Zellweger syndrome is an autosomal recessive systemic disorder characterized clinically by severe neurologic dysfunction, craniofacial abnormalities, and liver dysfunction, and biochemically by the absence of peroxisomes. Most severely affected individuals with classic Zellweger syndrome phenotype die within the first year of life (summary by Wanders, 2004).
'Zellweger syndrome' is the prototype of a large group of peroxisomal disorders, which can be classified into 2 main groups: (1) disorders of peroxisome biogenesis and (2) single peroxisomal enzyme deficiencies (see 264470). The peroxisome biogenesis disorders (PBDs) fall into
4 main phenotypic classes. Three of them, Zellweger syndrome, neonatal adrenoleukodystrophy (NALD), and infantile Refsum disease (IRD), have multiple complementation groups and form a spectrum of overlapping features, with the most severe being the Zellweger syndrome and the least severe infantile Refsum disease. The fourth group, rhizomelic chondrodysplasia punctata (RCDP1; 215100), is a distinct PBD phenotype (summary by Moser et al., 1995, Wanders, 2004).
Heimler syndrome, a rare autosomal recessive disorder encompassing sensorineural hearing loss, enamel hypoplasia of the secondary dentition, and nail abnormalities, represents a discrete phenotypic entity at the mildest end of the PBD spectrum (Ratbi et al., 2015).
Genetic Heterogeneity of Zellweger Syndrome
Zellweger syndrome (denoted by the suffix 'A' in the
symbol) is a genetically heterogeneous disorder and can be caused by mutation in any one of several genes, known as pexins, involved in peroxisome biogenesis. The pexin (PEX) genes encode proteins essential for the assembly of functional peroxisomes (summary by Distel et al., 1996). Forms of Zellweger syndrome include PBD1A, caused by mutation in the PEX1 gene on chromosome 7q21; PBD2A (214110), caused by mutation in the PEX5 (600414) gene on chromosome 12p13; PBD3A (614859), caused by mutation in the PEX12 (601758) gene on chromosome 17; PBD4A (614862), caused by mutation in the PEX6 (601498) gene on chromosome 6p21; PBD5A (614866), caused by mutation in the PEX2 (170993) gene on chromosome 8q21; PBD6A (614870), caused by mutation in the PEX10 (602859) gene on chromosome 1p36; PBD7A (614872), caused by mutation in the PEX26 (608666) gene on chromosome 22q11; PBD8A (614876), caused by mutation in the PEX16 (603360) gene on chromosome 11p12; PBD10A (614882), caused by mutation in the PEX3 (603164) gene on chromosome 6q23-q24; PBD11A (614883), caused by mutation in the PEX13 (601789) gene on chromosome 2p15; PBD12A (614886), caused by mutation in the PEX19 (600279) gene on chromosome 1q22; and PBD13A (614887), caused by mutation in the PEX14 gene (601791) on chromosome 1p36.2.
Mutation in the pexin genes also causes the less severe phenotypes of neonatal adrenoleukodystrophy (NALD) and infantile Refsum disease (IRD); see PBD1B (601539) for a phenotypic description and discussion of genetic heterogeneity of these PBDs.
Heimler syndrome-1 (HMLR1; 234580) and -2 (HMLR2; 616617) are caused by mutation in the PEX1 and PEX6 genes, respectively.
The rhizomelic chondrodysplasia subtype of PBD (RCDP1, PBD9; 215100), and a PBD without rhizomelia (PBD9B; 614879), are caused by mutation in the PEX7 gene (601757) on chromosome 6q22-q24.
In addition to the defects in peroxisome assembly, Distel et al. (1996) noted that peroxisomal disorders include a number of single peroxisomal enzyme deficiencies: X-linked adrenoleukodystrophy (ALD; 300100), acyl-coenzyme A oxidase deficiency (264470), DHAPAT deficiency (222765), alkyl-DHAP synthase deficiency (600121), glutaric aciduria type III (231690), classic Refsum disease (266500), hyperoxaluria type I (259900), and acatalasia (115500). A peroxisomal and mitochondrial fission defect results in a lethal encephalopathy (EMPF; 614388). [from
OMIM]