Zellweger syndrome

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Zellweger syndrome
ICD-10	Q87.8
ICD-9	277.86, 759.8
OMIM	214100
DiseasesDB	14248
MeSH	D015211

Overview

Zellweger syndrome is one of a group of four related diseases called peroxisome biogenesis disorders (PBD), which are part of a larger group of diseases known as the leukodystrophies. These are inherited conditions that damage the white matter of the brain and also affect how the body metabolizes particular substances in the blood and organ tissues. Zellweger syndrome is the most severe of the PBDs. Infantile Refsum disease (IRD) is the mildest, and neonatal adrenoleukodystrophy and rhizomelic chondrodysplasia have similar but less severe symptoms. The PBDs are caused by defects in genes that are active in brain development and the formation of myelin, the whitish substance found in the cerebral cortex area of the brain. After birth, defects in the same genes reduce or eliminate the presence of peroxisomes – cell structures that break down toxic substances in the cells of the liver, kidneys, and brain. As a result, in Zellweger syndrome, high levels of iron and copper build up in blood and tissue and cause the characteristic symptoms of the disease. These symptoms include an enlarged liver; facial deformities such as a high forehead, underdeveloped eyebrow ridges, and deformed ear lobes; and neurological abnormalities, such as mental retardation and seizures. Infants with Zellweger syndrome also lack muscle tone, sometimes to the point of being unable to move, and may not be able to suck or swallow. Some babies will be born with glaucoma, retinal degeneration, and impaired hearing. Jaundice and gastrointestinal bleeding may also occur.

Historical Perspective

Named after Hans Zellweger, a former professor of Pediatrics and Genetics at the University of Iowa who did research into the disease.

Classification

The disorder is one of three peroxisome biogenesis disorders which are also known as the Zellweger spectrum. The other two diseases are neonatal adrenoleukodystrophy (NALD), and infantile Refsum disease (IRD)

Very long chain fatty acids are generally found in the central nervous system (brain and spinal cord) and the peroxisomes of these cells can not import the necessary degrative proteins for B-oxidation to occur.

Zellweger syndrome is one of a group of genetic disorders called peroxisomal diseases that affect brain development and the growth of the myelin sheath, the fatty covering—which acts as an insulator—on nerve fibers in the brain.

Causes

It is characterized by an individual's inability to beta-oxidize very-long chain fatty acids in the peroxisomes of the cell, due to a genetic disorder in one of the several genes involved with peroxisome biogenesis.

Several peroxins are associated with Zellweger syndrome, including 1, 2, 3, 5, 6, 12, 14, and 26.

Natural History, complications, and Prognosis

There is no cure for Zellweger syndrome, nor is there a standard course of treatment. Infections should be guarded against to prevent such complications as pneumonia and respiratory distress. Other treatment is symptomatic and supportive. The prognosis for individuals with Zellweger syndrome is poor. Death usually occurs by 6 months of age, and may be caused by respiratory distress, gastrointestinal bleeding, or liver failure.

Diagnosis

Physical Examination

The most common features of Zellweger syndrome include an enlarged liver, high levels of iron and copper in the blood stream, and vision disturbances. Some affected infants may show prenatal growth failure. Symptoms at birth may include a lack of muscle tone, an inability to move and glaucoma. Other symptoms may include unusual facial characteristics, mental retardation, seizures, and an inability to suck and/or swallow. Jaundice and gastrointestinal bleeding may also occur.

Differential diagnosis

Zellweger syndrome must be differentiated from other diseases that cause neurological manifestations in infants.

