PEX1 — Peroxisomal biogenesis factor 1
The PEX1 gene provides instructions for making a protein that is crucial for the formation and function of peroxisomes. Peroxisomes are small compartments within cells that break down toxic substances and fatty acids, and help build important fats needed for the brain and lungs. When the PEX1 gene is mutated, peroxisomes cannot form properly or function normally. This leads to a buildup of toxic substances and a shortage of essential fats in the body. As a result, patients can experience a range of severe health issues, including brain development problems, vision and hearing loss, liver dysfunction, and weak muscle tone. The severity of these symptoms varies widely depending on the specific mutation, ranging from the severe Zellweger syndrome to milder forms like Heimler syndrome.
Gene description: PEX1 is a gene that encodes a member of the AAA ATPase family, which is essential for peroxisome biogenesis. Mutations in this gene are the most common cause of Zellweger spectrum disorders, a group of conditions characterized by severe neurological and metabolic defects.
Patient and family guide: The PEX1 gene provides instructions for making a protein that is crucial for the formation and function of peroxisomes. Peroxisomes are small compartments within cells that break down toxic substances and fatty acids, and help build important fats needed for the brain and lungs. When the PEX1 gene is mutated, peroxisomes cannot form properly or function normally. This leads to a buildup of toxic substances and a shortage of essential fats in the body. As a result, patients can experience a range of severe health issues, including brain development problems, vision and hearing loss, liver dysfunction, and weak muscle tone. The severity of these symptoms varies widely depending on the specific mutation, ranging from the severe Zellweger syndrome to milder forms like Heimler syndrome.
Gene function: The PEX1 protein forms a heteromeric complex with PEX6, anchored to the peroxisomal membrane by PEX26. This AAA-ATPase complex mediates the ATP-dependent extraction and recycling of the PEX5 receptor from peroxisomal membranes, an essential step for the import of matrix proteins into peroxisomes.
Protein structure: PEX1 is a 147-kDa protein comprising 1,283 amino acids. It contains two N-terminal domains (N1 and N2) followed by two AAA cassettes (D1 and D2 domains), each consisting of a large nucleotide-binding subdomain and a smaller alpha-helical bundle subdomain.
Molecular function: At the molecular level, PEX1 functions as an ATP-dependent protein dislocase. It forms a double-ring AAA+ ATPase heterohexameric complex with PEX6. This complex physically interacts with mono-ubiquitinated PEX5, a receptor that delivers proteins into the peroxisome. By hydrolyzing ATP, the PEX1/PEX6 complex provides the mechanical force required to unfold and extract PEX5 from the peroxisomal membrane, allowing it to be recycled for subsequent rounds of protein import.
Mutation spectrum: The mutation spectrum of PEX1 includes missense, nonsense, frameshift (insertions/deletions), and splice site mutations. The most common mutations are the missense mutation c.2528G>A (p.Gly843Asp), which is associated with milder phenotypes, and the frameshift insertion c.2097insT, which leads to a premature stop codon and causes severe disease.
Clinical significance: Mutations in PEX1 cause Peroxisome Biogenesis Disorders (PBDs), specifically the Zellweger spectrum disorders (ZSDs) and Heimler syndrome. Severe mutations (like null alleles) abolish PEX1 function, leading to Zellweger syndrome, which is fatal in infancy. Milder missense mutations allow residual protein function, resulting in less severe phenotypes like Neonatal Adrenoleukodystrophy (NALD), Infantile Refsum Disease (IRD), or Heimler syndrome, which feature progressive vision and hearing loss.
Inheritance: Autosomal Recessive
Chromosomal location: 7q21.2
Research and therapeutic approaches: Current therapeutic approaches are mostly supportive, but experimental treatments are under investigation. These include gene augmentation therapy using AAV vectors to deliver functional PEX1 to the retina to prevent vision loss. Other approaches include small molecule therapies like arginine and betaine to improve peroxisomal assembly, and drugs targeting pexophagy (e.g., hydroxychloroquine).