The Zellweger spectrum is a group of conditions that have overlapping signs and symptoms and affect many parts of the body. This group of disorders includes Zellweger syndrome, neonatal adrenoleukodystrophy (NALD), and infantile Refsum disease. These conditions were once thought to be distinct disorders but are now considered to be part of the same disease spectrum. Zellweger syndrome is the most severe form of the Zellweger spectrum, NALD is intermediate in severity, and infantile Refsum disease is the least severe form.
Mutations in the PEX1 gene are the most common cause of the Zellweger spectrum and are found in nearly 70 percent of affected individuals. The prognosis for individuals with Zellweger syndrome is poor. Death usually occurs within 6 months after onset, and may be caused by respiratory distress, gastrointestinal bleeding, or liver failure.