high phenylalanine levels is still unknown.

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