Zellweger syndrome,
neonatal adrenoleukodystrophy,
infantile Refsum's disease, and classical
rhizomelic chondrodysplasia punctata are lethal
genetic disorders caused by defects in peroxisome biogenesis. We report here a characterization of the peroxisomal matrix
protein import capabilities of fibroblasts from 62 of these peroxisome biogenesis disorder patients representing all ten known complementation groups. Using an immunofluorescence microscopy assay, we identified three distinct peroxisomal
protein import defects among these patients. Type-1 cells have a specific inability to import
proteins containing the PTS1
peroxisomal targeting signal, type-2 cells have a specific defect in import of
proteins containing the PTS2 signal, and type-3 cells exhibit a loss of, or reduction in, the import of both PTS1 and PTS2
proteins. Considering that the common cellular phenotype of
Zellweger syndrome,
neonatal adrenoleukodystrophy and
infantile Refsum's disease has been proposed to be a complete defect in peroxisomal matrix
protein import, the observation that 85% (40/47) of the type-3 cell lines imported a low but detectable amount of both PTS1 and PTS2
proteins was surprising. Furthermore, different cell lines with the type-3 defect exhibited a broad spectrum of different phenotypes; some showed a complete absence of matrix
protein import while others contained 50-100 matrix
protein-containing peroxisomes per cell. We also noted certain relationships between the import phenotypes and clinical diagnoses: both type-1 cell lines were from
neonatal adrenoleukodystrophy patients, all 13 type-2 cell lines were from classical
rhizomelic chondrodysplasia punctata patients, and the type-3 import defect was found in the vast majority of
Zellweger syndrome (22/22), neonatal adrenoleukodytrophy (17/19), and
infantile Refsum's disease (7/7) patients. Our finding that all type-1 cell lines were from the second complementation group (CG2), all 13 type-2 cell lines were from CG11, and that cells from the eight remaining complementation groups only exhibit the type-3 defect indicates that mutations in particular genes give rise to the different types of peroxisomal
protein import defects. This hypothesis is further supported by correlations between certain complementation groups and particular type-3 subphenotypes: all patient cell lines belonging to CG3 and CG10 showed a complete absence of peroxisomal matrix
protein import while those from CG6, CG7, and CG8 imported some peroxisomal matrix
proteins. However, the fact that cell lines from within particular complementation groups (CG1, CG4) could have different matrix
protein import characteristics suggests that allelic heterogeneity also plays an important role in generating different import phenotypes in certain patients.(ABSTRACT TRUNCATED AT 400 WORDS)