Peroxisome Biogenesis Disorders of the Zellweger Spectrum (PBD-ZSD) are a group of inherited genetic disorders caused by mutations in any one of 13 PEX genes. Individuals with the common PEX1-G843D mutation consistently develop a retinopathy that progresses to blindness. To test whether we could slow visual loss in these patients, we performed a proof-of-concept trial for PEX1 retinal gene augmentation therapy using our mouse model homozygous for the equivalent PEX1-G844D mutation.