Maternal serum S100 protein in normal and Down syndrome pregnancies

Protein S100 is a low molecular weight (10-12 kD) calcium-binding protein the beta subunit of which is coded for at the 22.2-22.3 region of the long arm of chromosome 21. This region has also been shown to be responsible for the phenotypic expression of Down syndrome. Previous studies demonstrated increased immunoreactivity to protein S100 in brain tissue from adults with Down syndrome. We have previously observed a higher concentration of S100 protein in the fetal blood of trisomy 21 fetuses compared with normal subjects. The aim of this study was therefore to investigate the use of measuring S100 protein concentration in maternal blood for Down syndrome screening. Maternal blood was taken at the time of chorionic villus sampling or cordocentesis (11-38 weeks' gestation) for fetal karyotyping. Protein S100 was measured by a two-site immunoradiometric assay (S-100 IRMA, Sangtec). There was no significant difference in the concentration of maternal S100 protein between normal and trisomy 21 pregnancies (p<0.10). Moreover, there was no significant association between maternal serum S100 protein concentration and gestational age (r(s)=0.27, p=0.07), maternal age (r(s)=-0.17, p=0.7) or maternal weight (r(s)=-0.013, p=0.9). This study shows that measurement of maternal serum S100 protein concentration does not appear to have a value in Down syndrome screening.