Immunocytochemical detection of peroxisomal beta-oxidation enzymes in cryostat and paraffin sections of human post mortem liver

Phosphomevalonate kinase is a cytosolic protein in humans

In the past decade, a predominant peroxisomal localization has been reported for several enzymes functioning in the presqualene segment of the cholesterol/isoprenoid biosynthesis pathway. More recently, however, conflicting results have been reported raising doubts about the postulated role of peroxisomes in isoprenoid biosynthesis, at least in humans. In this study, we have determined the subcellular localization of human phosphomevalonate kinase using a variety of biochemical and microscopic techniques, including conventional subcellular fractionation studies, digitonin permeabilization studies, immunofluorescence, and immunoelectron microscopy. We found an exclusive cytosolic localization of both endogenously expressed human phosphomevalonate kinase (in human fibroblasts, human liver, and HEK293 cells) and overexpressed human phosphomevalonate kinase (in human fibroblasts, HEK293 cells, and CV1 cells). No indication of a peroxisomal localization was obtained. Our results do not support a central role of peroxisomes in isoprenoid biosynthesis.

Human mevalonate pyrophosphate decarboxylase is localized in the cytosol

In the past decade several reports have claimed that peroxisomes play a critical role in the isoprenoid/cholesterol biosynthetic pathway based on the finding of a predominant peroxisomal localization of several of the enzymes involved. Other reports, however, do not support the peroxisomal localization of these enzymes. In this study we have studied the subcellular localization of one of the enzymes, human mevalonate pyrophosphate decarboxylase, by conventional subcellular fractionation and digitonin permeabilization studies, immunofluorescence microscopy, and immunoelectron microscopy. We found a cytosolic localization for both endogenous human mevalonate pyrophosphate decarboxylase (in human fibroblasts, liver, CV1 and HEK293 cells) and overexpressed mevalonate pyrophosphate decarboxylase (in human fibroblasts, HEK293 and CV1 cells) but no indication for a peroxisomal localization. Our results do not support a central role of peroxisomes in the isoprenoid/cholesterol biosynthetic pathway.

Mevalonate kinase is a cytosolic enzyme in humans

In the past decade several reports have appeared which suggest that peroxisomes play a central role in isoprenoid/cholesterol biosynthesis. These suggestions were based primarily on the reported finding of several of the enzymes of the presqualene segment of the biosynthetic pathway in peroxisomes. More recently, however, conflicting results have been reported raising doubt about the postulated role of peroxisomes in isoprenoid biosynthesis, at least in humans. In this study we have studied the subcellular localisation of human mevalonate kinase (MK) using a variety of biochemical and microscopical techniques. These include conventional subcellular fractionation studies, digitonin permeabilisation studies, immunofluorescence microscopy and immunocytochemistry. We exclusively found a cytosolic localisation of both endogenous human MK (human fibroblasts, liver and HEK293 cells) and overexpressed human MK (human fibroblasts, HEK293 cells and CV1 cells). No indication of a peroxisomal localisation was obtained. Our results do not support a central role for peroxisomes in isoprenoid biosynthesis.

Isolated dihydroxyacetonephosphate-acyl-transferase deficiency in rhizomelic chondrodysplasia punctata: clinical presentation, metabolic and histological findings

Rhizomelic chondrodysplasia punctata (RCDP) is clinically characterized by symmetrical shortening of the proximal limbs, contractures of joints, a characteristic dysmorphic face, and cataracts. In the classical form an impairment of several peroxisomal functions and enzymes (plasmalogen synthesis, phytanic acid oxidation, 3-oxoacyl-CoA thiolase) has been repeatedly shown. Recently a variant involving only the peroxisomal dihydroxyacetonephosphate acyltransferase (DHAP-AT) has been described. We present a patient with isolated DHAP-AT deficiency and all clinical, radiological and pathological features of classical RCDP. For the first time, microscopy and immunocytochemistry of hepatocytes could be performed.

CONCLUSION

In contrast to studies on classical rhizomelic chondrodysplasia punctata which have shown enlarged peroxisomes in numbers varying from hepatocyte to hepatocyte, the peroxisomes in our patient seem to be normal in size, number and shape.

