High sialic acid reactivity of sugar chain structure Lewis-X in patients with mental retardation

It has been reported that platelet-derived growth factor B-chains homodimer (PDGF-BB) improves learning function of mice, and that sugar chain structure Lewis-X of N-glycosylated glycoprotein promotes PDGF-BB secretion from platelets. Based on these findings, we assumed that learning dysfunction in some patients with mental retardation might be due to abnormality in PDGF-BB metabolism and/or Lewis-X structure. No difference in the reactivity of PDGF-BB and Lewis-X was found between the serum of patients with mental retardation and that of normals. But sialic acid reactivity of the Lewis-X fraction in some patients was remarkably higher than that in other patients and in normals. These findings suggest that sialic acids in the Lewis-X fraction may have a relation to one of the causes of learning dysfunction in these patients.