Peroxisome biogenesis disorders are a heterogeneous group of human neurodegenerative diseases caused by peroxisomal metabolic dysfunction. At the molecular level, these disorders arise from mutations in PEX genes that encode proteins required for the import of proteins into the peroxisomal lumen. The Zellweger syndrome spectrum of diseases is a major sub-set of these disorders and represents a clinical continuum from Zellweger syndrome (the most severe) through neonatal adrenoleukodystrophy to infantile Refsum disease. The PEX1 gene, which encodes a cytoplasmic AAA ATPase, is the responsible gene in more than half of the Zellweger syndrome spectrum patients, and mutations in PEX1 can account for the full spectrum of phenotypes seen in these patients. In these studies, we have undertaken mutation analysis of PEX1 in skin fibroblast cell lines from Australasian Zellweger syndrome spectrum patients. A previously reported common PEX1 mutation that gives rise to a G843D substitution and correlates with the less severe disease phenotypes has been found to be present at high frequency in our patient cohort. We also report a novel PEX1 mutation that occurs at high frequency in Zellweger syndrome spectrum patients. This mutation produces a frameshift in exon 13, a change that leads to the premature truncation of the PEX1 protein. A Zellweger syndrome patient who was homozygous for this mutation and who survived for less than two months from birth had undetectable levels of PEX1 mRNA. This new common mutation therefore correlates with a severe disease phenotype. We have adopted procedures for the detection of this mutation for successful prenatal diagnosis.