In situ heterogeneity of peroxisomal oxidase activities: an update

Oxidases are a widespread group of enzymes. They are present in numerous organisms and organs and in various tissues, cells, and subcellular compartments, such as mitochondria. An important source of oxidases, which is investigated and discussed in this study, are the (micro)peroxisomes. Oxidases share the ability to reduce molecular oxygen during oxidation of their substrate, yielding an oxidized product and hydrogen peroxide. Besides the hydrogen peroxide-catabolizing enzyme catalase, peroxisomes contain one or more hydrogen peroxide-generating oxidases, which participate in different metabolic pathways. During the last four decades, various methods have been developed and elaborated for the histochemical localization of the activities of these oxidases. These methods are based either on the reduction of soluble electron acceptors by oxidase activity or on the capture of hydrogen peroxide. Both methods yield a coloured and/or electron dense precipitate. The most reliable technique in peroxisomal oxidase histochemistry is the cerium salt capture method. This method is based on the direct capture of hydrogen peroxide by cerium ions to form a fine crystalline, insoluble, electron dense reaction product, cerium perhydroxide, which can be visualized for light microscopy with diaminobenzidine. With the use of this technique, it became clear that oxidase activities not only vary between different organisms, organs, and tissues, but that heterogeneity also exists between different cells and within cells, i.e. between individual peroxisomes. A literature review, and recent studies performed in our laboratory, show that peroxisomes are highly differentiated organelles with respect to the presence of active enzymes. This study gives an overview of the in situ distribution and heterogeneity of peroxisomal enzyme activities as detected by histochemical assays of the activities of catalase, and the peroxisomal oxidases D-amino acid oxidase, L-alpha-hydroxy acid oxidase, polyamine oxidase and uric acid oxidase.

Localization of peroxisomal 3-oxoacyl-CoA thiolase in particles of varied density in rat liver: implications for peroxisome biogenesis

In this paper we report on the subcellular localization of peroxisomal thiolase in rat liver using density-gradient centrifugation and immunoelectron microscopy. The results obtained show that peroxisomes display great biochemical heterogeneity and can not be regarded as one homogeneous population of particles. We conclude that rat liver contains at least three distinct populations of peroxisomes, which are present both in normal-fed rats as well in rats treated with a plasticizer, di-(2-ethylhexyl)phthalate, known to induce peroxisomes. The following types of peroxisomes could be discerned: (1) Low-density peroxisomal particles containing 69-kDa peroxisomal membrane protein (PMP), dihydroxyacetonephosphate acyltransferase (DHAPAT) and the precursor form of peroxisomal thiolase (44-kDa). (2) Intermediate-density peroxisomal particles containing 69-kDa peroxisomal membrane protein, dihydroxyacetonephosphate acyltransferase, both 41-kDa (mature) and 44-kDa (immature) peroxisomal thiolase, catalase and D-aminoacid oxidase. (3) High-density peroxisomes containing 69-kDa peroxisomal membrane protein, dihydroxyacetonephosphate acyltransferase, 41-kDa thiolase, catalase and D-aminoacid oxidase.

The importance of tissue fixation for light microscopic immunohistochemical localization of peroxisomal proteins: the superiority of Carnoy's fixative over Baker's formalin and Bouin's solution

We have compared the effects of fixation with three commonly used fixatives upon preservation of the antigenicity of six peroxisomal proteins in rat liver using both immunohistochemical staining and Western blotting of fixed tissue extracts. The immunoreactivity of all six peroxisomal proteins was well preserved and peroxisomes were clearly identified in material fixed in Carnoy's fixative. Moreover, the corresponding proteins stained well in Western blots prepared from extracts of Carnoy-fixed material. The intensity of the immunohistochemical staining was reduced at different rates for individual peroxisomal proteins after fixation in Baker's formalin, but peroxisomes were still well visualized with antibodies to catalase and some beta-oxidation enzymes. No evidence of immunohistochemical staining for any peroxisomal antigens was obtained after fixation in Bouin's fluid. For detection of the antibody binding sites in Carnoy's fixed material, the avidin-biotin-peroxidase complex (ABC) with aminoethyl carbazole as chromogen was found to be superior to the methods of peroxidase-antiperoxidase/diaminobenzidine and protein A-gold with silver intensification. Using Carnoy-fixative and the ABC-method, we demonstrate light microscopic immunohistochemical localization of peroxisomal antigens in several rat tissues as well as in human post-mortem liver.

