Behavioral and intellectual functioning in patients with tyrosinemia type I

Introduction: In tyrosinemia type I (TT1) increased level of tyrosine and phenylalanine (both precursors of neurotransmitters), may potentially influence patients’ cognitive development. Aim of the study was to evaluate if the children during the treatment with phenylalanine- and tyrosine-restricted diet and nitisinone present with cognitive, emotional or behavioral problems and to find out whether plasma tyrosine and phenylalanine levels may have impact on this. Material and methods: Cognitive development and behavior, together with plasma tyrosine and phenylalanine levels, were analyzed in eight patients during their first five years of nitisinone treatment. Psychological examination has been done using standard diagnostic methods: the Wechsler Intelligence Scale for Children (WISC-R) and Child Behavior Checklist CBCL/4-18 (parents version). Results: The results showed that in the patients with TT1, attention deficit is not rare, and may be connected with the variation of the plasma tyrosine level. Moreover the reverse correlation between attention deficit and results from verbal scale may suggest decreased ability to verbal reasoning, comprehension, verbal expression and school difficulties. Conclusions: What is significant for the presence of attention disorders and the related difficulties in using the intellectual potential is not the level of tyrosine (high vs. low), but its changes (stability vs. instability). Therapeutic trials to stabilize the tyrosine level could alleviate the difficulties in focusing attention. Following a diet is necessary for keeping the normal level of tyrosine.