Diseases	Type of motor abnormality				Clinical findings	Laboratory findings and diagnostic tests	Radiographic findings
	Spasticity	Hypotonia	Ataxia	Dystonia
Leigh syndrome	-	-	+	+	Progressive psychomotor regression Seizures External ophthalmoplegia Lactic acidosis Vomiting	Increased lactate levels in blood and CSF Genetic testing	MRI: abnormal white matter signal in the putamen, basal ganglia, and brainstem on T2 images
Niemann-Pick disease type C	-	-	+	+	Progressive neurodegeneration Hepatosplenomegaly Systemic involvement of liver, spleen, or lung preceedes neurologic symptoms	Abnormal liver function tests Fibroblast cell culture with filipin staining	MRI: Cerebral and cerebellar atrophy Thinning of the corpus callosum
Infantile Refsum disease	-	+	+	-	Abnormalities of the optic nerve and disc Retinitis pigmentosa Sensorineural hearing loss Hepatomegaly and cirrhosis Neurologic deterioration is slower than in Zellweger syndrome or ALD	Elevated plasma VLCFA levels	--
Adrenoleukodystrophy	+	-	-	-	Cognitive and behavioral abnormalities Adrenal insufficiency Hyperpigmented skin Gonadal dysfunction Neurologic deterioration progresses at a variable rate	Elevated plasma VLCFA levels Molecular genetic testing for mutations in the ABCD1 gene	--
Zellweger syndrome	-	+	-	-	Craniofacial dysmorphism Hepatomegaly Neonatal seizures Profound developmental delay MRI findings include cortical and white matter abnormalities Neurologic deterioration is rapid and infants rarely survive beyond six months of age	Elevated plasma VLCFA levels Elevated levels of phytanic acid, pristanic acid, and pipecolic acid in plasma and fibroblasts Reduced plasmalogen in erythrocytes Molecular genetic testing for mutations in the PEX1 or PEX6 genes	--
Pyruvate dehydrogenase deficiency	+	+	+	-	Lactic acidosis Seizures Intellectual disability	Elevated lactate and pyruvate levels in blood and CSF Abnormal PDH enzymatic activity in cultured fibroblasts	--
Arginase deficiency	+	-	-	-	Hyperammonemia Encephalopathy Respiratory alkalosis	Elevated ammonia level Elevated arginine level	--
Holocarboxylase synthetase deficiency	-	+	-	-	Ketoacidosis Dermatitis Alopecia Seizures Developmental delay	Elevated levels of: Beta-hydroxyisovalerate Beta-methylcrotonylglycine Beta-hydroxypropionate Methylcitrate Tiglylglycine	--
Glutaric aciduria type 1	-	-	-	+	Episodes of metabolic decompensation and encephalopathy often precipitated by infection and fever Rarely presents in the newborn period Microencephalic macrocephaly Seizures (approximately 20 percent) Cognitive function is preserved	Elevated levels of: glutaric acid 3-hydroxyglutaric acid	MRI: Frontal and temporal atrophy
Ataxia telangiectasia	-	-	+	-	Progressive cerebellar ataxia Abnormal eye movements Oculocutaneous telangiectasias Immune deficiency Increased risk of malignancy	Elevated serum alpha-fetoprotein level Low IgA and IgG levels Lymphopenia Genetic testing for mutation in the ATM gene	--
Pontocerebellar hypoplasias	-	+	-	-	Progressive muscle atrophy Microcephaly Developmental delay	Genetic testing for PCH gene mutations	MRI : Small cerebellum and brainstem including the pons
Metachromatic leukodystrophy	-	+	+	-	Regression of motor skills Seizures Optic atrophy Reduced or absent deep tendon reflexes Intellectual disability	Deficient arylsulfatase A enzyme activity in leukocytes or cultured skin fibroblasts	--
Pelizaeus-Merzbacher	+	-	+	-	Nystagmus Cognitive impairment Onset in infancy Slowly progressive Language development may be normal	Genetic testing for mutations in PLP1 gene	MRI: White matter abnormalities
Angelman syndrome	-	-	+	-	Profound intellectual disability Postnatal microcephaly Typical abnormal behaviors (paroxysmal laughter, easily excitable)	Methylation studies and chromosome microarray to detect chromosome 15 anomalies and UBE3A mutations	--
Rett syndrome	+	-	-	+	Occurs almost exclusively in females Normal development during first six months followed by regression and loss of milestones Loss of speech capability Stereotypic hand movements Seizures Autistic features	Clinical diagnosis Genetic testing for MECP2 mutations	--
Lesch-Nyhan syndrome	+	-	-	+	Self-mutilating behavior Urinary stones due to hyperuricemia	Elevated uric acid level Abnormal enzymatic activity of HPRT in cultured fibroblasts Genetic testing for HPRT gene mutations	--
Miller-Dieker lissencephaly	+	+	-	-	Lissencephaly Microcephaly Dysmorphic features Seizures Failure to thrive	Cytogenetic testing for 17p13.3 microdeletion	--
Dopa-responsive dystonia	+	-	-	+	Onset in early childhood Symptoms worsen with fatigue and exercise	Positive response to a trial of levodopa	--

External links

• Health Link at Medical College of Wisconsin

References

• Based on http://www.ninds.nih.gov/disorders/zellweger/zellweger.htm

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