Immunoblot analysis of peroxisomal proteins in liver and fibroblasts from patients

Identification of a patient as suffering from a peroxisomal disorder usually starts by the finding of elevated very long-chain fatty acids in plasma and/or serum. This is followed by more detailed studies in blood, fibroblasts and tissues, including immunoblot analysis. Indeed, immunoblot analysis has become a valuable tool in the correct diagnosis and assignment of individual patients, except for X-linked adrenoleukodystrophy (X-ALD). We describe a simple immunoblotting procedure applicable to liver and fibroblast homo-genates using antibodies raised against catalase and the three beta-oxidation enzyme proteins acyl-CoA oxidase I, bifunctional protein and peroxisomal thiolase. The same procedure can also be used for chorionic villus biopsy specimens and has now become the method of choice for the prenatal diagnosis of Zellweger syndrome (and other disorders of peroxisome biogenesis) and rhizomelic chondrodysplasia punctata.

Immunocytochemical localization of peroxisomal proteins in human liver and kidney

The sample preparation and immunocytochemical methods for investigating the presence and subcellular localization of peroxisomal proteins (catalase, the three beta-oxidation enzymes, alanine : glyoxylate aminotransferase and a peroxisomal membrane protein) in human liver biopsies are described. We present a protocol for immunolabelling on ultrathin and semithin sections from the same tissue block, with protein A-colloidal gold as a reporter system. For this purpose, the tissue is embedded in Unicryl, a hydrophilic acrylic resin that is cured by ultraviolet illumination at 2 degrees C. The limitations and possibilities of the methods are discussed together with methodological problems. Cryostat sections of prefixed material should be used for the visualization by light microscopy of cytoplasmic catalase. It is emphasized that immunolabelling for catalase in formalin-fixed archival liver samples and in liver autopsy tissue (in the latter also for the peroxisomal beta-oxidation enzymes) permits visualization of peroxisomes; this can be helpful in diagnosing an index case retrospectively.

Secondary alterations of human hepatocellular peroxisomes

The morphological and morphometric characteristics of peroxisomes in normal human liver and the peroxisomal alterations in the liver of patients with acquired or congenital non-peroxisomal diseases are reviewed. Secondary peroxisomal changes are observed in steatosis, hepatitis and cirrhosis induced by various agents (viruses, alcohol, drugs, etc.), in cholestasis, in hepatomas, in extra-hepatic cancer with or without liver metastasis, in extrahepatic inflammatory processes, in metabolic disorders affecting metabolism of carbohydrates, lipids and lipoproteins, glycoproteins, amino acids, bilirubin or copper, and in altered thyroid hormone levels. They are recognized as a proliferation of peroxisomes (increased in number and to a lesser extent in surface density and volume density) often accompanied by a minor reduction in size (at most to 68% of the mean diameter in control livers) but very rarely by an increase in mean peroxisomal diameter, and as proliferation-related changes in shape (tails, gastruloid cisternae, funnel-like constrictions, elongation, protrusions) in at least a few of the peroxisomes. These secondary alterations of the peroxisomes are clearly distinguishable from the primary changes in peroxisomes observed in the liver of patients with congenital peroxisomal disorders.

Morphometry of peroxisomes and immunolocalization of peroxisomal proteins in the liver of patients with generalised peroxisomal disorders

Hepatic peroxisomes were studied by morphometric and immunocytochemical techniques in control patients and in four Zellweger syndrome patients, two infantile Refsum's (IRD) patients, one neonatal adrenoleukodystrophy (NALD) patient, and three patients with peroxisomal disorders (PD) which do not fit any currently recognised classification, but have disorders involving a defect in peroxisomal biogenesis. Peroxisomes which were ultrastructurally abnormal and greatly reduced in size and/or number were found in two of the Zellweger syndrome patients, and the NALD and IRD patients. There was variation in their numerical density ranging from none at all in two of the Zellweger syndrome patients to normal numbers in the IRD patients. In most patients there was a decrease in the immunolabelling of catalase over the peroxisomes. In the Zellweger syndrome and NALD patients, the small, abnormal peroxisomes did not label for any of the beta-oxidation proteins. The IRD patients and the PD patients however, were heterogeneous with respect to beta-oxidation labelling. The ultrastructural heterogeneity of peroxisomes in these peroxisomal disorders patients indicates there may be genotypic differences between the major groups and also within each group. The common factor in all the patients in this study where peroxisomes were present was the presence in the hepatic peroxisomes of an electron dense centre which did not label immunocytochemically for catalase or the beta-oxidation enzymes. This electron dense centre may indicate a structural abnormality in the peroxisomes in these patients.

