Serum levels of neural protein S-100B in phenylketonuria

Background: Serum neural protein S-100B concentration is considered as a marker of CNS lesions. Phenylketonuria (PKU) is a metabolic disorder characterized by high phenylalanine (Phe) levels in blood and foci of myelin absence in the CNS of untreated patients. Aim: To evaluate S-100B blood levels in PKU patients. Methods: Twenty-five (N = 25) PKU patients of comparable age, who were diagnosed by neonatal screening and “followed up” in our Inborn Error of Metabolism Department, were divided into two groups: group A (N = 13) with almost normal Phe levels and group B (N = 12) “off diet” with high Phe concentrations. Their MRI examinations were normal 12–14 months before the beginning of the study. Twenty-three (N = 23) healthy children were the controls. Serum S-100B levels, measured with an immunoluminometric assay, were greatly elevated in the group B (0.48 ± 0.6 μg/l) as compared to those of group A (0.16 ± 0.4 μg/l, P< 0.001) and controls (0.10 ± 0.02, P< 0.001). Positive correlation was found between S-100B and Phe blood concentration (r = 0.46, P< 0.01). Foci of myelin absence in MRIs were observed in 1/13 of group A and in 10/12 of group B at the end of this study. Conclusions: (a) Serum S-100B protein level, for the first time evaluated in PKU, was positively correlated with Phe blood level in PKU patients. (b) S-100B blood estimation could be a useful peripheral marker of CNS lesions in patients with demyelinated disease such as PKU.