The dietary treatment of phenylketonuria

Abstract

The results of treating 10 phenylketonurias with a diet low in phenylalanine are described. In almost every case there was a sharp and significant rise in I.Q. The I.Q. continued to rise, the mental age plotted against chronological age showing a point of inflexion at the time the diet was started. An infant treated from the age of 5 weeks has remained at I.Q. 88 for nearly two years, indicating that relatively slight deterioration had occurred during the five weeks before treatment. Mental deterioration (dementia) proceeds most rapidly in untreated cases during the first weeks of life, then gradually slows down, but is still continuing appreciably at 2 years of age. As it seems likely that mental deterioration in this condition can be prevented by early treatment, we suggest that every infant's urine be tested with ferric chloride at the age of 21 days (though this age may have to be modified), and treatment instituted immediately if a positive reaction is obtained. It is important to keep the blood phenylalanine concentration at the normal level. If it is too high the child's progress slows down measurably, if too low, the child ceases to grow or thrive. The diet must supply all essential nutrients. The success attending the use of this diet confirms the theory that the mental deficiency in phenylketonuria is the result of intoxication by phenylalanine or one of its abnormal metabolites.