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The saturated branched chain fatty acid, phytanic acid, a degradation product of chlorophyll, accumulates in Refsum disease, an inherited peroxisomal disorder with neurological clinical features. To elucidate the pathogenic mechanism, we investigated the influence of phytanic acid on cellular physiology of rat hippocampal astrocytes. Phytanic acid (100 microM) induced an immediate transient increase in cytosolic Ca2+ concentration, followed by a plateau. The peak of this biphasic Ca2+ response was largely independent of extracellular Ca2+, indicating activation of cellular Ca2+ stores by phytanic acid. Phytanic acid depolarized mitochondria without causing in situ swelling of mitochondria. The slow decrease of mitochondrial potential is not consistent with fast and simultaneous opening of the mitochondrial permeability transition pore. However, phytanic acid induced substantial generation of reactive oxygen species. Phytanic acid caused astroglia cell death after a few hours of exposure. We suggest that the cytotoxic effect of phytanic acid seems to be due to a combined action on Ca2+ regulation, mitochondrial depolarization, and increased ROS generation in brain cells.

The 3-methyl-branched fatty acid phytanic acid is degraded by the peroxisomal alpha-oxidation route because the 3-methyl group blocks beta-oxidation. In adult Refsum disease (ARD), peroxisomal alpha-oxidation is defective, which is caused by mutations in the gene coding for phytanoyl-CoA hydroxylase in the majority of ARD patients. As a consequence, phytanic acid accumulates in tissues and body fluids. This study focuses on an alternative route of phytanic acid degradation, omega-oxidation. The first step in omega-oxidation is hydroxylation at the omega-end of the fatty acid, catalyzed by a member of the cytochrome P450 multienzyme family. To study this first step, the formation of hydroxylated intermediates was studied in rat liver microsomes incubated with phytanic acid and NADPH. Two hydroxylated metabolites of phytanic acid were formed, omega- and (omega-1)-hydroxyphytanic acid (ratio of formation, 5:1). The formation of omega-hydroxyphytanic acid was NADPH dependent and inhibited by imidazole derivatives. These results indicate that phytanic acid undergoes omega-hydroxylation in rat liver microsomes and that an isoform of cytochrome P450 catalyzes the first step of phytanic acid omega-oxidation.

Refsum's disease (hereditary motor sensory neuropathy type IV, heredopathia atactica polyneuritiformis) is an autosomal recessive disorder the clinical features of which include retinitis pigmentosa, blindness, anosmia, deafness, sensory neuropathy, ataxia and accumulation of phytanic acid in plasma- and lipid-containing tissues. The transport and biochemical pathways of phytanic acid metabolism have recently been defined with the cloning of two key enzymes, phytanoyl-CoA 2-hydroxylase (PAHX) and 2-hydroxyphytanoyl-CoA lyase, together with the confirmation of their localization in peroxisomes. PAHX, an iron(II) and 2-oxoglutarate-dependent oxygenase is located on chromosome 10p13. Mutant forms of PAHX have been shown to be responsible for some, but not all, cases of Refsum's disease. Certain cases have been shown to be atypical mild variants of rhizomelic chondrodysplasia punctata type 1a. Other atypical cases with low-plasma phytanic acid may be caused by alpha-methylacyl-CoA racemase deficiency. A sterol-carrier protein-2 (SCP-2) knockout mouse model shares a similar clinical phenotype to Refsum's disease, but no mutations in SCP-2 have been described to-date in man. This review describes the clinical, biochemical and metabolic features of Refsum's disease and shows how the biochemistry of the alpha-oxidation pathway may be linked to the regulation of metabolic pathways controlled by isoprenoid lipids, involving calcineurin or the peroxisomal proliferator activating alpha-receptor.

Refsum's disease, or heredopathia atactica polyneuritiformis, is a peroxisomal disorder leading to the accumulation of phytanic acid throughout the body. It affects sensory and motor neurons and the skeletal system. Peripheral neuropathy, ataxia, blindness, deafness, and skeletal hyperostosis are significant findings used in the diagnosis of the disease.