Cytoplasmic catalase and ghostlike peroxisomes in the liver from a child with atypical chondrodysplasia punctata

In the liver biopsy from an 8.5-year-old girl with the biochemical characteristics of rhizomelic chondrodysplasia punctata (RCDP), but with normal limbs, normal catalase-containing peroxisomes were absent. Light microscopy after diaminobenzidine staining for catalase activity (the peroxisomal marker enzyme) and immunostaining against catalase protein indicated a cytosolic localization of the enzyme. By electron microscopy, rare and extremely large, irregularly shaped vesicles were found in the parenchymal cells. The three peroxisomal beta-oxidation enzymes (acyl-CoA oxidase, bi(tri)functional enzyme, and 3-ketoacyl-CoA thiolase) and alanine-glyoxylate aminotransferase were immunolocalized in these organelles. However, a weak to negative label was obtained after staining against catalase. Diaminobenzidine staining demonstrated a minimal catalase reaction product in some vesicles only. Morphometry revealed a corrected mean d-circle of 1.44 microns and a maximum d-circle of 2.767 microns (controls: 0.635 microns and 1.027 microns, respectively). Numerical, volume, and surface densities were reduced to 3%, 41%, and 17% of control values, respectively. The large size, irregular shape, and rarity of the organelles are morphologic features of peroxisomal "ghosts." It seems that in this patient, apart from the known peroxisomal defects in RCDP, catalase incorporation into the peroxisomes is impaired together with a normal proliferation (division) of the organelles. In the cultured skin fibroblasts from the patient, however, immuno-electron microscopy showed normal catalase-containing peroxisomes in apparently normal numbers.

Peroxisomal disorders in children: immunohistochemistry and neuropathology

Immunohistochemical studies with antisera against four peroxisomal enzymes, catalase and beta-oxidation enzymes (acyl-coenzyme A oxidase, bifunctional protein, and 3-ketoacyl-CoA thiolase), were performed on brain, liver, and kidney specimens from patients with peroxisomal disorders, as well as specimens from three control subjects, by using conventional paraffin-embedded autopsy material. The patients included eight with Zellweger syndrome and one with neonatal adrenoleukodystrophy. In the liver and kidney specimens from all patients, except one with Zellweger syndrome, diffuse immunostaining with all antisera in the cytoplasm of hepatocytes and renal tubular epithelium suggested an absence of peroxisomes but the presence of peroxisomal enzymes. Examination of brain specimens indicated a weak or negative reaction of neurons in the cerebral cortex and a weak reaction of glial cells in the white matter, which suggested maturational delay compared with control subjects. The delayed immunoreactive pattern of peroxisomal enzymes in Zellweger syndrome and neonatal adrenoleukodystrophy may be related to the significant neuropathologic features of polymicrogyria and dysmyelinogenesis. One patient with Zellweger syndrome had a unique finding of a positive granular catalase reaction and a negative reaction with antisera to 3-ketoacyl-coenzyme A thiolase, which suggested a diagnosis of pseudo-Zellweger syndrome. This study validates the application of these immunohistochemical methods to the study of peroxisomal enzymes. Use of these methods improves the accuracy of diagnosis of peroxisomal disorders.

Human liver pathology in peroxisomal diseases: a review including novel data

Results from electron microscopic morphometry, enzyme cytochemistry and immunolocalization in liver biopsies are reviewed. Emphasis is put on the following aspects: 1) relationship between peroxisomal size and enzyme concentration; 2) abnormal enlargement of peroxisomes in many congenital disorders with peroxisomal dysfunction; 3) normal localization of matrix enzymes in several patients with peroxisomal dysfunction, with the exception of catalase, which is mainly cytoplasmic; 4) ghost-like peroxisomes in the liver of several syndromes but not in nine cases labelled as Zellweger; 5) discrepancies between liver and cultured fibroblasts; 6) trilamellar, regularly spaced inclusions, large stacks of which are birefringent, indicate a peroxisomal dysfunction; their absence does not exclude it. The same rule holds for lipid in macrophages which is insoluble in acetone and n-hexane (after fixation). The chemical nature of these two storage materials remains unclear; and 7) proliferation of human peroxisomes is frequent in acquired liver diseases and drug toxicity, but is never accompanied by an increase in size, in contrast to the effect of the fibrates and phthalates in rat and mouse. Novel data from seven peroxisomal patients are included.

