Intelligent quotient of late treated phenylketonuric patients: is brain damage still preventable?

Abstract

Over the past 30 years and since the first trial to treat phenylketonuria (PKU) by Horst Bickel and his coworkers, the dietary treatment of PKU has produced a generation of adult women with PKU who have minimal cognitive deficits and are now of child-bearing age. If PKU is detected early enough in infancy, mental retardation can be prevented by giving a diet containing a restricted amount of phenylalanine. The principle of therapy is that all newborn babies with phenylalanine concentration of 360 µmol or above are to be treated as early as possible to achieve a higher mental function in terms of intelligence quotient, blood phenylalanine levels should be maintained in the range of 120 - 360 µmol/l. Subnormal as well as high phenylalanine levels are to be avoided. In the last few years there are increasing published articles on late treated PKU patients. In these patients, the mean IQ was 57. For those treated after 2 months of age, recent studies have suggested that approx. 23% of those children have normal IQ. In our hospital most of our cases were late treated (15 patients out of 22), the age at which treatment was started ranges from 2 weeks to 9 years.  It is noted that those patients who were diagnosed before 2 years of age (6 children) and were on strict phenylalanine low diet with a phenylalanine maintained less than 4mg/dl have a normal IQ (75 or above) (6 patients), one child  has difficulty in speech, 2 children  had border line IQ (above 70 and less than 75), two children had moderate learning difficulties (IQ above 35 and below 50), 4 children had severe learning difficulties (IQ above 20 and less than 35 of which two of them diagnosed before 2 years of age.