been made. The extent of signs is strongly dependent on the extent of white matter damage: minor damage leads to only minor deficits or delays, while significant white matter damage can cause severe problems with motor coordination or organ function. Some of the most frequent signs include delayed motor development, vision deficits, apneas, low heart rates, and seizures. Delayed motor development Delayed motor development of infants affected by PVL has been demonstrated in multiple studies. One of the earliest markers of developmental delays can be seen in the leg movements of affected infants, as early as one month of age. Those with white matter injury often exhibit "tight coupling" of leg joints (all extending or all flexing) much longer than other infants (premature and full-term). Additionally, infants with PVL may not be able to assume the same positions for sleeping, playing, and feeding as premature or full-term children of the same age. These developmental delays can continue throughout infancy, childhood, and adulthood. Vision deficits Premature infants often exhibit visual impairment and motor deficits in eye control immediately after birth. However, the correction of these deficits occurs "in a predictable pattern" in healthy premature infants, and infants have vision comparable to full-term infants by 36 to 40 weeks after conception. Infants with PVL often exhibit decreased abilities to maintain a steady gaze on a fixed object and create coordinated eye movements. Additionally, children with PVL often exhibit nystagmus, strabismus, and refractive error. Seizures Occurrence of seizures is often reported in children with PVL. In an Israel-based study of infants born between 1995 and 2002, seizures occurred in 102 of 541, or 18.7%, of PVL patients. Seizures are typically seen in more severe cases of PVL, affecting patients with greater amounts of lesions and those born at lower gestational ages and birth weights. Causes Predisposing factors Those generally considered to be at greatest risk for PVL are premature, very low birth-weight infants. It is estimated that approximately 3-4% of infants who weigh less than have PVL, and 4-10% of those born prior to 33 weeks of gestation (but who survive more than three days postpartum) have the disorder. Gestational CMV infection also produces PVL in neonates. Injury pathway Two major factors appear to be involved in the development of PVL: (1) decreased blood or oxygen flow to the periventricular region (the white matter near the cerebral ventricles) and (2) damage to glial