Neonatal seizures and severe hypotonia in a male infant suffering from a defect in peroxisomal beta-oxidation

In this paper, we describe a baby male born to healthy non-consanguineous parents presenting at birth with hypotonia and seizures. Additional salient clinical features included the development of glaucoma, the absence of significant facial dysmorphism and the absence of liver enlargement or renal cysts. The patient died at the age of 3 months. At autopsy, liver fibrosis and kidney glomerulosclerosis were noted. Neuropathological findings included pachygyria of the olivary nuclei and cerebellar neuronal heterotopias. There was no evidence for a demyelinating process. Biochemically, the patient was found to have elevated plasma levels of very-long-chain fatty acids (VLCFA) and abnormal bile acid intermediates, whereas other indicators of peroxisomal function (plasmalogen biosynthesis and plasma pipecolic acid) were normal. Catalase staining of a liver biopsy specimen revealed peroxisomes to be present in normal numbers, although some were abnormally large. Trilamellar inclusions typical of a peroxisomal fatty acid oxidation defect were present in macrophages. Indeed, beta-oxidation of the very-long-chain fatty acid hexacosanoic acid (C26:0) was found to be strongly deficient. Fatty acyl-CoA oxidase activity in the patient's liver was normal, however. Furthermore immunocytochemical studies using antibodies against acyl-CoA oxidase, bifunctional protein and peroxisomal thiolase, revealed the normal localization of all three enzyme proteins within the peroxisomes. We suggest that our patient has a selective peroxisomal beta-oxidation defect, a recently identified heterogeneous group of early-onset peroxisomal disorders distinct from the Zellweger syndrome and other generalized peroxisomal disorders.

Different types of peroxisomes in human duodenal epithelium

Peroxisomes are ubiquitous organelles containing enzyme sequences for beta oxidation of fatty acids, synthesis of bile acids, and ether phospholipids. In the inherited peroxisomal diseases one or more enzymes are deficient in hepatic, renal, and fibroblast peroxisomes. We have examined peroxisomes by light and electron microscopy in 29 duodenal biopsy specimens (21 with normal mucosa) after staining for catalase activity, a marker enzyme. Peroxisomes were most numerous in the apices of the nucleus and at the villus base. Two types were distinguished: rounded to oval forms with a median lesser diameter of 0.23-0.31 microns, and tubular, vermiform organelles 0.1 microns thick and up to 3 microns long. Both types coexist in most patients. Tilting of sections and examination of semithin sections at 120 kV did not show connections between individual organelles. By morphometry, volume density was at least 0.45-0.62% of cellular volume, compared to 1.05% in human liver. In contrast, in four out of five individuals surface density of the peroxisomal membrane was 1.4-2.3 times higher than in control livers; this is expected to favour the exchange of metabolites. We suggest that intestinal peroxisomes contribute substantially to the breakdown of very long chain fatty acids.

Peroxisomal localization of the immunoreactive beta-oxidation enzymes in a neonate with a beta-oxidation defect. Pathological observations in liver, adrenal cortex and kidney

A boy born to healthy, unrelated parents, presented at birth with hypotonia and seizures. Very long chain fatty acids in the plasma were strongly elevated; bile acid intermediates and plasmalogen biosynthesis were normal. Acyl-CoA oxidase activity was normal. The patient died at the age of 3 months. The cerebellum and medulla oblongata showed neuronal migration defects. The specific biochemical basis for the impaired peroxisomal beta-oxidation has not been found. The three immunoreactive peroxisomal beta-oxidation enzymes and catalase were localized in the hepatocellular peroxisomes. Aberrant features of the peroxisomes included: a subpopulation of organelles larger than 1 micron, an amorphous nucleoid in many organelles, and invaginations of the peroxisomal membrane into the matrix. Peroxisomes in the proximal renal tubules also contained the three immunoreactive beta-oxidation enzymes. Regularly spaced trilamellar inclusions were seen in hepatic macrophages; they were much more abundant in adrenocortical macrophages. The inclusions were birefringent and resistant to acetone extraction. Distinct hepatic fibrosis had developed over a period of 2.5 months. We speculate that the impaired beta-oxidation is due to a defect at the level of the peroxisomal carnitine octanoyl or -acetyl transferase, responsible for the export of beta-oxidation products.

