Zellweger syndrome: One of a group of related diseases called peroxisome biogenesis disorders (PBD), inherited conditions that damage myelin in the brain and also affect the metabolism of particular substances. Features include enlargement of the liver, high levels of iron and copper in the blood, and vision disturbances. It can be caused by mutations in a number of different genes. There is no cure for Zellweger syndrome. The prognosis is poor, with death usually occurring within 6 months.