Histidinaemia.  Part III: Impact; a prospective study. 
We describe a prospective study of histidinaemia.  Probands and siblings (n = 21) with typical histidinaemia in 16 families were ascertained by newborn screening; diagnosis was confirmed by appropriate investigations in each subject; none had been treated by low histidine diet.  The median age of subjects with histidinaemia was 9.5 y (mean 10.0, SD 3.5, range 6-18).  Age-matched sib-pairs and their mothers were studied.  IQ scores (Full Scale, Verbal and Performance Scores), Visual-Motor Integration Performance (Bender Gestalt and Koppitz scores), Wide Range Achievement Test (Reading and Mathematics), school performance, and psychological history were evaluated, as well as the medical history (pregnancy, delivery, neonatal, post-natal development).  Findings were correlated with biochemical phenotype.  CNS development in histidinaemic subjects (mean and distribution of scores) was normal; outlier values did not correlate with degree of histidinaemia.  We can conclude that histidinaemia detected by newborn screening is a non-disadaptive phenotype.