To confirm that the variants found in PEX1 and PEX6 are the cause of the aberrant peroxisomal phenotype, we performed a genetic complementation assay. We cultured fibroblasts of individuals F1-II:3 and F5-II:2 at 40°C and then transfected these with control PEX1 and PEX6 cDNAs. The introduction of PEX1 cDNA rescued the impaired peroxisome biogenesis in cells from individual F1-II:3, and PEX6 cDNA rescued peroxisome biogenesis in cells from individual F5-II:2 (complementation in 14% or 20% of cells, respectively; Figure S4). These results confirm that the variants in PEX1 and PEX6 are the cause of the peroxisomal defects in the individuals with HS.