Identification of novel mutations and sequence variation in the Zellweger syndrome spectrum of peroxisome biogenesis disorders

Abstract

Peroxisome biogenesis disorders (PBD) are a heterogeneous group of autosomal recessive neurodegenerative disorders that affect multiple organ systems. Approximately 80% of PBD patients are classified in the Zellweger syndrome spectrum (PBD-ZSS). Mutations in the PEX1, PEX6, PEX10, PEX12, or PEX26 genes are found in approximately 90% of PBD-ZSS patients. Here, we sequenced the coding regions and splice junctions of these five genes in 58 PBD-ZSS cases previously subjected to targeted sequencing of a limited number of PEX gene exons. In our cohort, 71 unique sequence variants were identified, including 18 novel mutations predicted to disrupt protein function and 2 novel silent variants. We identified 4 patients who had two deleterious mutations in one PEX gene and a third deleterious mutation in a second PEX gene. For two such patients, we conducted cell fusion complementation analyses to identify the defective gene responsible for aberrant peroxisome assembly. Overall, we provide empirical data to estimate the relative fraction of diseasecausing alleles that occur in the coding and splice junction sequences of these five PEX genes and the frequency of cases where mutations occur in multiple PEX genes. This information is beneficial for efforts aimed at establishing rapid and sensitive clinical diagnostics for PBD-ZSS patients and interpreting the results from these genetic tests. © 2008 Wiley-Liss, Inc.KEY WORDS: peroxisome biogenesis disorders, Zellweger syndrome, PBD-ZSS, neonatal adrenoleukodystrophy, infantile Refsum disease, PEX1, PEX6, PEX10, PEX12 INTRODUCTIONPeroxisomes are organelles present in almost all eukaryotic cells (Purdue and Lazarow, 2001;Schluter, et al., 2007;Wanders and Waterham, 2006). In humans, they are essential for the metabolism of branched chain and very long chain fatty acids, ether lipids, polyamines, amino acids, and glyoxylate (Schluter, et al., 2007;Steinberg, et al., 2006;Wanders and Waterham, 2006). During some of these metabolic processes, they generate and subsequently inactivate reactive oxygen species (Schrader and Fahimi, 2006). E468 Yik et al.Based on genetic, bioinformatic, and proteomic analyses, it has been estimated that at least eighty-five proteins are associated with peroxisome structure and function in humans (Schluter, et al., 2007). Peroxisome matrix proteins are synthesized on free ribosomes in the cytosol prior to import into the peroxisome. Peroxins, encoded by a family of sixteen human PEX genes (Steinberg, et al., 2004), are involved in peroxisome biogenesis with functions ranging from membrane synthesis and matrix protein import to organelle division.Peroxisomal biogenesis disorders (PBD; MIM# 601539) are inherited in an autosomal recessive manner and are characterized by impaired peroxisome assembly (Wanders and Waterham, 2005;Weller, et al., 2003). Due to their heterogeneity, PBDs had been divided into four groups: Zellweger syndrome (ZS; MIM# 214100), neonatal adrenoleukodystrophy (NALD; MIM# 202370), infantile Refsum disease (IRD; MIM# 266510), and rhiz...

Peroxisome biogenesis disorders in the Zellweger spectrum: An overview of current diagnosis, clinical manifestations, and treatment guidelines

“…PBDs are primarily caused by mutations in any of 14 different PEX genes, which code for peroxins, proteins involved in peroxisome assembly [5,7]. While mutations in PEX1 account for nearly 70% of all PBD-ZSD cases, another 26% of cases are caused by mutations in PEX6 , PEX10 , PEX12 , or PEX26 , with the majority of these cases involving PEX6 mutations [8,9]. …”

Peroxisomes in cardiomyocytes and the peroxisome / peroxisome proliferator-activated receptor-loop

“…In 1973, Goldfischer et al discovered that in hepatocytes derived from Zellweger patients functional peroxisomes were absent and mitochondria displayed an altered morphology bearing an abnormally dense matrix and an enlarged intracristal space (18). Children affected by the Zellweger syndrome display a plethora of pathologies and symptoms, including impaired brain development, craniofacial abnormalities, chondrodysplasia punctata, hypotonia, development of liver cirrhosis and, in the severest form, die within the first year of life (23).…”

Spectrum ofPEX6mutations in Zellweger syndrome spectrum patients

“…The PEX6 sequences were compared to the reference sequence of PEX6 (GenBank accession number NM_000287.3) with nucleotide numbering starting at the first adenine of the translation initiation codon ATG. 1 Mutation is mentioned in the dbPEX database (www.dbPEX.org) (Yik et al, 2009) Among the 47 novel mutations identified in our cohort, there were 11 mutations located in splice junction sequences. The c.1047-1G>A mutation was found homozygous in 2 different cell lines.…”