Zellweger syndrome belongs to a group of diseases called peroxisome biogenesis disorders (PBD). The diseases are caused by defects in any one of the PEX genes that are required for the normal formation and function of peroxisomes.

Peroxisomes are cell structures that breakdown 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 also are required for normal eye, liver, kidney, and bone functions.

The PBDs are divided into two groups:

1. Zellweger spectrum disorders
2. Rhizomelic Chondrodysplasia Punctua spectrum

The Zellweger spectrum is comprised of three disorders that have considerable overlap of features:

1. Zellweger syndrome (the most severe form)
2. Neonatal adrenoleukodystrophy (NALD)
3. Infantile Refsum disease (the least severe form)

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
• Neurological abnormalities such as cognitive impairment and seizures

Infants will 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.

There is no cure for Zellweger syndrome, nor is there a standard course of treatment. Most treatments are symptomatic and supportive.