Zellweger syndrome


Zellweger syndrome

Description, Causes and Risk Factors:

A metabolic disorder with neonatal onset, characterized by distinctive facies, muscular hypotonia, hepatomegaly with jaundice, renal cysts, epiphyseal stippling of the patellae, cerebral dysmyelination, and neuronal migration defects and psychomotor retardation; there is a perturbation in peroxisomal biogenesis; autosomal recessive inheritance, caused by mutation in any one of several peroxin (PEX) genes on chromosome 6, 7, 8, or 12.

Zellweger syndrome is one of a group of four related diseases called peroxisome biogenesis disorders (PBD). The diseases are caused by defects in any one of 13 genes, termed PEX genes, required for the normal formation and function of peroxisomes. The PBDs are divided into two groups: Zellweger spectrum disorders and Rhizomelic Chondrodysplasia Punctua spectrum. The Zellweger spectrum is comprised of three disorders that have considerable overlap of features. These include Zellweger syndrome (ZS, the most severe form), neonatal adrenoleukodystrophy (NALD), and Infantile Refsum disease (IRD, the least severe form).

Peroxisomes are cell structures that break down toxic substances and synthesize lipids (fatty acids. oils, and waxes) that are necessary for cell function. Peroxisomes are required for normal brain development and function and the formation of myelin, the whitish substance that coats nerve fibers. They are also required for normal eye, liver, kidney, and bone functions. Zellweger spectrum disorders result from dysfunctional lipid metabolism, including the over-accumulation of very long-chain fatty acids and phytanic acid, and defects of bile acids and plasmalogens -- specialized lipids found in cell membranes and myelin sheaths of nerve fibers. Symptoms of these disorders include an enlarged liver; characteristic facial features such as a high forehead, underdeveloped eyebrow ridges, and wide-set eyes; 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 also may occur.

The prognosis for infants with Zellweger syndrome is poor, with the majority of infants failing to survive their first six months of life; they usually die from gastrointestinal bleeding, respiratory distress, or liver failure. People with Zellweger syndrome often do not live more than a year after they are diagnosed. Because of this, genetic counseling and prenatal diagnosis are commonly given high-priority for parents who are either identified or concerned that they might be at risk of having a child with Zellweger syndrome.

Symptoms:

Symptoms may include:

Zellweger syndrome

    Head and face - enlarged head, high forehead, large anterior fontanelle ("soft spot"), malformed ear lobes, flat-looking face.

  • Brain and nervous system - abnormal brain development leads to seizures, hearing and vision impairment, profound mental retardation and developmental delay, diminished or absent reflexes.

  • Liver - enlarged liver with impaired function, jaundice.

  • Kidneys - renal cysts, hydronephrosis.

  • Muscles and bones - very low muscle tone (hypotonia), bone defects in the hands, legs, and feet.

Diagnosis:

The distinctive shape of the head and face of the infant born with Zellweger syndrome provides a clue to the diagnosis. Zellweger syndrome causes the build-up of very-long-chain fatty acids (VLCFA), so a test for VLCFA can help confirm the diagnosis. This and other highly specialized biochemical and genetic tests can be done at certain testing centers.

Parents should receive genetic counseling, since Zellweger syndrome is inherited in a autosomal recessive manner. This means that both parents are carriers of the defective gene, and each future child has a 25% chance of being born with Zellweger syndrome.

In addition to genetic tests involving the sequencing of PEX genes, biochemical tests have proven highly effective for the diagnosis of Zellweger syndrome and other peroxisomal disorders. Typically, Zellweger syndrome patients show elevated very long chain fatty acids in their blood plasma. Cultured primarily skin fibroblasts obtained from patients show elevated very long chain fatty acids, impaired very long chain fatty acid beta-oxidation, phytanic acid alpha-oxidation, pristanic acid alpha-oxidation, and plasmalogen biosynthesis.

Treatment:

There is no cure for Zellweger syndrome, nor is there a standard course of treatment. Since the metabolic and neurological abnormalities that cause the symptoms of Zellweger syndrome are caused during fetal development, treatments to correct these abnormalities after birth are limited. Most treatments are symptomatic and supportive.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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