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Zellweger syndrome, neonatal adrenoleukodystrophy, and infantile Refsum's disease are genetic disorders characterized by the virtual absence of catalase-positive peroxisomes and a general impairment of peroxisomal functions. Recent studies in these three disorders have provided morphologic evidence of peroxisomal "ghosts" of density 1.10 g/cm3 that contain membrane proteins but lack a majority of the matrix enzyme activities. We report here the biochemical studies in a female infant with clinical features of infantile Refsum's disease whose liver and fibroblasts contained cytosolic catalase but no catalase-positive peroxisomes. Oxidation of phytanic and pipecolic acids was severely impaired, whereas oxidation of very-long-chain fatty acids and dihydroxyacetone phosphate acyltransferase activity were only partially decreased. Immunoblot analysis showed that the three peroxisomal beta-oxidation enzymes (acyl-CoA oxidase, enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase, and 3-ketoacyl-CoA thiolase) were detectable in liver tissues. The 3-ketoacyl-CoA thiolase was of the mature form (41 kD), in contrast with other peroxisomal disorders with multiple enzyme deficiencies. The majority of these peroxisomal enzyme activities were associated with two subcellular membrane vesicle fractions lacking catalase: one had the density of normal peroxisomes (1.17 g/cm3), the other, yet undescribed, a lower density (1.137 g/cm3). This suggests that peroxisomes (density = 1.17 g/cm3) and structures with lower density (density = 1.137 g/cm3) found in this patient's cultured skin fibroblasts, although lacking catalase, contained functional peroxisomal enzymes. This distinguishes this disorder from other disorders of peroxisome biogenesis.

The peroxisomal disorders represent a group of inherited metabolic disorders that derive from defects of peroxisomal biogenesis and/or from dysfunction of single or multiple peroxisomal enzymes. Because peroxisomes are involved in the metabolism of lipids critical to the functioning of the nervous system, many of the peroxisomal disorders manifest with significant degrees of progressive psychomotor dysfunction. These disorders should be considered in the differential diagnosis of the infant with hypotonia and psychomotor delay (especially if accompanied by facial dysmorphisms, hepatomegaly, cataracts and/or retinitis, calcific stippling, short limbs, or combinations of these features), in the school-aged child with progressive neurologic dysfunction, and in adults with slowly progressive motor dysfunction. Current knowledge of peroxisomal biochemical and enzymatic processes permits precise identification of particular disorders within the peroxisomal disorder grouping. An effort should be made to identify the specific peroxisomal disorder to provide a precise explanation for neurodevelopmental deficits, to potentially prevent recurrence through genetic counseling, and to provide appropriate therapies when available.

In recent years an increasing number of inherited decreases in man has been identified in which there is an impairment of one or more peroxisomal functions. Sofar 15 different peroxisomal disorders have been identified which can be subdivided into three distinct groups depending upon whether there is a generalized (group A), multiple (group B) or single (group C) loss of peroxisomal functions. In this paper we will briefly describe the functions of peroxisomes in man which are of direct relevance for the peroxisomal disorders known up to now. Based upon the biochemical characteristics of the different peroxisomal disorders, we well describe a straightforward approach for the postnatal identification of patients suspected to suffer from a peroxisomal disorder. Furthermore, a detailed analysis of the biochemical procedures which should be used preferably, is given.

An eleven month-old boy presented clinically with craniofacial dysmorphia, severe psychomotor retardation, neurological deterioration, no response to visual and acoustic stimuli, failure to thrive, hepatomegaly and adrenal insufficiency. Specific biochemical markers for a peroxisomal deficiency disorder (Zellweger's syndrome, neonatal adrenoleukodystrophy, infantile Refsum's disease) revealed pathological results for very long chain fatty acids, phytanic acid, pristanic acid, plasmalogen biosynthesis and catalase, thus confirming the clinical diagnosis. Comparison of clinical and biochemical findings in the patient with the characteristics of the three peroxisomal deficiency disorders showed overlapping with each of these disorders, which corresponds to the current view that these three peroxisomal disorders differ only with respect to onset and severity of the clinical manifestations, but not with regard to the biochemical defects.

Peroxisomal disorders are genetic metabolic diseases with generalized, multiple, or single functional disturbances of the peroxisome. According to the extent of the functional disturbances 3 groups of diseases can be differentiated: disorders with generalized loss of peroxisomal functions (Zellweger syndrome, ZS; neonatal adrenoleukodystrophy, NALD; infantile Refsum's disease), disorders with multiple enzymatic defects (e.g. rhizomelic chondrodysplasia punctata), and disorders with a single enzymatic defect in the peroxisome, the most important being adrenoleukodystrophy/adrenomyeloneuropathy (ALD/AMN). Adult Refsum's disease, a genetic neurological disorder with phytanic acid accumulation, is due to a mitochondrial enzyme deficiency, but is often considered together with peroxisomal diseases because of phytanic acid (PHYT) accumulation in most peroxisomal diseases. The main clinical and pathological criteria of the major disorders and the biochemical parameters of their differentiation are presented. Elevated levels of very long chain fatty acids (VLCFA) and/or PHYT are the primary diagnostic markers for all peroxisomal disorders and adult Refsum's disease, respectively. Our investigations disclosed 30 ALD/AMN hemizygotes, 16 ALD/AMN heterozygotes, 8 cases of ZS/NALD and 7 patients with adult Refsum's disease. In addition, 15 cases of peroxisomal disorders were confirmed by biochemical investigations in autopsy material. With regard to peroxisomal disorders, therapeutic concepts exist only for ALD/AMN: corticosteroid substitution for adrenal insufficiency, dietary treatment, and bone marrow transplantation (BMT). Adult Refsum's disease can be treated successfully by dietary therapy. In case of dietary treatment and BMT, assay of VLCFA and/or PHYT is important for the biochemical evaluation of these therapies.

The properties and metabolic functions of peroxisomes are discussed. Classification and clinical symptoms of various diseases resulting from deficiencies of those organellae are presented. Most of the diseases involve the nervous system. The detection and determination of long-chain fatty acids (containing over 26 carbon atoms) is the principal diagnostic method in peroxisomal diseases.

Most patients with Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum disease and hyperpipecolic acidemia are characterized by a deficiency of peroxisomes. We have developed a simple cytological method for the in situ detection of genetic complementation among and between these patients who are clinically and biochemically defined as having generalized peroxisomal dysfunction. This technique should facilitate both complementation studies in these disorders and investigations into the biogenesis of peroxisomes.

The plasma of patients with inherited defects in peroxisomal biogenesis (ie, Zellweger's syndrome, infantile Refsum's disease, and neonatal adrenoleukodystrophy) shows evidence of a disturbance in the metabolism of saturated and monoenoic fatty acids with carbon chain lengths greater than 22 (VLCFA). Zellweger's syndrome plasma alone contains, in addition, increased amounts of a number of n-6 polyenoic VLCFA including 24:5, 26:5, 28:5, 30:5, and 30:6 fatty acids. These fatty acids facilitate the biochemical discrimination of Zellweger's syndrome from other related phenotypes.