Craniosynostosis is a birth defect in which one or more of the sutures on a baby's head closes earlier than usual. The skull of an infant or young child is made up of bony plates that allow for growth of the skull. The borders at which these plates intersect are called sutures or suture lines. The sutures between these bony plates normally close by the time the child is 2 or 3 years old. Early closing of a suture causes the baby to have an abnormally shaped head and may limit brain growth.