1. Azen CG, Koch R, Friedman EG, Berlow St, Coldwell J, Krause W, Mat-alon R, McCabe E, et al (1991) Intellectual development in 12-year-old children treated for phenylketonuria. Am J Dis Child 145:35–39
2. Blaskovics ME (1986) Diagnosis in relationship to treatment of hyperphenylalaninaemia. J Inherited Metab Dis 9 [Suppl]:78–82
3. Burgard P, Armbruster M, Schmidt E, Rupp A (1995) Psychopathology of patients treated early for phenylketonuria: results of the German collaborative study of phenylketonuria. Acta Paediatr 83 [Suppl 407]: 108–110
4. Cattell RB (1963) Theory of fluid and crystallized intelligence: a critical experiment. Educ Psychol 54: 1–22
5. Collaborative study of children treated for Phenylketonuria (PKU) in the Federal Republic of Germany (1990) Eur J Pediatr [Suppl 1] 149