The role of histochemical investigations in metabolic disorders affecting the liver

The application of histochemical techniques to the study of metabolic disorders affecting the liver can yield considerable information, provided the methods used are sound and the interpretation is not over-enthusiastic. The appropriate methods can give insight into liver function and can identify and localize a wide variety of carbohydrates, lipids, proteins and enzyme activities. It is often thought that tissue taken for histochemical analysis cannot be used for morphology, but properly prepared tissue will provide the architectural and cytological detail necessary for histological assessment. There are several advantages to the histochemical approach, the main ones being economy of use of the valuable tissue sample (in theory about 100 sections and tests can be done on a 1 mm depth of tissue) and that the results of the tests can be assessed in relation to the structure of the liver. There are two areas in which histochemical investigations are used: firstly, to detect cellular constituents, structures and cells not otherwise visible by routine methods. In this mode, histochemistry is an extension of the histological approach and constitutes a 'super haematoxylin and eosin' stain. Secondly, it is possible to assess enzyme activities and their localization, and in some well-defined instances to offer reliable indications of whether there is deficient activity, normal activity or enhanced activity. Although there is a body of opinion which believes that quantitative enzyme histochemistry is possible and reliable, the author has not found the data, in particular or lysosomal enzymes, to be reliable and remains unconvinced that this technique has a place in the study of pathological tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Liver pathology and immunocytochemistry in congenital peroxisomal diseases: a review

Diagnostic and pathogenetic investigations of peroxisomal disorders should include the study of the macroscopic and microscopic pathology of the liver, in addition to careful clinical observations, skeletal X-ray and brain CT scan, assays of very long-chain fatty acids and bile acid intermediates, and selected enzyme activities. This review of the literature also contains novel observations about the following syndromes: cerebro-hepato-renal (Zellweger) syndrome, X-linked and neonatal adrenoleukodystrophies (ALD, NALD), NALD-like syndromes, infantile phytanic acid storage, classical Refsum disease, rhizomelic and other forms of chondrodysplasia punctata (XD, XR, AR), hyperpipecolic acidaemia, primary hyperoxaluria I, pseudo-Zellweger and Zellweger-like syndromes, and single enzyme deficiencies. Microscopic data include catalase staining and morphometry of peroxisomes, immunolocalization of beta-oxidation enzymes, detection of trilamellar, polarizing inclusions in PAS-positive macrophages, fibrosis and iron storage. Peroxisomal enlargement appears to be related to functional deficit in beta-oxidation disorders as well as in rhizomelic chondrodysplasia punctata. Because normal peroxisomal localization of active beta-oxidation enzymes can accompany a C26 beta-oxidation deficit, other mechanisms such as impaired transport of metabolites should be investigated. 'Ghost'-like organelles are shown in the liver of an infantile Refsum patient and in an NALD-like case; immuno-gold labelling of membrane proteins did not reveal ghosts in Zellweger livers.

Immunocytochemical localization of peroxisomal beta-oxidation enzymes in human fetal liver

In the majority of congenital peroxisomal disorders, beta-oxidation of very long chain fatty acids is deficient. We have investigated the appearance and localization of the three peroxisomal beta-oxidation enzymes in normal fetal liver (fertilization age between 5 and 18 weeks) with protein A-gold immunocytochemistry and silver enhancement for light microscopic visualization. With specificity-tested polyclonal antibodies, acyl-CoA-oxidase, bifunctional enzyme, and 3-oxoacyl-CoA thiolase were localized in the peroxisomes of the parenchymal cells, which appear as brown or black granules. In the youngest specimen, no immunopositive reaction was obtained. A weak reaction with anti-thiolase was obtained at the age of 6-7 weeks. At a fertilization age of 8 weeks, peroxisomes could be distinctly visualized after immunostaining for all three enzymes. From a staining series with anti-thiolase on simultaneously treated slides, it appears that the amount of antigen per peroxisome and the organelle size increase between the seventh and eighteenth weeks. These data should enable a more specific diagnosis in fetal liver biopsies from pregnancies at risk and after termination of pregnancy.