Refsum's disease, firstly described almost 50 years ago by the Norvegian neurologist Sigvald Refsum, is an autosomic recessive disease affecting mostly the Scandinavians and the populations originating from Northern Europe. The disease results from a specific enzyme deficiency of the first step of phytanic acid catabolism pathway. This deficiency leads to an accumulation of this C20 fatty acid in the serum and the tissues with a preference for adipose tissue, liver and kidneys. The clinical picture includes retinitis pigmentosa, peripheral neuropathy, ataxia and elevated cerebrospinal fluid protein concentration. Other less frequent manifestations include cranial nerves deficiency, myocardiopathy, renal tubular dysfunction and ichtyosis. The diagnosis relies on serum phytanic acid measurement. The treatment consists of a phytanic-acid free diet sometimes associated with plasmapheresis. This treatment is generally effective on neuropathy but not on cranial nerves dysfunction and retinitis pigmentosa.

Peroxisome-deficient disorders including Zellweger syndrome (ZS), neonatal adrenoleukodystrophy (NALD) and infantile Refsum disease (IRD) are characterized by the absence of peroxisomes associated with secondary multiple enzyme deficiencies and by a defect in the neuronal migration. Collaborative complementation studies revealed the presence of at least 9 genetic groups among these disorders. Clinical phenotypes did not correlate with the genetic grouping. Responsible gene for one of these groups (group F) was determined as peroxisome assembly factor-1 (PAF-1) by the functional cloning using peroxisome-deficient CHO cell mutant. A patient of group F was a homozygote with C to T transitions in PAF-1 gene which resulted in a nonsense mutation. These results will pave the way for the elucidation of mechanisms of peroxisome biogenesis and the pathophysiology of neuronal migration.

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.

Several childhood multisystem disorders with prominent ophthalmological manifestations have been ascribed to the malfunction of the peroxisome, a subcellular organelle. The peroxisomal disorders have been divided into three groups: 1) those that result from defective biogenesis of the peroxisome (Zellweger syndrome, neonatal adrenoleukodystrophy, and infantile Refsum's disease); 2) those that result from multiple enzyme deficiencies (rhizomelic chondrodysplasia punctata); and 3) those that result from a single enzyme deficiency (X-linked adrenoleukodystrophy, primary hyperoxaluria type 1). Zellweger syndrome, the most lethal of the three peroxisomal biogenesis disorders, causes infantile hypotonia, seizures, and death within the first year. Ophthalmic manifestations include corneal opacification, cataract, glaucoma, pigmentary retinopathy and optic atrophy. Neonatal adrenoleukodystrophy and infantile Refsum's disease appear to be genetically distinct, but clinically, biochemically, and pathologically similar to Zellweger syndrome, although milder. Rhizomelic chondrodysplasia punctata, a peroxisomal disorder which results from at least two peroxisomal enzyme deficiencies, presents at birth with skeletal abnormalities and patients rarely survive past one year of age. The most prominent ocular manifestation consists of bilateral cataracts. X-linked (childhood) adrenoleukodystrophy, results from a deficiency of a single peroxisomal enzyme, presents in the latter part of the first decade with behavioral, cognitive and visual deterioration. The vision loss results from demyelination of the entire visual pathway, but the outer retina is spared. Primary hyperoxaluria type 1 manifests parafoveal subretinal pigment proliferation. Classical Refsum's disease may also be a peroxisomal disorder, but definitive evidence is lacking. Early identification of these disorders, which may depend on recognizing the ophthalmological findings, is critical for prenatal diagnosis, treatment, and genetic counselling.

This paper is on peroxisomes ("microbodies") dealing with various aspects of their physiological significance including the central question of biogenesis of peroxisomes. Attention is also focused on how peroxisomes are involved in human pathology and the so-called peroxisomal diseases are described.

