From OMIMPeroxisome biogenesis disorder-1B (PBD1B) is characterized by the overlapping phenotypes of neonatal adrenoleukodystrophy (NALD) and infantile Refsum disease (IRD), which represent the milder manifestations of the Zellweger syndrome spectrum (ZSS) of peroxisome biogenesis disorders (PBDs). Initial presentation and natural history varies, with many children presenting as newborns, whereas others do not come to attention until later. Most affected children have hypotonia, but unlike Zellweger syndrome (see PBD1A, 214100) there is a degree of psychomotor development, and some patients achieve head control, sit unsupported, and may even walk independently. Many can communicate, and although language is rare, there have been children who have near normal language for age. Craniofacial anomalies are similar to but less pronounced than in Zellweger syndrome. In some individuals a leukodystrophy develops, with degeneration of myelin, loss of previously acquired skills, and development of spasticity; this may stabilize, or progress and be fatal. In PBD1B, the most common manifestations that are less apparent in ZS are sensorineural hearing loss and retinitis pigmentosa (summary by Steinberg et al., 2006). While Zellweger syndrome usually results in death in the first year of life, children with the NALD presentation may reach their teens, and those with the IRD presentation may reach adulthood (summary by Waterham and Ebberink, 2012).
Individuals with mutations in the PEX1 gene have cells of complementation group 1 (CG1, equivalent to CGE). For information on the history of PBD complementation groups, see 214100.
Genetic Heterogeneity of Peroxisome Biogenesis Disorder NALD/IRD
The phenotypic spectrum of NALD/IRD peroxisome biogenesis disorders can be caused by mutation in members of the peroxin (PEX) gene family. The PEX genes encode proteins essential for the assembly of functional peroxisomes (summary by Distel et al., 1996). PBD1B is caused by mutation in the PEX1 gene on chromosome 7q21; PBD2B (202370) is caused by mutation in the PEX5 gene (600414) on chromosome 12p13.3; PBD3B (266510) is caused by mutation in the PEX12 gene (601758) on chromosome 17; PBD4B (614863) is caused by mutation in the PEX6 gene (601498) on chromosome 6p21.1; PBD5B (614867) is caused by mutation in the PEX2 gene (170993) on chromosome 8q21.1; PBD6B (614871) is caused by mutation in the PEX10 gene (602859) on chromosome 1p36.32; PBD7B (614873)is caused by mutation in the PEX26 gene (608666) on chromosome 22q11.21; PBD8B (614877) is caused by mutation in the PEX16 gene (603360) on chromosome 11p11; PBD10B (617370) is caused by mutation in the PEX3 gene (603164) on chromosome 6q24; and PBD11B (614885) is caused by mutation in the PEX13 gene (601789) on chromosome 2p15.
See PBD1A (214100) for a phenotypic description and a discussion of genetic heterogeneity of Zellweger syndrome, which is also caused by mutation in peroxin genes. The rhizomelic chondrodysplasia subtype of PBD (RCDP1, PBD9; 215100), and a mild PBD without rhizomelia (PBD9B; 614879), are caused by mutation in the PEX7 gene (601757) on chromosome 6q23.
http://www.omim.org/entry/601539 From MedlinePlus GeneticsZellweger spectrum disorder is a condition that affects many parts of the body. Cases of Zellweger spectrum disorder are often categorizes as severe, intermediate, or mild.
Individuals with severe Zellweger spectrum disorder usually have signs and symptoms at birth, which worsen over time. These infants experience weak muscle tone (hypotonia), feeding problems, hearing and vision loss, and seizures. These problems are caused by reduced myelin, which is the covering that protects nerves and promotes the efficient transmission of nerve impulses. The part of the brain and spinal cord that contains myelin is called white matter. Reduced myelin (demyelination) leads to loss of white matter (leukodystrophy).
Children with severe Zellweger spectrum disorder also develop life-threatening problems in other organs and tissues, such as the liver, heart, and kidneys, and their liver or spleen may be enlarged. They may have skeletal abnormalities, including a large space between the bones of the skull (fontanelles) and characteristic bone spots known as chondrodysplasia punctata that can be seen on x-ray. Affected individuals can have eye abnormalities, including clouding of the lenses of the eyes (cataracts) or involuntary, side-to-side movements of the eyes (nystagmus). Severe Zellweger spectrum disorder involves distinctive facial features, including a flattened face, broad nasal bridge, high forehead, and widely spaced eyes (hypertelorism). Children with severe Zellweger spectrum disorder typically do not survive beyond the first year of life.
People with intermediate or mild Zellweger spectrum disorder have more variable features that progress more slowly than those with the severe form. Affected children usually do not develop signs and symptoms of the disease until late infancy or early childhood. Children with these intermediate and mild forms often have hypotonia, vision problems, hearing loss, liver dysfunction, developmental delay, and some degree of intellectual disability. Most people with the intermediate form survive into childhood, and those with the mild form may reach adulthood. In rare cases, individuals at the mildest end of the condition spectrum have developmental delay in childhood and hearing loss or vision problems beginning in adulthood and do not develop the other features of this disorder.
The severe, intermediate, and mild forms of Zellweger spectrum disorder were once thought to be distinct disorders. The severe form was known as Zellweger syndrome, the intermediate form was neonatal adrenoleukodystrophy (NALD), and the mild form was infantile Refsum disease. These conditions were renamed as a single condition when they were found to be part of the same condition spectrum.
https://medlineplus.gov/genetics/condition/zellweger-spectrum-disorder