Impaired myelination of the human hippocampal formation in Down syndrome

• Published in: International journal of developmental neuroscience 2012-04, Vol.30 (2), p.147-158
• Main Authors: Ábrahám, Hajnalka, Vincze, András, Veszprémi, Béla, Kravják, András, Gömöri, Éva, Kovács, Gábor G., Seress, László
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Aged; Archicortex; Axonal development; Child; Child, Preschool; Dentate gyrus; Down Syndrome - genetics; Down Syndrome - pathology; Down Syndrome - physiopathology; Female; Hippocampus - abnormalities; Hippocampus - growth & development; Hippocampus - pathology; Humans; Infant; Infant, Newborn; Male; Middle Aged; Myelin basic protein; Myelin Sheath - genetics; Myelin Sheath - pathology; Nerve Fibers, Myelinated - pathology; Ontogenesis; Trisomy 21; Young Adult
• ISSN: 0736-5748; 1873-474X
• DOI: 10.1016/j.ijdevneu.2011.11.005

► We studied myelination in the human hippocampal formation in Down syndrome. ► Myelination was studied with immunohistochemistry detecting myelin basic protein. ► Delay in myelination was observed in Down syndrome compared to controls. ► Impaired myelination in Down syndrome was the most striking in the dentate hilus. ► Contribution of impaired myelination in mental retardation of Down syndrome. Myelination is considered as one of the last steps of neuronal development and is essential to the physiologically matured function of afferent and efferent pathways. In the present study, myelin formation was examined in the human fetal, postnatal and adult hippocampal formation in Down syndrome and in age-matched controls with immunohistochemistry detecting a protein component of the myelin sheath, the myelin basic protein synthesized by oligodendroglial cells. Myelination is mainly a postnatal event in the hippocampal formation of both healthy controls and in patients with Down syndrome. In patients with Down syndrome the sequence of myelination of the hippocampal formation followed a similar developmental pattern to that in controls. However, myelin formation was generally delayed in Down syndrome compared to age-matched controls. In addition, in the hilus of the dentate gyrus a decreased density of myelinated axons was detected from the start of myelination until adulthood. The majority of local axons (mossy fibers) are not myelinated in the hilar region and myelinated fibers arriving in the hilus come mainly from the subcortical septal nuclei. Since intact septo-hippocampal connections are necessary for memory formation, we hypothesize that decreased myelination in the hilus may contribute to the mental retardation of Down syndrome patients.