A female patient started to develop deafness and vertigo at the age of 29. In the following years she became atactic and retinitis pigmentosa was discovered. The diagnosis of Refsum's disease was reached on the grounds of the high concentration of phytanic acid in plasma. The patient died 23 years after onset of the first symptoms. Liver, spleen and kidney showed lipofuscinosis and pigment-laden macrophages. The retina was atrophic and its pigment discontinuous. The meninges contained lipid-laden macrophages. The nerve cells in brain and spinal cord as well as the astrocytes and perivascular macrophages stored substances weakly PAS-positive and sudanophilic. The nerve cells accumulated lysosomes and residual bodies. In the astrocytes, the residual bodies were extremely polymorphous and contained inclusions with bilamellar ribbon-like structures. In the oligodendroglia the residual bodies displayed high electron density and finger print-like pattern. Peroxisomes were found in glial cells and microperoximes in neurons. The ultrastructural findings in the present case demonstrate that in terminal stages phytanic acid can reach the brain parenchyma passing through the BBB. Further autopsy studies will be necessary to determine whether these changes are consistent findings in Refsum's disease.

None of the single manifestations is in itself specific or pathognomonic for this disease except for the disturbance of the metabolism of phytanic acid. Therefore, clinical syndromes that involve similar manifestations without accumulations of phytanic acid should not be included under the term heredopathia atactica polyneuritiformis, or Refsum's disease. Whatever the biochemical mechanism that links phytanic acid accumulation with the clinical manifestations of heredopathia atactica polyneuritiformis, it appears that the observations made on patients following successful dietary treatment leave little doubt that most if not all of the manifestations in this disease are caused in some way by the accumulation of phytanic acid.

We examined liver biopsies from 4 patients with the infantile form of Refsum disease. No peroxisomes were visualized by light microscopy after cytochemical staining for catalase, a marker enzyme for this organelle. Absence of peroxisomes was confirmed by electron microscopy in 3 patients; in the 4th patient we observed organelles of peculiar size and structure and with minimal catalase activity. Light microscopy also showed birefringent macrophages containing P.A.S.-positive material; they were abundant in the 3 older children, and rare in the youngest (8 months). Peroxisomes and birefringent macrophages were absent in 2 patients with the cerebrohepatorenal syndrome of Zellweger. The simultaneous presence of these unique light microscopical characteristics may be of diagnostic value.

Peroxisomes are ubiquitous subcellular organelles varying in number, size and enzymatic content according to species, tissues or physiological states. Microperoxisomes are present in the central nervous system and in muscle. Peroxisomes participate in anabolic and catabolic processes, including ether-lipid synthesis, bêta-oxidation, bile acid synthesis, prostaglandin catabolism. Very long chain fatty acids are specific substrates of peroxisomal acyl-CoA oxidase. Peroxisomal disorders occur as two main groups: 1/ disorders with multiple deficiencies of peroxisomal functions: Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum disease, rhizomelic chondrodysplasia punctata; 2/ disorders with a single peroxisomal enzyme defect: X-linked adrenoleukodystrophy, acatalasemia, type 1 hyperoxaluria, pseudo-Zellweger syndrome. Present therapy is tentative with some limited success. It includes peroxisomal inductors and lipid-controlled diet. Prenatal diagnosis and heterozygote detection allow genetic counselling in some peroxisomal disorders.

Feeding of phytol in large doses (2-5% by weight in the diet) led to accumulation of phytanic acid in the mouse, rat, rabbit, and chinchilla, the degree of accumulation depending upon the level of dietary intake. The relative concentration of phytanic acid, expressed as a percentage of the total fatty acids, was as high as 20-60% in liver and 30-40% in serum. Phytenic acid, which may be an intermediate in the conversion of phytol to phytanic acid, also accumulated. When phytol was withdrawn from the diet, tissue and serum concentrations of phytanic acid fell rapidly, which indicates the ability of the normal animal to metabolize phytanic acid readily. At high dosages in the diet, phytol inhibited growth and caused death within 1-4 weeks. In the mouse, dietary phytanic acid and dietary phytol fed in equivalent amounts were of comparable toxicity. Accumulation of tissue phytanic acid occurred more rapidly when phytanic acid was fed than when phytol was fed in equal amounts. In none of the animals fed either phytol or phytanic acid were there any signs of neurological defects. Histologic examination of rats fed phytol showed some fat accumulation, glycogen depletion, and karyokinesis in the liver. There were no pathologic changes in the retina or in the peripheral and central nervous system such as those described in Refsum's disease.