Heterogeneity in di/trihydroxycholestanoic acidaemia

Liver disease caused by failure to racemize trihydroxycholestanoic acid: gene mutation and effect of bile acid therapy

BACKGROUND & AIMS

Inborn errors of bile acid metabolism may present as neonatal cholestasis and fat-soluble vitamin malabsorption or as late onset chronic liver disease. Our aim was to fully characterize a defect in bile acid synthesis in a 2-week-old African-American girl presenting with coagulopathy, vitamin D and E deficiencies, and mild cholestasis and in her sibling, whose liver had been used for orthotopic liver transplantation (OLT).

METHODS

Bile acids were measured by mass spectrometry in urine, bile, serum, and feces of the patient and in urine from the unrelated recipient.

RESULTS

Liver biopsy specimens showed neonatal hepatitis with giant cell transformation and hepatocyte necrosis; peroxisomes were reduced in number. High concentrations of (25R)3alpha,7alpha,12alpha-trihydroxy-5beta-cholestanoic acid in the urine, bile, and serum established a pattern similar to that of Zellweger syndrome and identical to the Alligator mississippiensis. Serum phytanic acid was normal, whereas pristanic acid was markedly elevated. Biochemical, MRI, and neurologic findings were inconsistent with a generalized defect of peroxisomal function and were unique. Analysis of the urine from the recipient of the deceased sibling's liver confirmed the same bile acid synthetic defect. A deficiency in 2-methylacyl-CoA racemase, which is essential for conversion of (25R)THCA to its 25S-isomer, the substrate to initiate peroxisomal beta-oxidation to primary bile acids, was confirmed by DNA analysis revealing a missense mutation (S52P) in the gene encoding this enzyme. Long-term treatment with cholic acid normalized liver enzymes and prevented progression of symptoms.

CONCLUSIONS

This genetic defect further highlights bile acid synthetic defects as a cause of neonatal cholestasis.

Clinical approach to inherited peroxisomal disorders: a series of 27 patients

To illustrate the clinical and biochemical heterogeneity of peroxisomal disorders, we report our experience with 27 patients seen personally between 1982 and 1997. Twenty patients presented with a phenotype corresponding either to Zellweger syndrome, neonatal adrenoleukodystrophy, or infantile Refsum disease, 3 of whom had a peroxisomal disorder due to a single enzyme defect. One patient had a mild form of rhizomelic chondrodysplasia punctata, 1 had classic Refsum disease. Finally, 5 patients presented with clinical manifestations that were either unusually mild or completely atypical, and initially did not arouse suspicion of a peroxisomal disorder. They showed multiple defects of peroxisomal functions with one or several functions remaining intact, suggesting a peroxisome biogenesis disorder. The defect in peroxisome biogenesis was further characterized by variable expression in different tissues and/or individual cells in 5 patients. Studies restricted to fibroblasts failed to identify abnormalities in this group. We demonstrate that clinical manifestations of peroxisomal disorders may be very mild or completely atypical, and therefore, peroxisomal disorders should be considered in a variety of clinical settings. Furthermore, we suggest performing extensive peroxisomal investigations in every patient suspected of suffering from a peroxisomal disorder, even when the clinical presentation is typical.

Ataxia associated with increased plasma concentrations of pristanic acid, phytanic acid and C27 bile acids but normal fibroblast branched-chain fatty acid oxidation

Investigations of peroxisomal function were undertaken in an 8-year-old girl who developed motor difficulties at the age of 3.5 years and went on to develop a progressive ataxia and dysarthria. There were no other neurological abnormalities and she was of normal intelligence. Analysis of plasma very long-chain fatty acids revealed a normal C26 concentration and normal C24/C22 and C26/C22 ratios. Analysis of branched-chain fatty acids showed an elevated plasma phytanic acid concentration of 60 mumol/L (normal < 15) and a considerably elevated pristanic acid concentration of 50 mumol/L (normal < 2). Plasma concentrations of the C27 bile acids 3 alpha, 7 alpha-dihydroxycholestanoic acid (DHCA) and 3 alpha, 7 alpha, 12 alpha-trihydroxycholestanoic acid (THCA) and of the C29-dicarboxylic acid were also increased. We postulated that these results might be due to deficiency of the peroxisomal branched-chain acyl-CoA oxidase, but when oxidation of branched-chain fatty acids was studied in cultured skin fibroblasts it was found to be normal. Alternative explanations for the accumulation of branched-chain substrates for peroxisomal beta-oxidation are discussed. Treatment with a low-phytanic acid diet arrested the progression of the ataxia and led to a slight improvement.

Peroxisomal disorders: a review

Until recently peroxisomal disorders were considered to be extremely rare and the diagnostic procedures available for postanatal and prenatal diagnosis were not widely known. At present, 17 human disorders are linked to peroxisomal dysfunction. The clinical, biochemical and morphological peroxisome heterogeneity described in the different diseases illustrate that only combined analysis of all the different approaches will lead to a correct diagnosis and a coherent pathophysiological model to guide ongoing research. With the study of human peroxisomal disease, advances have been gained as to the function of the peroxisome in normal and pathological conditions. Genetic analysis of peroxisome biogenesis and research on peroxisomal targeting signals are now in progress. Peroxisomal disorders are usually classified according to the degree of biochemical impairment. In this paper, a tentative classification of peroxisomal disorders will be proposed, based on the degree of biochemical abnormalities combined with new data obtained on whether or not defective peroxisome assembly is involved: (1) disorders with peroxisome assembly deficiencies; (2) disorders with single enzyme deficiencies. The clinical onset and the major symptoms of the various disorders, and the recently discovered findings are discussed.