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FB2026_01
,
released March 12, 2026
This report describes peroxisome biogenesis disorder 9B (PBD9B), which is a subtype of peroxisome biogenesis disorder. The human gene implicated in this disease is PEX7, which plays an essential role in peroxisomal protein import. PEX7 is also implicated in a more severe disease, rhizomelic chondrodysplasia punctata, type 1 (RCDP1, MIM:215100). There is a single high-scoring fly ortholog, Pex7, for which RNAi targeting constructs and an allele caused by insertional mutagenesis have been generated.
The human PEX7 gene has not been introduced into flies. Functional complementation in a human cell system has been demonstrated: transfection of PEX7-null fibroblasts with Dmel\Pex7 cDNA restores thiolase import into peroxisomes, which normally occurs via the PTS2/PEX7 import pathway. This is particularly interesting, since it appears that the canonical PTS2 import pathway into peroxisomes is not present in Drosophila.
Animals homozygous for a loss-of-function mutation of Dmel\Pex7 are viable, with a small percentage dying in the pupal stage. Larvae exhibit mild neuronal phenotypes, including reduced brain size. Based on observation of increased amounts of nonesterified fatty acids (NEFAs) in mutant larvae, peroxisome function appears to be impaired.
[updated Apr. 2019 by FlyBase; FBrf0222196]
Newborns affected with Zellweger syndrome (ZS) are hypotonic, feed poorly, and have distinctive facies, seizures, and liver cysts with hepatic dysfunction. Bony stippling of the patella(e) and other long bones may occur. The neurological defects include demyelination, retinal dystrophy, hearing loss and seizures. Infants with ZS are significantly impaired and typically die during the first year of life, usually having made no developmental progress. Older children have retinal dystrophy, sensorineural hearing loss, developmental delay with hypotonia, and liver dysfunction. The clinical courses of the milder forms of peroxisome biogenesis disorder, neonatal adrenoleukodystrophy (NALD) and infantile Refsum disease (IRD), are variable and may include developmental delays, hearing loss, vision impairment, liver dysfunction, episodes of hemorrhage, and intracranial bleeding. While some children can be very hypotonic, others learn to walk and talk. The condition is often slowly progressive [from GeneReviews, Peroxisome Biogenesis Disorders, Zellweger Syndrome Spectrum, 2015.09.09].
PBD syndrome is characterized clinically by severe neurologic dysfunction, craniofacial abnormalities, and liver dysfunction. There are 4 main phenotypic classes of PBDs that were defined prior to the molecular characterization; three of them in order of severity, Zellweger syndrome, neonatal adrenoleukodystrophy (NALD), and infantile Refsum disease (IRD), form a spectrum of overlapping features. The most severely affected patients with classic Zellweger syndrome die within the first year. Zellweger syndrome is indicated by the "A" in the OMIM subtype designation; the less severe forms are indicated with a "B" in the OMIM subtype designation (BSC). The fourth class, rhizomelic chondrodysplasia punctata (RCDP1), displays a distinct PBD phenotype. [from MIM:214100; 15.08.10]
[PEROXISOME BIOGENESIS DISORDER 9B; PBD9B](https://omim.org/entry/614879)
[PEROXISOME BIOGENESIS FACTOR 7; PEX7](https://omim.org/entry/601757)
While most patients of PBD complementation group 11 manifest rhizomelic chondrodysplasia punctata (RCDP1; MIM:215100), a few have been reported with unusually mild phenotypes with longer survival, less neurologic involvement, normal or near-normal growth, and absence of rhizomelia (Braverman et al., 2002; pubmed:12325024). [from MIM:614879; 2019.04.16]
PEX7 accounts for less than 10% of Refsum disease. [Gene Reviews, Refsum Disease, https://www.ncbi.nlm.nih.gov/books/NBK1353]
This form of peroxisomal biogenesis disorder (PBD9B) is caused by homozygous or compound heterozygous mutation in the PEX7 gene. [from MIM:614879; 2019.04.16]
PEX7 encodes the cytosolic receptor for the set of peroxisomal matrix enzymes targeted to the organelle by the peroxisome targeting signal 2 (PTS2). [Gene Cards, PEX7; 2019.04.16]
One to one: 1 human to 1 Drosophila.
High-scoring ortholog of human PEX7 (1 Drosophila to 1 human). Dmel\Pex7 shares 43% identity and 56% similarity with the human gene.