Alterations in myelin formation in fetal brains of twins

Abstract

Insufficient nutrition is known to lead to disturbances in postnatal myelin formation. This study aims to demonstrate that early myelination is altered in human twin pregnancies. Five brains of twins with a symmetric blood supply and three brains of twins with chronic fetal-fetal transfusion syndrome (one hypervolemic acceptor and two hypoxemic donors) were investigated and compared with six brains of singletons. The globus pallidus, where myelination normally starts within the prosencephalon, was studied immunohistochemically using antibodies against myelin basic protein (MBP) and with the aid of electron microscopy. In twins and donors, MBP-immunostained somata of myelin-forming oligodendrocytes were packed densely within the globus pallidus, whereas in singletons and acceptors an intense fibrous immunoreactivity was observed. Electron micrographs revealed noncompacted myelin in twins, whereas in singletons the multilaminar structure of compact myelin was observed. The results demonstrate a distinct qualitative alteration in myelination because of nutritional insufficiency during pregnancy. The lack of MBP-positive fibers (i.e., compact myelin sheaths) may be correlated to impaired maturation of oligodendroglia. The alterations described here may reflect a delayed incorporation of MBP into the processes so that the formation of compact myelin is retarded.