Enhancement of S-100 beta protein in blood of patients with Down's syndrome.

The human gene encoding the beta subunit of S-100 protein (S-100 beta) was mapped on chromosome 21. In order to confirm the expression of gene-dosage effect of S-100 beta in patients with Down's syndrome (DS), concentrations of immunoreactive S-100 alpha and S-100 beta proteins were determined in the blood plasma and lymphocytes fraction of the patients and control subjects. Cu/Zn-superoxide dismutase (SOD), a protein that is known to show the gene-dosage effect on the trisomy of chromosome 21, also was immunoassayed in the same blood samples as control proteins. In blood plasma, S-100 beta protein as well as Cu/Zn SOD was enhanced (P less than 0.001) in the patients (160 +/- 70 pg S-100 beta/ml and 87 +/- 83 ng SOD/ml, N = 44) as compared with control individuals (76 +/- 25 pg/ml, and 18 +/- 11 ng/ml, respectively, N = 28). However, concentrations of S-100 alpha in blood plasma of DS patients were similar to those of normal subjects. Concentrations of S-100 beta in lymphocyte fractions of DS patients (24.7 +/- 10.9 ng/mg protein) were also higher (P less than 0.001) than those of control subjects (10.1 +/- 5.8 ng/mg protein). These results indicate that gene-dosage effect of S-100 beta levels are expressed in DS patients.