Bile acids in amniotic fluid: promising metabolites for the prenatal diagnosis of peroxisomal disorders

Peroxisomes and bile acid biosynthesis

Peroxisomes play an important role in the biosynthesis of bile acids because a peroxisomal beta-oxidation step is required for the formation of the mature C24-bile acids from C27-bile acid intermediates. In addition, de novo synthesized bile acids are conjugated within the peroxisome. In this review, we describe the current state of knowledge about all aspects of peroxisomal function in bile acid biosynthesis in health and disease. The peroxisomal enzymes involved in the synthesis of bile acids have been identified, and the metabolic and pathologic consequences of a deficiency of one of these enzymes are discussed, including the potential role of nuclear receptors therein.

Biochemical analysis of cultured chorionic villi for the prenatal diagnosis of peroxisomal disorders: biochemical thresholds and molecular sensitivity for maternal cell contamination detection

OBJECTIVES

The prenatal diagnosis of peroxisomal disorders is most often performed by biochemical analysis of cultured chorionic villus sample (CVS) or amniocytes. We aimed to (a) highlight the risk of maternal cell contamination (MCC) in biochemical prenatal diagnosis, (b) establish the threshold of these biochemical assays to MCC, and (c) document the sensitivity of PCR based genotyping of microsatellites for the detection of MCC in prenatal diagnosis of inborn errors by biochemical analysis.

METHODS

The threshold of each biochemical assay was assessed by co-cultivating fibroblasts from known affected and normal individuals. Genotypes for three polymorphic loci were determined by PCR and GeneScan analysis. The sensitivity of the molecular test was determined by DNA mixing experiments and isolation of DNA from co-cultivated fibroblasts.

RESULTS

MCC was detected in 2.5% of at risk CVS cultures (n = 79). Co-cultivation of defective and normal fibroblasts demonstrated that the peroxisomal biochemical assays were accurate at 25% contamination. Very low level DNA or cell contamination (1-5%) was detectable by genotyping, but an allele did not yield a definitive peak based on morphology until approximately 10% contamination. Furthermore, we demonstrated that other inborn errors of metabolism might be more susceptible to diagnostic error by low level MCC.

CONCLUSION

The sensitivity of the microsatellite analysis (> or =10%) is well within the threshold of peroxisomal biochemical assays. Although peroxisomal biochemical assays would not be predicted to introduce a false positive or negative result if MCC <10% were present but not recognised by molecular analysis, the same may not be true for other inborn errors of metabolism.

Pre- and postnatal diagnosis of peroxisomal disorders using stable-isotope dilution gas chromatography--mass spectrometry

Quantitative analysis of the following peroxisomal metabolites is reported: very long-chain fatty acids (VLCFA), pipecolic acid, bile acid intermediates, phytanic and pristanic acid, in plasma, urine, cerebrospinal fluid (CSF), blood spots collected at neonatal screening and amniotic fluid. An overview is given of the concentrations of these metabolites in body fluids from control subjects and all patients investigated so far in this laboratory. The method of choice is gas chromatography -- mass spectrometry (GC-MS) with electron capture detection, combined with the use of stable-isotope-labelled internal standards.