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.

Central role of peroxisomes in isoprenoid biosynthesis

Peroxisomes contain enzymes catalyzing a number of indispensable metabolic functions mainly related to lipid metabolism. The importance of peroxisomes in man is stressed by the existence of genetic disorders in which the biogenesis of the organelle is defective, leading to complex developmental and metabolic phenotypes. The purpose of this review is to emphasize some of the recent findings related to the localization of cholesterol biosynthetic enzymes in peroxisomes and to discuss the impairment of cholesterol biosynthesis in peroxisomal deficiency diseases.

Peroxisomal disorders: clinical and biochemical studies in 15 children and prenatal diagnosis in 7 families

We describe the main clinical and biochemical findings in 15 patients with peroxisomal disorders, together with the results of 11 prenatal investigations for Zellweger syndrome. The initial laboratory diagnosis depended in most cases on demonstration of elevated very long chain fatty acids in plasma, but follow-up studies using cultured fibroblasts were essential for complete classification. The patient group comprises nine cases of Zellweger syndrome, one of neonatal adrenoleucodystrophy, two of infantile Refsum disease, one of bifunctional protein deficiency, and two of rhizomelic chondrodysplasia punctata. The study illustrates the clinical and biochemical variability of this group of patients and the detailed studies that are required for classification.