Developmental changes of S-100 protein and glial fibrillary acidic protein in the brain in Down syndrome.

The location of the gene for the beta subunit of S-100 protein on chromosome 21 suggests that expression may be increased in trisomy 21. Astrocytes from Down syndrome and control patients were examined by immunohistochemistry for the expression of S-100 protein. Adjacent sections were reacted with antisera to glial fibrillary acidic protein to ascertain the presence or absence of astrogliosis. The developmental change in expression of S-100 protein was determined in patients ranging in age from 34 gestational weeks to 57 years. In control patients the number of S-100 protein-immunoreactive cells increased during early infancy to reach a plateau; the number stayed at this level until adulthood and then gradually declined. In Down syndrome, the pattern was similar, except that the number of S-100 protein-positive cells in the hippocampus was greater than in controls, especially during early infancy and at older ages. In the patients examined in early infancy there was no evidence of astrogliosis. However, in older patients with Down syndrome the increased number of immunoreactive cells with antisera to both S-100 protein and glial fibrillary acidic protein indicates the presence of gliosis related to occurrence of senile plaques and neurofibrillary tangles. The increased immunoreactivity of S-100 protein in early life suggests that in trisomy 21 the expression of the gene for the beta subunit may be enhanced. The significance of increased S-100 protein in relation to neural maturation in Down syndrome is unknown.