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Objective: Peroxisomal blood tests are generally considered to be conclusive. We observed several patients with a clinical and MRI phenotype suggestive of an infantile onset peroxisomal defect, but no convincing abnormalities in initial peroxisomal blood tests. Brain MRI showed typical abnormalities as observed in the neonatal adrenoleukodystrophy variant of infantile peroxisomal disorders. Our aim was to evaluate the accuracy of this MRI diagnosis with further peroxisomal testing., Methods: We searched our database of unclassified leukoencephalopathies and found 6 such patients. We collected clinical data and scored available MRIs of these patients. We performed further peroxisomal studies in fibroblasts, including immunofluorescence microscopy analysis with antibodies against catalase, a peroxisomal matrix enzyme. We performed complementation analysis and analyzed the suspected genes., Results: We confirmed the diagnosis of Zellweger spectrum disorder in 3 patients and D-bifunctional protein deficiency in the others. The clinical findings were within the spectrum known for these diagnoses. Sequential MRIs showed that the abnormalities started in the hilus of the dentate nucleus and superior cerebellar peduncles. Subsequently, the cerebellar white matter and brainstem tracts were affected, followed by the parieto-occipital white matter, splenium of the corpus callosum, and posterior limb of the internal capsule. Eventually, all cerebral white matter became abnormal. The thalamus was typically affected as well., Conclusions: If MRI reveals abnormalities suggestive of infantile onset peroxisomal defects, negative peroxisomal blood tests do not exclude the diagnosis. Further tests in fibroblasts should be performed, most importantly immunofluorescence microscopy analysis with antibodies against catalase to stain peroxisomes.

The biochemical hallmark of adult Refsum disease (ARD) is an isolated deficiency in the breakdown of phytanic acid. This usually results from a PHYH gene defect, although some cases have been found to carry a PEX7 defect. We describe the phenotype of such a patient, indistinguishable from that of classic ARD. Hence, we propose the subdivision of ARD into type 1 and type 2, depending on which gene is defective.

This article describes two siblings with infantile Refsum disease (IRD) whose initial presentation was that of malabsorption and mimicked a-beta- or homozygous hypo-beta-lipoproteinemia. Failure to recognize IRD in the first-born child precluded proper genetic counseling and prenatal diagnosis in subsequent pregnancies and also caused considerable delay in diagnosing IRD in the second child. The clinical heterogeneity of peroxisomal disorders constitutes a diagnostic challenge, which demands a high degree of awareness from the part of the clinician. This is particularly the case with IRD, where protracted diarrhea with low serum cholesterol levels appears to be a frequently occurring initial feature during the 1st months of life.

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.