Phenotype of patients with peroxisomal disorders subdivided into sixteen complementation groups

Complementation analysis in patients with the clinical phenotype of a generalised peroxisomal disorder

The generalised peroxisomal disorders (GPDs) Zellweger syndrome (ZS), neonatal adrenoleucodystrophy (NALD), and infantile Refsum's disease (IRD) are autosomal recessive disorders associated with a failure to assemble mature peroxisomes. We confirmed the diagnosis of a GPD in eight ZS and four IRD patients (GPD1 to GPD12) biochemically by measuring very long chain fatty acids, plasmalogen biosynthesis, and catalase solubility in skin fibroblasts. One further patient (BOX-1) had the clinical phenotype of ZS, but biochemical investigations indicated an isolated deficiency of peroxisomal beta oxidation. To date a total of 10 complementation groups (CGs) for the GPDs and three further CGs for isolated beta oxidation deficiencies have been identified. Most GPD patients have been shown to belong to CG-1 (Baltimore classification); among the rarer groups, CG-4 and CG-8 predominate. We performed somatic cell hybridisation experiments on strains GPD-1 to GPD-12 using plasmalogen biosynthesis as a marker for correction and found that six ZS and three IRD patients, eight of whom were of UK origin, belonged to CG-1. Strain GPD-11, a patient of UK origin with an unusual biochemical phenotype, belonged to CG-8. Strains GPD-10 and GPD-12 were derived from ZS patients of Arabian and Pakistani origin and belonged to the rarer CGs 2 and 7, respectively. Furthermore, complementation analysis using beta oxidation as a marker showed that BOX-1 had an isolated deficiency of the bifunctional protein.

Very long-chain fatty acids in diagnosis, pathogenesis, and therapy of peroxisomal disorders

Abnormally high levels of very long-chain fatty acids (VLCFA) are a feature in nine of the fifteen peroxisomal disorders that have been identified so far. Saturated VLCFA accumulate in X-linked adrenoleukodystrophy, appear to disrupt membrane structure, and may play a role in the pathogenesis of a brain inflammatory response. Dietary therapy initiated when patients are still asymptomatic may be of clinical benefit.

Neuronal migration abnormality in peroxisomal bifunctional enzyme defect

Patterns of brain dysgenesis that resemble those in the Zellweger syndrome were demonstrated in a boy with an isolated defect of the peroxisomal bifunctional enzyme. There was bilateral centrosylvian pachygyria and polymicrogyria, diffuse hemispheric hypomyelination with heterotopic neurons, Purkinje cell heterotopias, and simplified convolutions of the dentate nucleus and inferior olive. This association of Zellweger syndrome-like brain dysgenesis with a defect of a single peroxisomal enzyme provides new opportunities for the study of pathogenetic mechanisms in peroxisomal disorders.

Recent developments in peroxisome biology

Peroxisomes are subcellular organelles that are present in all eukaryotic organisms. These organelles are the focus of much contemporary interest among cellular and medical biologists--an interest which coincides with the realization of their vital role in higher organisms, their unique metabolic and biogenetic characteristics, and their widespread involvement in genetic and degenerative disease. This article reviews some of the major recent developments in peroxisome biology.

Distinction between peroxisomal bifunctional enzyme and acyl-CoA oxidase deficiencies

The clinical distinction between patients with a disorder of peroxisome assembly (e.g., Zellweger syndrome) and those with a defect in a peroxisomal fatty acid beta-oxidation enzyme can be difficult. We studied 29 patients suspected of belonging to the latter group. Using complementation analysis, 24 were found to be deficient in enoylcoenzyme A hydratase/3-hydroxyacylcoenzyme A dehydrogenase bifunctional enzyme and 5 were deficient in acyl-CoA oxidase. Elevated plasma very long-chain fatty acids (VLCFA), impaired fibroblast VLCFA beta-oxidation, decreased fibroblast phytanic acid oxidation, normal plasmalogen synthesis, normal plasma L-pipecolic acid level, and normal subcellular catalase distribution were characteristic findings in both disorders. The elevation in plasma VLCFA levels and impairment in fibroblast VLCFA beta-oxidation were more severe in bifunctional-deficient than in oxidase-deficient patients. The clinical course in bifunctional deficiency (profound hypotonia, neonatal seizures, dysmorphic features, age at death approximately 9 months) was more severe than in oxidase deficiency (moderate hypotonia without dysmorphic features, development of a leukodystrophy, age at death approximately 4 yr). Based on these findings, accurate early diagnosis of these deficiencies of peroxisomal beta-oxidation enzymes is possible.