[Intellectual development of phenylketonuria children treated early--a longitudinal study. 10 years' concomitant psychological study in The Netherlands].

Since 1st September 1974 almost all newborns in The Netherlands have been screened for phenylketonuria (PKU). Data collected between then and 1 October 1984 are presented, with respect to the intellectual functioning of 69 patients who received early treatment for PKU. Wherever possible, psychological testing was carried out at four key ages, namely 1.0 years, 2.0 years, 4.6 years, 6.6 years. The results of the tests revealed no differences in the mental levels of these patients and healthy children at any of the key ages. Also no sex differences at key ages 1 and 2 years related to this variable were found. The longitudinal course of the intellectual development in the first four and a half years was stable. The necessity for the continuation of screening and the collection of psychosocial data is discussed.