A longitudinal study of phenylketonuria based on the data of the Budapest Screening Center.

Between 1975 and 1994 about 1.5 million neonates were screened by Guthrie tests at the phenylketonuria (PKU) Centre in Budapest. In this period 160 children with PKU were found. The corresponding incidence rate is about 1:9000. In a cumulative longitudinal design we investigated 56 patients with classical PKU between the ages of 3 months and 20.5 years. Treatment started at a mean age of 16.9 days (SD = 8.8). On average, pretreatment phenylalanine (Phe) levels were 1956 mumol/l (SD = 864), measured with the fluorometric method. Their Phe levels, physical growth, intellectual development, and performances in achievement tests were analysed. For the entire sample 45% of half year median Phe levels were in the recommended range, 33% represented poor dietary control, 22% were classified as intermediate. Physical growth was not significantly different from the Hungarian average. Mean verbal as well as nonverbal IQs were in the middle of the normal range. For an extended sample of 131 patients not followed longitudinally, mean recent IQ was 99.6 (SD = 16.3). Data concerning educational career were available for 107 patients. Normal schools were attended by 88 patients, 19 were in need of special elementary education. From 40 patients who had already finished elementary school, 17 underwent secondary school education, 1 is a university student, 15 are skilled workers, 4 were semi-skilled, and 4 are unemployed for reasons unrelated to their intellectual status.